The Universe (2007–…): Season 3, Episode 3 - Light Speed - full transcript
Physical behavior that results from having a constant speed of light are described.
In the beginning, there was darkness...
and then... BANG!...
giving birth to an endless
expanding existence...
of time, space, and matter.
Now, see further than
we've ever imagined...
beyond the limits of our existence...
in a place we call "The Universe."
Streaking through space...
light is the fastest
thing in the universe.
It could circle the Earth
seven times in one second.
As it reaches us
across vast distances...
it reveals the history of the cosmos.
We're able to look back in time.
Light travels at
186,000 miles per second.
Its speed is an ultimate barrier.
Nothing can go faster.
We have never ever
broken the speed limit.
But is the answer final?
Will spaceships ever
speed faster than light?
Is it even worth trying?
To give up without
trying is just giving up.
It can neither be touched nor felt.
It is an abstract quantity
of immense impact...
the rate of motion at the very
heart of all existence.
The fundamental lynchpin
of the universe...
that we call light speed.
On planet Earth, where
speed is in demand...
the fastest people,
vehicles, and technologies...
seem to crawl in a cosmos
where light speed is king.
More than king, the speed of
light is the cornerstone...
on which the universe is built.
There's a famous saying in physics...
which is that the speed of light is
not just a good idea, it's the law.
The speed of light is one of
the most important speed limits...
in the entire universe.
The speed of light,
186,000 miles per second...
is just incredible.
I mean, if light traveled in
a circle around the Earth...
it could circle the Earth
seven times in one second.
That's an incredible speed.
That incredible speed is
the first thing we encounter...
when confronting
the phenomenon of light.
To say it is fast is
a colossal understatement.
It's amazing to me that when
I talk on my cell phone...
I can talk to somebody
clear across the country...
and I'm not really
aware of any time lag...
and that signal is going
from my phone to a tower...
up to a satellite, back down,
and it seems instantaneous.
So we really take for granted...
the speed of light could
practically be infinite to us.
Physics professor
Clifford Johnson of USC...
is an avid bike rider.
Circling a track, he
considers trying to cover...
the same 186,000 miles that
light does in one second.
He'll find, however, that his
work will be cut out for him.
To travel the distance that
light moves in just one second...
it would take me 22 months on a bike...
moving at 12 miles an hour,
cycling 24 hours a day.
But the speed of light,
in relation to the speed of life...
makes our world work in just
the way we've come to expect.
One of the beneficial
effects for humanity...
of having the speed of
light be as fast as it is...
is that what you see is what you get.
Light speed makes everyday
experience virtually instantaneous.
When the light bulb goes
on, you see it right away.
Anything that happens around
you registers immediately.
And certain experiences
make it crystal clear...
that light travels faster than
anything else, including sound.
One interesting consequence
of the great speed...
with which light travels is that
you see a flash of lightning...
essentially instantaneously...
but you hear the thunder only later on.
But light speed has its limits...
when stacked up to a place
as large as the universe.
We think that the speed of light...
is unimaginably fast on a human scale.
However, in astronomical terms,
it's actually kind of pokey.
And so it's ironic that when
the Apollo spacecraft blasted into space...
traveling at what seemed
an amazing 25,000 miles per hour...
the speed of light proved
frustratingly slow...
when it came time to
talk to astronauts...
236,000 miles away on the lunar surface.
So when the astronauts
were on the Moon...
and people asked Neil Armstrong...
"Hey, Neil, what's it like up there?"
Several seconds went by
between the question...
and Neil Armstrong's answer.
Neil, this is Houston.
Radio check, over.
Aye, roger, Houston, loud and clear.
- Roger out.
- Loud and clear, Houston.
Roger, Buzz.
And those several seconds...
were not because he was
thinking about the answer...
but rather because
it took 1.3 seconds...
for the signal traveling
at the speed of light...
to reach Neil from Mission Control...
and another 1.3 seconds for his reply...
using radio waves to come back...
and that's 2.6 seconds
without even thinking.
Okay.
The 1.3 seconds it takes light to
travel from the Earth to the Moon...
is pocket change compared
to other celestial bodies.
Light from the Sun, for instance...
takes more than eight
minutes to get to the Earth.
If the Sun were to
disappear right now...
if the Sun were to suddenly vanish...
it would take eight minutes...
before we would even
feel the shockwave...
and see the effects
of a disappearing sun.
The limits of light speed...
also make communicating with
Earth's far-flung spacecraft...
a special challenge.
It takes up to 44 minutes for
signals to travel back and forth...
to the probes exploring Mars...
more than three hours
to Cassini at Saturn...
and over 29 hours to Voyager 1,
the most distant of all...
now heading out of the solar system.
Still, these distances are
trivial on a cosmic scale.
We can almost understand
the 10 billion miles...
separating Earth from Voyager...
but what's next?
The nearest star is a red
dwarf named Proxima Centauri...
nearly 25 trillion miles away.
That's 25 followed by 12 zeroes.
I am often asked a question,
"How can you, as an astronomer...
"really comprehend these vast
distances, " these huge numbers?"
And the answer is, I can't.
The human brain really doesn't
wrap itself around numbers that big.
Occasionally, I actually write out...
how many zeroes there are in
kilometers from here to a galaxy...
just to see how huge that number is.
But in reality, of course,
as astronomers...
we would be spending
all day writing zeroes...
unless we came up with
a better unit to use...
and that's what a light-year is.
A light-year is approximately
6 trillion miles.
It's the distance that
light travels in one year.
Using light-years to
describe distances...
opens up another dimension
of light speed's character.
Think of it. Sirius,
the brightest star in the sky...
is 8.6 light-years away.
That means we see it,
not as it is today...
but as it was 8.6 years ago.
We see the bright star Vega
as it was 25 years ago...
and the red super giant
Betelgeuse as it was 500 years ago.
It's a wonderful gift of nature...
that because it takes time to travel,
we're able to look back in time.
The further out we look in distance,
the further back in time we look.
We would have no idea what
our cosmic history was...
if the speed of light
traveled instantaneously.
Laura Danly is curator of the historic
Griffith Observatory in Los Angeles.
With light's ability to
take us into the past...
she's assembled a stack of photos...
that tell light speed's story
of the universe in snapshots...
looking back in time to its beginning...
more than 13 billion years
ago to the present day.
I'm putting together a scrapbook...
of the history of our
family of galaxies...
and I chose all the galaxies that
we can see with our telescopes...
as far back as we can
see with our telescopes.
Each photo in this album, then,
shows something in the universe...
with a look-back time equivalent
to its distance in light-years.
The famous Crab Nebula,
6,500 years ago...
the Galactic Core,
center of the Milky Way...
26,000 years ago...
and the Andromeda galaxy,
our next-door neighbor...
2.5 million years ago...
but practically yesterday
on a cosmic scale.
I love this cluster.
For almost 90 percent
of the look-back time...
the album is filled
with common galaxies.
Common, yes, but intriguingly diverse.
And these two are colliding.
You can see one going...
what appears to be right
through the other...
and there's a lot of drama
in the way galaxies evolve...
and the way they
interact with one another.
So this one would be...
Oh, well, it's only about
500 million light-years away.
As Danly places each
shot in the album...
a bigger picture begins to emerge.
Adult galaxies have been
the main characters...
evolving in all their variety
for the past 12 billion years.
But the cosmos also has
its childhood photos...
showing galaxies when
the universe was a mere toddler.
These are actually very
interesting galaxies...
at about 11 billion light-years away.
These compact galaxies are-
Represent what might be
a 2 or 2 1/2-year-old child...
you know, just really
learning how to walk.
But even these galaxies have
their younger brothers and sisters.
This spectacular shot
shows a gravity lens...
a cluster of galaxies 2.2
billion light-years away...
that bends light, allowing us to
see much further in space and time.
The lens reveals a tiny speck...
identified as one of the earliest
galaxies we can see...
as it was 13 billion light-years ago...
still an infant in
the evolving universe.
Galaxies, when they were babies...
really don't have a lot of
distinguishable features.
They're kind of blobs.
They don't really have
a lot of structure.
The universe, as a whole,
was something of a blob...
at the beginning of its life, too.
What we see of that time are
the first light waves in history...
reaching us only now...
13.7 billion years after
they flashed into existence.
We see them in the picture of
an afterglow from the Big Bang...
and they are known today...
as the cosmic microwave
background radiation.
The cosmic microwave
background radiation...
is the most distant thing we can see.
It is, in a sense, the picture
of the baby upon delivery.
NASA's All-Sky Picture
reveals a glow...
that is uniform everywhere we can see...
the universe as it was in
a cosmic moment after its birth.
But here, our view
comes to a sudden halt.
What we can see of
the universe is limited...
not by the size or power
of our instruments...
but by the barrier
of light speed itself.
How can the fastest
thing in the universe...
make us blind to the infinity of space?
Knowing that light speed is
6 trillion miles per year...
gives us the light-year,
a convenient shorthand...
for talking about the huge
distances in the universe.
But it's just as
important to understand...
that light speed at 6
trillion miles per year...
is an ironclad constant.
The speed of light is so constant...
that the universe actually
changes everything...
so that you never see
it going any other speed.
So the speed of light really is
the measuring stick of the entire universe.
In fact, the constancy of light speed...
results in an amazing tool
for measuring distance...
in the vastness of space.
The tool is called red shift.
It happens as light between
galaxies travels at a fixed speed.
When the space between
the galaxies expands...
the light racing between
them gets stretched...
turning red in color.
As light goes from one
galaxy to another...
from a distant galaxy to
our own, for example...
that light gets stretched along
with the stretching of space...
and that causes intrinsically
short-wavelength light...
like blue light...
to gradually become
long-wavelength or redder light.
That fundamentally is the cause
of the red shift that we see...
in the spectra of galaxies.
How does the red shift turn
into a way to measure distance?
It's all because of an astonishing
discovery made in 1926...
at the Mount Wilson
Observatory outside Los Angeles.
Being up here on Mount Wilson
is always a thrill for me...
because it was actually
right here at this location...
that our view of
the universe entirely changed.
It was here that Edwin Hubble found
out the universe is expanding...
and that was an amazing thing.
He wasn't expecting it.
Nobody thought that was the case,
and it changed everything.
Seeing red shifts everywhere...
Hubble found that all of
the universe's galaxies...
were moving away from each other...
which we now know is caused by
the expansion of space itself.
As seen from the Earth...
a galaxy doesn't look
like it's moving away...
but we know that it is because
its light is red-shifted.
A galaxy moving away at low
speed has a slight red shift.
A galaxy moving faster
has a larger red shift.
But Hubble found that those
faster-moving galaxies...
are also farther away.
That meant the greater the red shift...
the more distant the galaxy.
By seeing how fast space is expanding...
and working the math backwards...
cosmologists have been able to
estimate the age of the universe.
Combine that with light speed...
and you have a major brain twister.
The universe is such a huge place...
that the light travel time
really becomes important to us.
We believe the universe began
about 13 1/2 billion years ago.
That means the farthest in
any direction we can look...
is 13 1/2 billion light-years.
There hasn't been enough time for
light to travel more than that.
It's called our light horizon...
a sphere 13 1/2 billion
light-years in all directions...
containing everything we can see.
But that's where the brain
twister comes in.
Does space end there?
We have no reason to believe
that the distance we can see...
is the entire size of the universe.
In fact, it might be
much bigger than that.
It's just that, with
light travel time...
that's all we can see.
That's our horizon.
So, consider this conundrum.
Astronomers in a galaxy at
one edge of our horizon...
can't possibly see any galaxies
on the other edge of our horizon...
but they can see galaxies...
13 1/2 billion light-years
in the other direction...
and so can astronomers at
the edge of their horizon...
and on and on, perhaps to infinity.
As for astronomers on Earth,
light speed has them trapped.
If we ask what is happening
beyond our light horizon...
we have to face the fact...
that the speed of light
really is a barrier.
We've never seen anything
beyond our light horizon.
Can we take comfort in the fact...
that there is so much to
see inside our horizon?
This breathtaking shot is the Hubble
Space Telescope's Ultra Deep Field.
It's a massively detailed
photo of an area of the sky...
a hundred times smaller
than the full Moon...
yet containing 10,000 galaxies...
some whose light has been speeding
toward us for 13 billion years.
Beyond that is the cosmic
background radiation...
from just 400,000 years
after the Big Bang.
In NASA's color-coded picture...
the radiation's glow is pure green...
representing a distribution
of matter so uniform...
its temperature varies no more
than 1/50,000th of a degree.
Nothing in human experience...
is even close to this
kind of uniformity.
In fact, astronomers
believe the universe
should really be very different.
By rights, the universe should be lumpy.
If you look in this direction
and you look in that direction...
you should see two entirely
different concentrations of matter...
different temperatures...
but it's extremely uniform.
Therefore, we have a puzzle.
The puzzle has its roots
at the universe's birth in the Big Bang.
If everything flew apart
from the beginning...
why shouldn't it be uniform?
No kind of explosion
that we know about...
leads to that kind of uniformity.
If you imagine an ordinary explosion-
an atomic bomb, a piece of TNT-
it's not really uniform at all.
There's a piece of
shrapnel going off there...
piece of paper going off there,
an extra piece of iron going off there.
It's really very non-uniform.
So scientists believe
the cosmic background radiation...
just shouldn't be as
smooth a green as it is.
We can find out why in
an ordinary paint store.
Let's consider a universe...
that consists of different
colored cans of paint.
In our hypothetical paint universe...
we have a can of yellow paint
and a can of blue paint...
and at the instant of
the Big Bang in this universe...
the two cans of paint start
expanding apart from each other.
In our hypothetical paint universe,
one side of it would look yellow...
and the other side would look blue.
But as we've learned,
the cosmos looks green...
whether it's the paint
universe or the real thing.
The two colors of paint represent
the different particles...
in the infant universe.
To end up a uniform green...
like the cosmic background radiation...
they had to be touching.
But when scientists first calculated
the speed of the Big Bang...
they concluded that it
blew everything apart...
faster than the speed of light...
meaning blue and yellow
were too far apart...
even at the instant of creation,
for any mixing to take place.
Seeing a universe that's so uniformly
green would be very strange.
It would be like taking
our can of yellow paint...
pouring it out, and having it be green.
Then taking a can of blue
paint, pouring it out...
and having it be green as well.
It's impossible.
This horizon problem can be solved...
by a theory that I've
worked on called inflation...
which is a twist on the Big Bang.
Inflation is now the widely
accepted variation...
that makes the Big Bang work...
without the limit imposed
by the speed of light.
Another way this could've happened
is that our paint universe...
might have expanded only this far.
The two cans of paint
have enough time to mix...
and become uniformly green...
before the universe undergoes
a sudden period of expansion...
that occurs faster
than the speed of light.
This would spread green
paint all over the universe.
If this theory is right...
the period of inflation is really
"the" Big Bang that we observe.
The other bang, that
happened before that...
becomes really a Little Bang.
It's just a precursor
to the real Big Bang.
Even today, the universe is
expanding at high velocity...
galaxies speeding away
from each other so fast...
that they seem to violate light
speed as the ultimate speed limit.
The faster-than-light
expansion of space...
sets yet another limit on
what we can see from Earth...
where the galaxies of the universe
continue to rush away from us.
The galaxies that are
relatively near to us...
those that you can see easily...
are moving away pretty fast...
and, indeed, the more distant
ones are moving away faster.
But the ones that are
really far away,
in fact, are moving away
faster than the speed of light.
And then there are the galaxies
that you will never see...
because they started out so far away...
that the light from them
will never reach you...
because the space is expanding
faster than the speed of light.
Space itself then is
the exception to the rule.
It can expand faster
than the speed of light.
But everything inside
it remains bound...
by Albert Einstein and
his theory of relativity.
Albert Einstein is the cop on the block.
You cannot break the light barrier.
We physicists can
accelerate particles...
to 99.9999 percent the speed of light...
but we have never, ever
broken the speed limit.
But we don't need to break the limit...
to experience the strange
province of light speed.
If the universe bends and stretches
around the speed of light...
what happens when we hit
the accelerator and start to get close?
For most of us, light seems
simple and uncomplicated...
a quality of nature by
which we see the universe.
Under the scrutiny
of science, however...
it becomes strange and bizarre.
Light is such a common thing
in our everyday experience...
and yet we have very little
understanding of it really.
It's very weird.
The speed of light is something...
that the entire universe
bends around to accommodate.
We can begin to understand...
why the universe bends
itself around light speed...
by joining physicist Clifford
Johnson at a bicycle track...
where a tennis ball will
compete against a beam of light.
If I throw an ordinary
object like a tennis ball...
I can throw it at a given speed,
it will go a certain distance.
This is the path of the tennis ball...
as Johnson throws it
while he's standing still.
It lands roughly halfway down the track.
Next, he'll throw the ball again...
but this time from a moving bike...
with different results.
If I throw the tennis
ball at that same speed...
while riding the bike,
it'll go faster...
because it's the speed
of the tennis ball...
plus the speed of the bike,
and so it'll go further.
Compare the two tosses,
and the difference is clear.
The ball goes faster and farther
when thrown from the moving bike.
It makes perfect sense.
But now we put light to the same test...
using the bike's headlight
instead of a tennis ball.
If I'm standing stationary...
and I switch
on the headlight of the bike...
that beam of light that
comes out of the headlight...
comes out at the speed of light...
no other speed but the speed of light.
Suppose the beam was slow enough...
for us to actually see
its motion down the track.
We mark its position
just a brief moment later.
Next, Johnson switches on
the headlight at riding speed...
and the unexpected happens.
In that same moment of time...
the light travels exactly
the same distance as before.
Unlike for the tennis ball...
you don't add the speed of
the bike to the speed of the light.
The speed of light
remains the speed of light.
The two light beams
travel the same distance...
because light speed is constant...
and independent of the source's motion.
It may fly against intuition,
but it is a fact of nature.
Every beam of light in the universe...
travels at the same
speed in empty space...
no matter how fast
the star or comet or galaxy...
that emits it is moving.
After scientists discovered this
fact at the end of the 19th century...
Albert Einstein did
the math for the rest of us...
and developed his special
theory of relativity...
with constant light speed as its center.
Understanding the speed of
light gave us a window...
into understanding
the nature of space and time...
as we understand it now.
We do not live in a rigid world...
where meter sticks and a clock
ticking at regular intervals.
We live in a flexible,
stretchy Einstein's world...
a relativistic world of space and time.
In common experience...
the universe doesn't seem
very stretchy to us...
because compared to light
speed, we are moving very slowly.
But when we crank up the
velocity, things begin to change.
As you get closer and closer
to the speed of light...
all sorts of strange and
marvelous distortions take place.
When we say that the universe
kind of bends itself...
so that the speed of
light is always constant...
it's amazing how literally
that's really true.
As you move closer and closer
to the speed of light...
your time appears to slow down...
to an observer that's just
sort of watching you go by.
That's amazing.
When Clifford Johnson
bikes around the track...
he needs to be going about
56 million times faster...
than his current 12 miles per hour...
to get close to light speed.
But suppose he could.
Imagine I were riding my bike
close to the speed of light.
Never mind whether
that's possible or not.
Just imagine that this was happening.
My clock's running slow...
compared to the cameraman on
the ground who's filming me.
If I do that for a while...
I'm going to age much more slowly...
than the cameraman who's on the ground.
So that when I come
back from the trip...
and come back and talk
to the cameraman...
he's actually much older
than when I left him.
If this sounds like magic
instead of science...
there is proof in something that
many of us experience every day.
A great example of Einstein's
special theory of relativity...
and the fact that clocks that are
moving relative to you run more slowly...
than your own clock, which
is at rest, is the GPS system.
The Global Positioning System lets us
drive our cars without getting lost.
Turn right.
GPS begins with a network
of 24 satellites...
orbiting the Earth 12,500
miles above the surface.
At any one time,
the device in your car...
receives signals from at
least four satellites...
and compares their light
speed travel times...
to calculate an accurate
location on the ground.
Drive 500 feet, then turn right.
The whole thing depends
on super accurate clocks.
And when the engineers
designed the system...
they knew the satellites
would be orbiting...
at nearly 7,000 miles an hour.
The speed is enough to
slow down their clocks...
by a tiny fraction of a second.
The engineers have factored all
the relativistic time differences...
into the system, which gives
it impressive precision.
If the clocks in the satellites
are running at a different rate...
than the clocks down here on Earth...
and you don't take that into account...
you will get the wrong
answer for where your car is.
Drive .1 mile to destination on left.
The distortion of time is only
one of the strange results...
of traveling close
to the speed of light.
On the bike track...
Clifford Johnson continues
to push the envelope...
as space begins doing odd
things to him and his bicycle.
Imagine I'm on my bike again,
going close to the speed of light.
An observer looking at me would
actually see, for example...
that the length of my bike in
the direction of motion I'm moving...
is getting shrunk.
Actually, the bike is getting shorter.
The effect is called
length contraction...
and together with time dilation...
it is seen by a stationary observer...
while looking at someone
traveling close to light speed.
But Professor Johnson
does get his own chance...
to witness light speed's weird effects.
As his velocity closes
in on light speed...
his view of the world
changes drastically.
What I'm seeing as I move close...
to the speed of light straight ahead...
is that the shapes in front of me...
are getting quite distorted
as compared to everyday life.
Everything is being twisted
into a sort of tunnel shape...
and the colors are getting
distorted in various ways.
The color changes come
from the Doppler effect...
and the shape distortions from
a phenomenon known as aberration.
The distortion is somewhat
similar to what you would see...
if you were driving through a rainstorm.
If you were stationary...
you would just see the rain
coming straight down...
if you looked out of
the side of the window.
Whereas, if you were
moving through the storm...
you would see that the rain appears
to be slanting towards you...
as a result of your motion.
And that's at the basis of that
warping effect that you get...
as you're moving near
the speed of light...
towards objects in front of you.
In reality, we don't have to
travel near the speed of light...
to experience the distortions...
caused by motion through time and space.
They are with us every
minute of the day.
All of the distortions that happen...
as a result of
a finite speed of light...
still happen on an everyday basis...
even in our everyday life...
but the effects are so tiny
that we can't perceive them.
Still, light speed
has its other quirks...
in the slow-moving world...
quirks we perceive very well.
The speed of light may be a constant...
but only in the vacuum of space.
When light moves through
things like glass or fluids...
it slows down appreciably.
If it didn't, things like telescopes
and human vision would be impossible.
But what would happen if
light slowed down much more...
if the speed of light were zero?
Light speed is 186,000 miles per second.
It is a universal constant,
but a constant with a catch.
It travels at that
speed only in a vacuum.
Light changes its speed when it
travels through different media.
It travels more slowly through water.
That's why you see
refraction and bending...
and rippling of light
when you're underwater.
Life as we know it would
be very different...
if light didn't propagate
at different speeds...
through different materials.
For example, we wouldn't be able to see.
Our eyes wouldn't work the same way.
In a universe where light
moved at the same speed...
through all materials...
we would know little of
the world around us...
seeing only vague
blobs of dark and light.
That's because our eyes
depend on biological lenses...
to focus images on our retinas.
Just like lenses made of glass...
they work because light slows
down as it passes through them.
Now why is that?
Because light is absorbed
by the atoms of glass...
and then they re-radiate it
later, so there's a delay factor.
Light hits an atom, the atom vibrates...
and then sends a light package off.
So there's a delay factor.
The delay factor also
causes light to bend...
when it hits glass shaped into a lens.
Bent in just the right way...
light can be focused,
collected, and magnified.
For astronomers studying the universe...
nothing could be more important.
Thank goodness light slows down
when it goes through glass...
because that's the reason
why we have telescopes.
The reason why we have telescopes...
is because light bends
going through glass...
and we can concentrate large
amounts of light to a single point...
and then that gives us the ability...
to see the marvels in
the universe itself.
Light travels through
the glass lenses of telescopes...
at about 124,000 miles per second...
two-thirds of its
speed through a vacuum.
But some scientists are looking
at making use of light...
at far slower speeds.
At her lab on the campus
of Harvard University...
Dr. Lene Hau has taken slow light...
to the extreme by reducing
light speed to zero.
The speed of light, of
course, is incredibly high.
I mean, nothing goes
faster than light...
and, you know, the usual
186,000 miles per second.
And we kind of thought,
gee, that's awfully high.
Let's try to do something about it.
Can we have the detector right there?
Hau and her team conducted
their experiments...
in a complex laboratory
filled with lasers, mirrors...
prisms, and other exotic gear.
It is a branch of physics
where few have dared to tread.
If you can start to change
things so dramatically...
as taking this enormous light speed...
and then bring it down
to bicycle speed...
then you're in a completely
new regime of nature.
You're able to now
start to probe areas...
regions of nature where nobody
has ever been there before.
The brakes are put on light
speed inside Hau's lab...
by focusing lasers on two
microscopic clouds of sodium gas...
chilled to a few billionths of
a degree above absolute zero.
A control laser hitting the two
clouds sets them up for action.
Then a quick light pulse
shoots into the first cloud...
where it is squeezed into the gas...
and slowed to just a few miles per hour.
The light pulse goes from being about
one kilometer long in free space.
It compresses like a concertina
as it enters the atom cloud...
and ends up being only
0.02 millimeter in size.
That's less than half
the thickness of a hair...
so really small.
And it's so small
that the light pulse...
actually ends up fitting
totally inside the atom cloud.
Hau says the atomic imprint
of light in the sodium cloud...
is a perfect copy embedded in atoms...
of the original light pulse.
It can then be stopped in free space...
between the two clouds before moving on.
When it enters the second cloud...
another shot of the control laser...
expands it to its
original size, shape...
and speed of 186,000 miles per second.
It is comparable in some ways to
a science fiction transporter...
that sends people or
objects through space.
So in these experiments
what we really do is...
we stop and extinguish a light
pulse in one part of space...
and revive it in a completely
different part of space...
and send it back on its way.
Since light can carry information...
this super-advanced
technology points the way...
to futuristic light-based computers...
that bypass wires and electronic chips.
Information read directly from light...
may be faster, more
compact, and more secure...
than anything we have today.
But the greatest vision of
scientists and dreamers...
is to be found at the other
end of the light speed spectrum.
We still face the speed of
light as an impenetrable wall...
a speed that Dr. Einstein told
us could never be exceeded.
Yet history is packed with
impossibles that have become realities.
Will we ever, for instance,
be able to reach the stars...
in ships that go faster
than the speed of light?
If so, when?
In April 2008, world-famous
physicist Stephen Hawking...
called on the human
race to colonize space...
and make interstellar
travel a long-term aim.
Spreading out into space...
will completely change
the future of the human race...
and maybe determine whether
we have any future at all.
The stars are so far away that
interstellar travel is impractical...
unless we can go faster
than light speed...
but that's an obstacle.
Einstein's theory of relativity...
tells us that a spaceship's mass...
approaches infinity as it
nears the speed of light.
So as you try to go to faster
and faster and faster...
you actually get to a point...
where it takes more and more energy...
until it's an infinite amount of
energy to go to speed of light.
That's impossible.
It means that travel at light
speed is also impossible.
Or is it?
Marc Millis is one of
a handful of scientists...
who isn't ready to throw
in the towel on the subject.
A NASA propulsion
physicist by profession...
he likes to build models of
starships in his spare time...
and is well aware of
the giggle factor...
in any talk outside science
fiction of star travel.
The giggle factor is
actually a healthy response.
It helps provide skepticism to
the topic to ask deep questions...
to make sure that we're
proceeding correctly.
Once head of NASA's mothballed
Breakthrough Propulsion Project...
Millis is editor of a book...
that has collected the serious
current research on the subject.
When it comes just to
the light speed issue...
there's about three dozen physicists...
who've written articles,
some skeptical...
some suggesting new
methods on the topic.
No one is saying that anytime soon...
we'll be able to have
warp drive to the stars.
But on a scale of
centuries to millennia...
it can't be ruled out.
Virtually all physicists agree...
it's impossible to
travel through space...
at faster than light speed.
But there may be a way to cheat...
by altering space instead
of traveling through it.
Believe it or not, even NASA scientists
are studying the possibility...
that perhaps we can fold
space, punch a hole in space...
make a subway system
through space and time.
That's the basic idea
behind using wormholes...
to actually twist space
around on itself...
and take a shortcut
through the universe.
What would a wormhole machine look like?
Probably huge in scale
with equipment staged...
perhaps on a massive
number of asteroids...
arranged in a gigantic sphere.
It would require an enormous
battery of laser beams...
that concentrate tremendous
energy to a single point.
You have to attain
fantastic temperatures...
the highest energy
attainable in our universe...
in order to open up a hole, a bubble...
a gateway perhaps to another universe.
Another way of tricking space...
into letting us travel faster
than light is the warp drive.
Miguel Alcubierre was the first one...
to write about the warp drive in 1994.
Alcubierre, a Mexican physicist,
worked out the math for a starship...
propelled by warping space-time itself.
Behind the ship,
space-time is expanded.
In front of the ship,
space-time contracts.
In between, the ship
rides like a surfer.
The ship itself sits inside a bubble...
and the space around it
pushes it faster than light.
A successful warp drive,
if it is possible at all...
is probably centuries away.
But in Switzerland, physicists
at the Large Hadron Collider...
may be headed in the right
direction right now.
Now, the Large Hadron
Collider is an atom smasher.
It's a particle collider.
But it's going to get to
high enough energies...
that space and time will
actually warp and bend.
We're actually practicing how
to bend space in the laboratory.
It's the first baby
step togward a warp drive.
With the physics we now know...
we won't travel faster
than light speed...
in the foreseeable future.
That doesn't mean we shouldn't try.
Even though light speed travel
might turn out to be impossible...
to give up without
trying is just giving up.
Outside his work at NASA...
Millis has founded the
nonprofit Tau Zero Foundation...
to encourage serious
research on star travel.
Although few scientists are
pursuing the idea actively...
many agree it's worth
at least the effort.
Understanding our universe...
is one of the most basic
needs human beings have...
as an intelligent species.
So should we pursue
technologies or physics...
that might allow us someday
to travel faster than light?
Absolutely.
Because we never know
where this might take us.
Even though we might
never discover a way...
to travel faster than light...
we might discover a whole bunch
of other very useful things.
And what if science ultimately proves...
the light speed barrier
is unbreakable...
and star travel is impossible?
It would put a whole new
perspective on spaceship Earth...
forcing us to use our
technology to treat it well...
as we remain its passengers...
on our continuing journey
through the universe.
and then... BANG!...
giving birth to an endless
expanding existence...
of time, space, and matter.
Now, see further than
we've ever imagined...
beyond the limits of our existence...
in a place we call "The Universe."
Streaking through space...
light is the fastest
thing in the universe.
It could circle the Earth
seven times in one second.
As it reaches us
across vast distances...
it reveals the history of the cosmos.
We're able to look back in time.
Light travels at
186,000 miles per second.
Its speed is an ultimate barrier.
Nothing can go faster.
We have never ever
broken the speed limit.
But is the answer final?
Will spaceships ever
speed faster than light?
Is it even worth trying?
To give up without
trying is just giving up.
It can neither be touched nor felt.
It is an abstract quantity
of immense impact...
the rate of motion at the very
heart of all existence.
The fundamental lynchpin
of the universe...
that we call light speed.
On planet Earth, where
speed is in demand...
the fastest people,
vehicles, and technologies...
seem to crawl in a cosmos
where light speed is king.
More than king, the speed of
light is the cornerstone...
on which the universe is built.
There's a famous saying in physics...
which is that the speed of light is
not just a good idea, it's the law.
The speed of light is one of
the most important speed limits...
in the entire universe.
The speed of light,
186,000 miles per second...
is just incredible.
I mean, if light traveled in
a circle around the Earth...
it could circle the Earth
seven times in one second.
That's an incredible speed.
That incredible speed is
the first thing we encounter...
when confronting
the phenomenon of light.
To say it is fast is
a colossal understatement.
It's amazing to me that when
I talk on my cell phone...
I can talk to somebody
clear across the country...
and I'm not really
aware of any time lag...
and that signal is going
from my phone to a tower...
up to a satellite, back down,
and it seems instantaneous.
So we really take for granted...
the speed of light could
practically be infinite to us.
Physics professor
Clifford Johnson of USC...
is an avid bike rider.
Circling a track, he
considers trying to cover...
the same 186,000 miles that
light does in one second.
He'll find, however, that his
work will be cut out for him.
To travel the distance that
light moves in just one second...
it would take me 22 months on a bike...
moving at 12 miles an hour,
cycling 24 hours a day.
But the speed of light,
in relation to the speed of life...
makes our world work in just
the way we've come to expect.
One of the beneficial
effects for humanity...
of having the speed of
light be as fast as it is...
is that what you see is what you get.
Light speed makes everyday
experience virtually instantaneous.
When the light bulb goes
on, you see it right away.
Anything that happens around
you registers immediately.
And certain experiences
make it crystal clear...
that light travels faster than
anything else, including sound.
One interesting consequence
of the great speed...
with which light travels is that
you see a flash of lightning...
essentially instantaneously...
but you hear the thunder only later on.
But light speed has its limits...
when stacked up to a place
as large as the universe.
We think that the speed of light...
is unimaginably fast on a human scale.
However, in astronomical terms,
it's actually kind of pokey.
And so it's ironic that when
the Apollo spacecraft blasted into space...
traveling at what seemed
an amazing 25,000 miles per hour...
the speed of light proved
frustratingly slow...
when it came time to
talk to astronauts...
236,000 miles away on the lunar surface.
So when the astronauts
were on the Moon...
and people asked Neil Armstrong...
"Hey, Neil, what's it like up there?"
Several seconds went by
between the question...
and Neil Armstrong's answer.
Neil, this is Houston.
Radio check, over.
Aye, roger, Houston, loud and clear.
- Roger out.
- Loud and clear, Houston.
Roger, Buzz.
And those several seconds...
were not because he was
thinking about the answer...
but rather because
it took 1.3 seconds...
for the signal traveling
at the speed of light...
to reach Neil from Mission Control...
and another 1.3 seconds for his reply...
using radio waves to come back...
and that's 2.6 seconds
without even thinking.
Okay.
The 1.3 seconds it takes light to
travel from the Earth to the Moon...
is pocket change compared
to other celestial bodies.
Light from the Sun, for instance...
takes more than eight
minutes to get to the Earth.
If the Sun were to
disappear right now...
if the Sun were to suddenly vanish...
it would take eight minutes...
before we would even
feel the shockwave...
and see the effects
of a disappearing sun.
The limits of light speed...
also make communicating with
Earth's far-flung spacecraft...
a special challenge.
It takes up to 44 minutes for
signals to travel back and forth...
to the probes exploring Mars...
more than three hours
to Cassini at Saturn...
and over 29 hours to Voyager 1,
the most distant of all...
now heading out of the solar system.
Still, these distances are
trivial on a cosmic scale.
We can almost understand
the 10 billion miles...
separating Earth from Voyager...
but what's next?
The nearest star is a red
dwarf named Proxima Centauri...
nearly 25 trillion miles away.
That's 25 followed by 12 zeroes.
I am often asked a question,
"How can you, as an astronomer...
"really comprehend these vast
distances, " these huge numbers?"
And the answer is, I can't.
The human brain really doesn't
wrap itself around numbers that big.
Occasionally, I actually write out...
how many zeroes there are in
kilometers from here to a galaxy...
just to see how huge that number is.
But in reality, of course,
as astronomers...
we would be spending
all day writing zeroes...
unless we came up with
a better unit to use...
and that's what a light-year is.
A light-year is approximately
6 trillion miles.
It's the distance that
light travels in one year.
Using light-years to
describe distances...
opens up another dimension
of light speed's character.
Think of it. Sirius,
the brightest star in the sky...
is 8.6 light-years away.
That means we see it,
not as it is today...
but as it was 8.6 years ago.
We see the bright star Vega
as it was 25 years ago...
and the red super giant
Betelgeuse as it was 500 years ago.
It's a wonderful gift of nature...
that because it takes time to travel,
we're able to look back in time.
The further out we look in distance,
the further back in time we look.
We would have no idea what
our cosmic history was...
if the speed of light
traveled instantaneously.
Laura Danly is curator of the historic
Griffith Observatory in Los Angeles.
With light's ability to
take us into the past...
she's assembled a stack of photos...
that tell light speed's story
of the universe in snapshots...
looking back in time to its beginning...
more than 13 billion years
ago to the present day.
I'm putting together a scrapbook...
of the history of our
family of galaxies...
and I chose all the galaxies that
we can see with our telescopes...
as far back as we can
see with our telescopes.
Each photo in this album, then,
shows something in the universe...
with a look-back time equivalent
to its distance in light-years.
The famous Crab Nebula,
6,500 years ago...
the Galactic Core,
center of the Milky Way...
26,000 years ago...
and the Andromeda galaxy,
our next-door neighbor...
2.5 million years ago...
but practically yesterday
on a cosmic scale.
I love this cluster.
For almost 90 percent
of the look-back time...
the album is filled
with common galaxies.
Common, yes, but intriguingly diverse.
And these two are colliding.
You can see one going...
what appears to be right
through the other...
and there's a lot of drama
in the way galaxies evolve...
and the way they
interact with one another.
So this one would be...
Oh, well, it's only about
500 million light-years away.
As Danly places each
shot in the album...
a bigger picture begins to emerge.
Adult galaxies have been
the main characters...
evolving in all their variety
for the past 12 billion years.
But the cosmos also has
its childhood photos...
showing galaxies when
the universe was a mere toddler.
These are actually very
interesting galaxies...
at about 11 billion light-years away.
These compact galaxies are-
Represent what might be
a 2 or 2 1/2-year-old child...
you know, just really
learning how to walk.
But even these galaxies have
their younger brothers and sisters.
This spectacular shot
shows a gravity lens...
a cluster of galaxies 2.2
billion light-years away...
that bends light, allowing us to
see much further in space and time.
The lens reveals a tiny speck...
identified as one of the earliest
galaxies we can see...
as it was 13 billion light-years ago...
still an infant in
the evolving universe.
Galaxies, when they were babies...
really don't have a lot of
distinguishable features.
They're kind of blobs.
They don't really have
a lot of structure.
The universe, as a whole,
was something of a blob...
at the beginning of its life, too.
What we see of that time are
the first light waves in history...
reaching us only now...
13.7 billion years after
they flashed into existence.
We see them in the picture of
an afterglow from the Big Bang...
and they are known today...
as the cosmic microwave
background radiation.
The cosmic microwave
background radiation...
is the most distant thing we can see.
It is, in a sense, the picture
of the baby upon delivery.
NASA's All-Sky Picture
reveals a glow...
that is uniform everywhere we can see...
the universe as it was in
a cosmic moment after its birth.
But here, our view
comes to a sudden halt.
What we can see of
the universe is limited...
not by the size or power
of our instruments...
but by the barrier
of light speed itself.
How can the fastest
thing in the universe...
make us blind to the infinity of space?
Knowing that light speed is
6 trillion miles per year...
gives us the light-year,
a convenient shorthand...
for talking about the huge
distances in the universe.
But it's just as
important to understand...
that light speed at 6
trillion miles per year...
is an ironclad constant.
The speed of light is so constant...
that the universe actually
changes everything...
so that you never see
it going any other speed.
So the speed of light really is
the measuring stick of the entire universe.
In fact, the constancy of light speed...
results in an amazing tool
for measuring distance...
in the vastness of space.
The tool is called red shift.
It happens as light between
galaxies travels at a fixed speed.
When the space between
the galaxies expands...
the light racing between
them gets stretched...
turning red in color.
As light goes from one
galaxy to another...
from a distant galaxy to
our own, for example...
that light gets stretched along
with the stretching of space...
and that causes intrinsically
short-wavelength light...
like blue light...
to gradually become
long-wavelength or redder light.
That fundamentally is the cause
of the red shift that we see...
in the spectra of galaxies.
How does the red shift turn
into a way to measure distance?
It's all because of an astonishing
discovery made in 1926...
at the Mount Wilson
Observatory outside Los Angeles.
Being up here on Mount Wilson
is always a thrill for me...
because it was actually
right here at this location...
that our view of
the universe entirely changed.
It was here that Edwin Hubble found
out the universe is expanding...
and that was an amazing thing.
He wasn't expecting it.
Nobody thought that was the case,
and it changed everything.
Seeing red shifts everywhere...
Hubble found that all of
the universe's galaxies...
were moving away from each other...
which we now know is caused by
the expansion of space itself.
As seen from the Earth...
a galaxy doesn't look
like it's moving away...
but we know that it is because
its light is red-shifted.
A galaxy moving away at low
speed has a slight red shift.
A galaxy moving faster
has a larger red shift.
But Hubble found that those
faster-moving galaxies...
are also farther away.
That meant the greater the red shift...
the more distant the galaxy.
By seeing how fast space is expanding...
and working the math backwards...
cosmologists have been able to
estimate the age of the universe.
Combine that with light speed...
and you have a major brain twister.
The universe is such a huge place...
that the light travel time
really becomes important to us.
We believe the universe began
about 13 1/2 billion years ago.
That means the farthest in
any direction we can look...
is 13 1/2 billion light-years.
There hasn't been enough time for
light to travel more than that.
It's called our light horizon...
a sphere 13 1/2 billion
light-years in all directions...
containing everything we can see.
But that's where the brain
twister comes in.
Does space end there?
We have no reason to believe
that the distance we can see...
is the entire size of the universe.
In fact, it might be
much bigger than that.
It's just that, with
light travel time...
that's all we can see.
That's our horizon.
So, consider this conundrum.
Astronomers in a galaxy at
one edge of our horizon...
can't possibly see any galaxies
on the other edge of our horizon...
but they can see galaxies...
13 1/2 billion light-years
in the other direction...
and so can astronomers at
the edge of their horizon...
and on and on, perhaps to infinity.
As for astronomers on Earth,
light speed has them trapped.
If we ask what is happening
beyond our light horizon...
we have to face the fact...
that the speed of light
really is a barrier.
We've never seen anything
beyond our light horizon.
Can we take comfort in the fact...
that there is so much to
see inside our horizon?
This breathtaking shot is the Hubble
Space Telescope's Ultra Deep Field.
It's a massively detailed
photo of an area of the sky...
a hundred times smaller
than the full Moon...
yet containing 10,000 galaxies...
some whose light has been speeding
toward us for 13 billion years.
Beyond that is the cosmic
background radiation...
from just 400,000 years
after the Big Bang.
In NASA's color-coded picture...
the radiation's glow is pure green...
representing a distribution
of matter so uniform...
its temperature varies no more
than 1/50,000th of a degree.
Nothing in human experience...
is even close to this
kind of uniformity.
In fact, astronomers
believe the universe
should really be very different.
By rights, the universe should be lumpy.
If you look in this direction
and you look in that direction...
you should see two entirely
different concentrations of matter...
different temperatures...
but it's extremely uniform.
Therefore, we have a puzzle.
The puzzle has its roots
at the universe's birth in the Big Bang.
If everything flew apart
from the beginning...
why shouldn't it be uniform?
No kind of explosion
that we know about...
leads to that kind of uniformity.
If you imagine an ordinary explosion-
an atomic bomb, a piece of TNT-
it's not really uniform at all.
There's a piece of
shrapnel going off there...
piece of paper going off there,
an extra piece of iron going off there.
It's really very non-uniform.
So scientists believe
the cosmic background radiation...
just shouldn't be as
smooth a green as it is.
We can find out why in
an ordinary paint store.
Let's consider a universe...
that consists of different
colored cans of paint.
In our hypothetical paint universe...
we have a can of yellow paint
and a can of blue paint...
and at the instant of
the Big Bang in this universe...
the two cans of paint start
expanding apart from each other.
In our hypothetical paint universe,
one side of it would look yellow...
and the other side would look blue.
But as we've learned,
the cosmos looks green...
whether it's the paint
universe or the real thing.
The two colors of paint represent
the different particles...
in the infant universe.
To end up a uniform green...
like the cosmic background radiation...
they had to be touching.
But when scientists first calculated
the speed of the Big Bang...
they concluded that it
blew everything apart...
faster than the speed of light...
meaning blue and yellow
were too far apart...
even at the instant of creation,
for any mixing to take place.
Seeing a universe that's so uniformly
green would be very strange.
It would be like taking
our can of yellow paint...
pouring it out, and having it be green.
Then taking a can of blue
paint, pouring it out...
and having it be green as well.
It's impossible.
This horizon problem can be solved...
by a theory that I've
worked on called inflation...
which is a twist on the Big Bang.
Inflation is now the widely
accepted variation...
that makes the Big Bang work...
without the limit imposed
by the speed of light.
Another way this could've happened
is that our paint universe...
might have expanded only this far.
The two cans of paint
have enough time to mix...
and become uniformly green...
before the universe undergoes
a sudden period of expansion...
that occurs faster
than the speed of light.
This would spread green
paint all over the universe.
If this theory is right...
the period of inflation is really
"the" Big Bang that we observe.
The other bang, that
happened before that...
becomes really a Little Bang.
It's just a precursor
to the real Big Bang.
Even today, the universe is
expanding at high velocity...
galaxies speeding away
from each other so fast...
that they seem to violate light
speed as the ultimate speed limit.
The faster-than-light
expansion of space...
sets yet another limit on
what we can see from Earth...
where the galaxies of the universe
continue to rush away from us.
The galaxies that are
relatively near to us...
those that you can see easily...
are moving away pretty fast...
and, indeed, the more distant
ones are moving away faster.
But the ones that are
really far away,
in fact, are moving away
faster than the speed of light.
And then there are the galaxies
that you will never see...
because they started out so far away...
that the light from them
will never reach you...
because the space is expanding
faster than the speed of light.
Space itself then is
the exception to the rule.
It can expand faster
than the speed of light.
But everything inside
it remains bound...
by Albert Einstein and
his theory of relativity.
Albert Einstein is the cop on the block.
You cannot break the light barrier.
We physicists can
accelerate particles...
to 99.9999 percent the speed of light...
but we have never, ever
broken the speed limit.
But we don't need to break the limit...
to experience the strange
province of light speed.
If the universe bends and stretches
around the speed of light...
what happens when we hit
the accelerator and start to get close?
For most of us, light seems
simple and uncomplicated...
a quality of nature by
which we see the universe.
Under the scrutiny
of science, however...
it becomes strange and bizarre.
Light is such a common thing
in our everyday experience...
and yet we have very little
understanding of it really.
It's very weird.
The speed of light is something...
that the entire universe
bends around to accommodate.
We can begin to understand...
why the universe bends
itself around light speed...
by joining physicist Clifford
Johnson at a bicycle track...
where a tennis ball will
compete against a beam of light.
If I throw an ordinary
object like a tennis ball...
I can throw it at a given speed,
it will go a certain distance.
This is the path of the tennis ball...
as Johnson throws it
while he's standing still.
It lands roughly halfway down the track.
Next, he'll throw the ball again...
but this time from a moving bike...
with different results.
If I throw the tennis
ball at that same speed...
while riding the bike,
it'll go faster...
because it's the speed
of the tennis ball...
plus the speed of the bike,
and so it'll go further.
Compare the two tosses,
and the difference is clear.
The ball goes faster and farther
when thrown from the moving bike.
It makes perfect sense.
But now we put light to the same test...
using the bike's headlight
instead of a tennis ball.
If I'm standing stationary...
and I switch
on the headlight of the bike...
that beam of light that
comes out of the headlight...
comes out at the speed of light...
no other speed but the speed of light.
Suppose the beam was slow enough...
for us to actually see
its motion down the track.
We mark its position
just a brief moment later.
Next, Johnson switches on
the headlight at riding speed...
and the unexpected happens.
In that same moment of time...
the light travels exactly
the same distance as before.
Unlike for the tennis ball...
you don't add the speed of
the bike to the speed of the light.
The speed of light
remains the speed of light.
The two light beams
travel the same distance...
because light speed is constant...
and independent of the source's motion.
It may fly against intuition,
but it is a fact of nature.
Every beam of light in the universe...
travels at the same
speed in empty space...
no matter how fast
the star or comet or galaxy...
that emits it is moving.
After scientists discovered this
fact at the end of the 19th century...
Albert Einstein did
the math for the rest of us...
and developed his special
theory of relativity...
with constant light speed as its center.
Understanding the speed of
light gave us a window...
into understanding
the nature of space and time...
as we understand it now.
We do not live in a rigid world...
where meter sticks and a clock
ticking at regular intervals.
We live in a flexible,
stretchy Einstein's world...
a relativistic world of space and time.
In common experience...
the universe doesn't seem
very stretchy to us...
because compared to light
speed, we are moving very slowly.
But when we crank up the
velocity, things begin to change.
As you get closer and closer
to the speed of light...
all sorts of strange and
marvelous distortions take place.
When we say that the universe
kind of bends itself...
so that the speed of
light is always constant...
it's amazing how literally
that's really true.
As you move closer and closer
to the speed of light...
your time appears to slow down...
to an observer that's just
sort of watching you go by.
That's amazing.
When Clifford Johnson
bikes around the track...
he needs to be going about
56 million times faster...
than his current 12 miles per hour...
to get close to light speed.
But suppose he could.
Imagine I were riding my bike
close to the speed of light.
Never mind whether
that's possible or not.
Just imagine that this was happening.
My clock's running slow...
compared to the cameraman on
the ground who's filming me.
If I do that for a while...
I'm going to age much more slowly...
than the cameraman who's on the ground.
So that when I come
back from the trip...
and come back and talk
to the cameraman...
he's actually much older
than when I left him.
If this sounds like magic
instead of science...
there is proof in something that
many of us experience every day.
A great example of Einstein's
special theory of relativity...
and the fact that clocks that are
moving relative to you run more slowly...
than your own clock, which
is at rest, is the GPS system.
The Global Positioning System lets us
drive our cars without getting lost.
Turn right.
GPS begins with a network
of 24 satellites...
orbiting the Earth 12,500
miles above the surface.
At any one time,
the device in your car...
receives signals from at
least four satellites...
and compares their light
speed travel times...
to calculate an accurate
location on the ground.
Drive 500 feet, then turn right.
The whole thing depends
on super accurate clocks.
And when the engineers
designed the system...
they knew the satellites
would be orbiting...
at nearly 7,000 miles an hour.
The speed is enough to
slow down their clocks...
by a tiny fraction of a second.
The engineers have factored all
the relativistic time differences...
into the system, which gives
it impressive precision.
If the clocks in the satellites
are running at a different rate...
than the clocks down here on Earth...
and you don't take that into account...
you will get the wrong
answer for where your car is.
Drive .1 mile to destination on left.
The distortion of time is only
one of the strange results...
of traveling close
to the speed of light.
On the bike track...
Clifford Johnson continues
to push the envelope...
as space begins doing odd
things to him and his bicycle.
Imagine I'm on my bike again,
going close to the speed of light.
An observer looking at me would
actually see, for example...
that the length of my bike in
the direction of motion I'm moving...
is getting shrunk.
Actually, the bike is getting shorter.
The effect is called
length contraction...
and together with time dilation...
it is seen by a stationary observer...
while looking at someone
traveling close to light speed.
But Professor Johnson
does get his own chance...
to witness light speed's weird effects.
As his velocity closes
in on light speed...
his view of the world
changes drastically.
What I'm seeing as I move close...
to the speed of light straight ahead...
is that the shapes in front of me...
are getting quite distorted
as compared to everyday life.
Everything is being twisted
into a sort of tunnel shape...
and the colors are getting
distorted in various ways.
The color changes come
from the Doppler effect...
and the shape distortions from
a phenomenon known as aberration.
The distortion is somewhat
similar to what you would see...
if you were driving through a rainstorm.
If you were stationary...
you would just see the rain
coming straight down...
if you looked out of
the side of the window.
Whereas, if you were
moving through the storm...
you would see that the rain appears
to be slanting towards you...
as a result of your motion.
And that's at the basis of that
warping effect that you get...
as you're moving near
the speed of light...
towards objects in front of you.
In reality, we don't have to
travel near the speed of light...
to experience the distortions...
caused by motion through time and space.
They are with us every
minute of the day.
All of the distortions that happen...
as a result of
a finite speed of light...
still happen on an everyday basis...
even in our everyday life...
but the effects are so tiny
that we can't perceive them.
Still, light speed
has its other quirks...
in the slow-moving world...
quirks we perceive very well.
The speed of light may be a constant...
but only in the vacuum of space.
When light moves through
things like glass or fluids...
it slows down appreciably.
If it didn't, things like telescopes
and human vision would be impossible.
But what would happen if
light slowed down much more...
if the speed of light were zero?
Light speed is 186,000 miles per second.
It is a universal constant,
but a constant with a catch.
It travels at that
speed only in a vacuum.
Light changes its speed when it
travels through different media.
It travels more slowly through water.
That's why you see
refraction and bending...
and rippling of light
when you're underwater.
Life as we know it would
be very different...
if light didn't propagate
at different speeds...
through different materials.
For example, we wouldn't be able to see.
Our eyes wouldn't work the same way.
In a universe where light
moved at the same speed...
through all materials...
we would know little of
the world around us...
seeing only vague
blobs of dark and light.
That's because our eyes
depend on biological lenses...
to focus images on our retinas.
Just like lenses made of glass...
they work because light slows
down as it passes through them.
Now why is that?
Because light is absorbed
by the atoms of glass...
and then they re-radiate it
later, so there's a delay factor.
Light hits an atom, the atom vibrates...
and then sends a light package off.
So there's a delay factor.
The delay factor also
causes light to bend...
when it hits glass shaped into a lens.
Bent in just the right way...
light can be focused,
collected, and magnified.
For astronomers studying the universe...
nothing could be more important.
Thank goodness light slows down
when it goes through glass...
because that's the reason
why we have telescopes.
The reason why we have telescopes...
is because light bends
going through glass...
and we can concentrate large
amounts of light to a single point...
and then that gives us the ability...
to see the marvels in
the universe itself.
Light travels through
the glass lenses of telescopes...
at about 124,000 miles per second...
two-thirds of its
speed through a vacuum.
But some scientists are looking
at making use of light...
at far slower speeds.
At her lab on the campus
of Harvard University...
Dr. Lene Hau has taken slow light...
to the extreme by reducing
light speed to zero.
The speed of light, of
course, is incredibly high.
I mean, nothing goes
faster than light...
and, you know, the usual
186,000 miles per second.
And we kind of thought,
gee, that's awfully high.
Let's try to do something about it.
Can we have the detector right there?
Hau and her team conducted
their experiments...
in a complex laboratory
filled with lasers, mirrors...
prisms, and other exotic gear.
It is a branch of physics
where few have dared to tread.
If you can start to change
things so dramatically...
as taking this enormous light speed...
and then bring it down
to bicycle speed...
then you're in a completely
new regime of nature.
You're able to now
start to probe areas...
regions of nature where nobody
has ever been there before.
The brakes are put on light
speed inside Hau's lab...
by focusing lasers on two
microscopic clouds of sodium gas...
chilled to a few billionths of
a degree above absolute zero.
A control laser hitting the two
clouds sets them up for action.
Then a quick light pulse
shoots into the first cloud...
where it is squeezed into the gas...
and slowed to just a few miles per hour.
The light pulse goes from being about
one kilometer long in free space.
It compresses like a concertina
as it enters the atom cloud...
and ends up being only
0.02 millimeter in size.
That's less than half
the thickness of a hair...
so really small.
And it's so small
that the light pulse...
actually ends up fitting
totally inside the atom cloud.
Hau says the atomic imprint
of light in the sodium cloud...
is a perfect copy embedded in atoms...
of the original light pulse.
It can then be stopped in free space...
between the two clouds before moving on.
When it enters the second cloud...
another shot of the control laser...
expands it to its
original size, shape...
and speed of 186,000 miles per second.
It is comparable in some ways to
a science fiction transporter...
that sends people or
objects through space.
So in these experiments
what we really do is...
we stop and extinguish a light
pulse in one part of space...
and revive it in a completely
different part of space...
and send it back on its way.
Since light can carry information...
this super-advanced
technology points the way...
to futuristic light-based computers...
that bypass wires and electronic chips.
Information read directly from light...
may be faster, more
compact, and more secure...
than anything we have today.
But the greatest vision of
scientists and dreamers...
is to be found at the other
end of the light speed spectrum.
We still face the speed of
light as an impenetrable wall...
a speed that Dr. Einstein told
us could never be exceeded.
Yet history is packed with
impossibles that have become realities.
Will we ever, for instance,
be able to reach the stars...
in ships that go faster
than the speed of light?
If so, when?
In April 2008, world-famous
physicist Stephen Hawking...
called on the human
race to colonize space...
and make interstellar
travel a long-term aim.
Spreading out into space...
will completely change
the future of the human race...
and maybe determine whether
we have any future at all.
The stars are so far away that
interstellar travel is impractical...
unless we can go faster
than light speed...
but that's an obstacle.
Einstein's theory of relativity...
tells us that a spaceship's mass...
approaches infinity as it
nears the speed of light.
So as you try to go to faster
and faster and faster...
you actually get to a point...
where it takes more and more energy...
until it's an infinite amount of
energy to go to speed of light.
That's impossible.
It means that travel at light
speed is also impossible.
Or is it?
Marc Millis is one of
a handful of scientists...
who isn't ready to throw
in the towel on the subject.
A NASA propulsion
physicist by profession...
he likes to build models of
starships in his spare time...
and is well aware of
the giggle factor...
in any talk outside science
fiction of star travel.
The giggle factor is
actually a healthy response.
It helps provide skepticism to
the topic to ask deep questions...
to make sure that we're
proceeding correctly.
Once head of NASA's mothballed
Breakthrough Propulsion Project...
Millis is editor of a book...
that has collected the serious
current research on the subject.
When it comes just to
the light speed issue...
there's about three dozen physicists...
who've written articles,
some skeptical...
some suggesting new
methods on the topic.
No one is saying that anytime soon...
we'll be able to have
warp drive to the stars.
But on a scale of
centuries to millennia...
it can't be ruled out.
Virtually all physicists agree...
it's impossible to
travel through space...
at faster than light speed.
But there may be a way to cheat...
by altering space instead
of traveling through it.
Believe it or not, even NASA scientists
are studying the possibility...
that perhaps we can fold
space, punch a hole in space...
make a subway system
through space and time.
That's the basic idea
behind using wormholes...
to actually twist space
around on itself...
and take a shortcut
through the universe.
What would a wormhole machine look like?
Probably huge in scale
with equipment staged...
perhaps on a massive
number of asteroids...
arranged in a gigantic sphere.
It would require an enormous
battery of laser beams...
that concentrate tremendous
energy to a single point.
You have to attain
fantastic temperatures...
the highest energy
attainable in our universe...
in order to open up a hole, a bubble...
a gateway perhaps to another universe.
Another way of tricking space...
into letting us travel faster
than light is the warp drive.
Miguel Alcubierre was the first one...
to write about the warp drive in 1994.
Alcubierre, a Mexican physicist,
worked out the math for a starship...
propelled by warping space-time itself.
Behind the ship,
space-time is expanded.
In front of the ship,
space-time contracts.
In between, the ship
rides like a surfer.
The ship itself sits inside a bubble...
and the space around it
pushes it faster than light.
A successful warp drive,
if it is possible at all...
is probably centuries away.
But in Switzerland, physicists
at the Large Hadron Collider...
may be headed in the right
direction right now.
Now, the Large Hadron
Collider is an atom smasher.
It's a particle collider.
But it's going to get to
high enough energies...
that space and time will
actually warp and bend.
We're actually practicing how
to bend space in the laboratory.
It's the first baby
step togward a warp drive.
With the physics we now know...
we won't travel faster
than light speed...
in the foreseeable future.
That doesn't mean we shouldn't try.
Even though light speed travel
might turn out to be impossible...
to give up without
trying is just giving up.
Outside his work at NASA...
Millis has founded the
nonprofit Tau Zero Foundation...
to encourage serious
research on star travel.
Although few scientists are
pursuing the idea actively...
many agree it's worth
at least the effort.
Understanding our universe...
is one of the most basic
needs human beings have...
as an intelligent species.
So should we pursue
technologies or physics...
that might allow us someday
to travel faster than light?
Absolutely.
Because we never know
where this might take us.
Even though we might
never discover a way...
to travel faster than light...
we might discover a whole bunch
of other very useful things.
And what if science ultimately proves...
the light speed barrier
is unbreakable...
and star travel is impossible?
It would put a whole new
perspective on spaceship Earth...
forcing us to use our
technology to treat it well...
as we remain its passengers...
on our continuing journey
through the universe.