Translator: Ilse S. Úziel Reviewer: Sebastian Betti
I want to ask you something:
When was the last time you watched the stars?
I know most people forget they exist
specially in this polluted city
which is sometimes foggy,
we never see them.
But since I was a kid, maybe not that young,
maybe 12 or 13 years,
I've been captivated by stars and would watch them whenever possible.
My dad gave me a small telescope
by the time I was 14 and I spent hours
watching planets and stars
and always wondering:
What is out there?
Is there someone watching me back
with a telescope, wondering what is out here?
This allure went on for years
and at some point I decided to be an astronomer.
In Mexico, in order to be an astronomer you need to be a physicist.
So I studied physics.
I never got to be an astronomer, now I'm something in between,
half an astrophysicist, half a physicist
but this idea of stars
and the possibility of reaching them
remained with me.
When I started my major in physics
I realized something many of you
have heard of, even if you are not totally clear about it:
that more than 100 years ago, in 1905,
this guy named Albert Einstein,
discovered that light speed
is the fastest in the universe.
That might not say you a lot
because light speed is huge.
Light moves up to 186,000 mi/s
so high a speed that we can phone call
someone in India or Japan
with no problem at all.
Even astronauts who went to the moon 40 years ago
were interviewed and the President could talk to them
with no evident delay
even though the astronauts were in the moon,
thing is that light speed is huge
and the universe gigantic.
We cannot travel faster than light speed
and that is a severe problem
to reach for the stars.
Sun is 8 light-minutes away,
that is, it takes 8 minutes for light
to get here from the Sun, from the Sun to us.
If the Sun exploded right now,
nobody would notice up until eight minutes later.
The closest star after the Sun
is Alfa Centauri,
it takes four years for light to travel
and it's right besides the Sun.
We live in a galaxy
that is a star spiral called Milky Way.
The center of our galaxy was 30,000 light years away,
it takes 30,000 light years for light to travel
from the center of the galaxy to us,
and two million years
in traveling from Andromeda galaxy
that is one of our neighbor galaxies.
The universe is huge, vast,
if we ever want to reach the stars
the light limit is very serious,
a very serious problem, but why?
Why we cannot travel faster than light?
And it's not because Einstein said so,
that is no how science works.
In science there is no authority principle;
it's not because some famous guy says so.
There are reasons, theoretical reasons,
observational reasons,
experiments show it,
it is a verified fact,
but why?
Basically, the answer is that theory of relativity prevents it,
so I will tell you a bit,
a very quick course:
Relativity in a couple of minutes.
Don't be afraid, I'll give a general overview,
normally it takes six months to teach this
to sixth and seventh graders of physics major.
So right now I will explain it
in two minutes and for non-physicists.
So, don't worry.
Relativity is an old concept
though it wasn't called like that.
The concept can be traced back from Galileo Galilei
around 1620, in the 17th century.
Galileo was the first one to realize something interesting,
when it comes to movement, when I move,
my movement is always relative to something else.
Movement is said to be relative,
here on the stage, my movement is relative to the floor.
The measurement of your car speed is relative to the street,
actually planes speed measurement
is made relative to the air, not the floor.
You might have noticed this while watching a movie.
A plane speed measurement is relative to the air,
and the Earth spins around the Sun, etc.
If you were somewhere in space
in the middle of nowhere it would be useless
to ask if you are moving or not
because there is no reference to compare your position,
so movement is relative, speeds are relative,
because they are always measured in relation to something else.
This was discovered by Galileo 400 years ago.
That was an interesting fact
for all physic studies made after Galileo.
Newton and all great advances of the 18th and 19th centuries
agreed with Galileo.
Speed is relative, that's fine,
speeds aren't absolute.
But by the end of 19th century something strange happened,
many physicists studying light
discovered that light is quite weird,
light speed is indeed absolute
and though Galileo stated that speeds were relative,
that's not the case of light, it's always the same number
no matter who measures it,
or how fast is going whoever is measuring,
no matter how fast the lightbulb sending out the light is moving.
The measurement always yields the same number
and this was a problem.
This might not seem interesting to you
but physicists of the 19th century were going crazy.
Problem was: either Galileo was wrong
and speeds were indeed absolute,
which was apparently nonsense;
or those who were measuring light speed
were wrong and didn't know how to measure.
But nobody was wrong
which was even worst.
Decades went by,
until in 1905 this guy appeared,
a man called Albert Einstein,
who devoted his life to bringing together
Galileo's idea that speeds were relative
and the apparently real fact
shown by the experiments, that there was an absolute speed,
light speed.
Long story short,
because math is complicated,
part of Einstein genius
was realizing there was a solution.
There was a logical solution to the problem
and that logical solution derived in what we now know
as Einstein's theory of relativity.
It's a very interesting theory that changes
what we understand by space and time,
for instance, nobody tells us that space is relative
distances, object lengths
depend on their movement; if an object moves fast, they shrink.
Time is also relative,
any watch ticking relative to my movement, would delay
this we have measured many times,
even worst: simultaneity is relative;
when I say two things happen exactly at once,
someone moving in relation to me would disagree.
One of us sees something first and worst:
we might be moving on opposed directions
and watch things backwards:
first this one, then that one.
So the conclusion is that sometimes,
the order in time of different things
is not absolute, the order of time can change,
one thing before, other thing after
but this brings up another huge problem,
if time order is not well defined, what about causality?
If something causes something else
that something should had happened first,
but if we disagree on what happened first,
where does that leaves causality?
Another crisis.
Part of what Einstein did
was realizing that there was solution,
a solution to protect causality
was thinking that light speed is not absolute,
but the maximum speed of universe.
If nothing can travel faster than light we protect causality.
If something could travel faster than light
then we could travel to the past,
we would be able to see the effect before the cause,
which is not the proper way.
So light speed is the maximum speed
and that is to protect causality.
So far as of the beginning of the 20th century,
light speed was the fastest
and if that was all left to say, my talk would be done
and off we go.
But, fortunately that's not the case.
In 1916, Einstein developed a second theory,
also called relativity and that's why people get confused
this one is called general relativity,
and it's a theory about gravity.
Einstein tried to understand gravity,
which we already understood a bit since Newton;
but he noticed some problems,
gravity was thought of by Newton as instantaneous,
if someone moved the Sun, Earth would immediately react,
this would go against the fact that nothing can travel faster than light,
so Einstein began to develop a new gravity theory,
it took him 10 years,
an amazing achievement for someone as smart of Einstein,
was based on a beautiful thing:
the Equivalence Principle, also discovered by Galileo:
all objects fall at the same speed
if two things were dropped at once, they would fall at the same time,
a bowling ball or a ping pong ball would fall just the same,
the heavier one does not fall faster, in case you were wondering.
That means, from another point of view,
that the trajectory of an object when there is gravity,
does not depend on the object.
All objects follow the same trajectory
curved trajectories, you've seen that,
I throw objects and they move in parables and ellipses
but if those trajectories are curve and nondependent of the object
then trajectory is a property of space, but they are curve,
then space must be curve.
Einstein concluded
that gravity is a space deformation.
An interesting and beautiful thing,
and what is beautiful about it is that I can cheat,
I can use space deformation
to cheat on Einstein himself,
so I use Einstein to cheat on Einstein.
I can imagine ways to distort space
to work around the statement "nothing can go faster than light"
and, technically, I could reach a faraway star
and then come back in time for dinner.
I will share with you two possibilities,
that are allowed on Einstein theory,
one is beautiful
and its technical name is Einstein-Rosen bridge,
sounds technical because Einstein
and another scientist called Rosen
had this idea in 1935.
But in literature and on sci-fi movies
it is called a Wormhole.
If you like science fiction then you might have seen it recently,
in the movie Interstellar.
On the movie, they travel through a wormhole.
A wormhole is like a tunnel,
I enter here and I end up in Alpha Centauri,
but traveling a shorter distance,
like a shortcut in space.
These structures --
here is a beautiful diagram of a wormhole in two dimensions --
are allowed by the Einstein's theory,
because this theory allows these tunnels,
one thing is that the theory allows it
and another is having an idea of how to do that.
Nobody knows how to make a wormhole,
but at least theory allows it.
Another idea, and I'll let you think about it,
another idea is that it is not necessary to make holes in space,
an idea that thought by some guy not so long ago,
in 1994, this guy on the picture,
and the idea is different; instead of making holes in space
let's use another property of space.
Space can bended, twisted and expanded,
maybe you heard about how universe expands,
galaxies move away from one another
not because they are drifting away from a center
where an explosion occurred, no.
The way we understand it in physics is that galaxies are still,
and what is growing bigger is space; space is expanding.
So I can use this idea in a small scale.
Imagine I'm standing here and somehow
I can expand the space behind me.
I would start to drift away from that wall,
and if at the same time I shrink the space in front of me
I would become closer to the wall in front of me.
If I combine the expansion and contraction,
I could move from here to that wall without moving,
because the space made all the moving.
This is called warp drive or drive through distortion
and it's another way to travel faster than light,
actually you could travel as fast as you wish.
These are two ideas on how we could travel faster than light.
But there is a price to pay.
Such is life, whenever you find something cool
it's too expensive.
We have a similar case here:
from those two ideas,
both worm holes and warp propulsion
require, whenever we do the math of something
called negative energy, which might not be crystal clear for you,
but remember what Einstein said:
"mass and energy are equivalent", the same thing.
Remember nuclear reactors and atomic bombs,
mass and energy are the same.
So negative energy equals negative mass,
and I'd never went to buy minus 9 pounds of tortilla.
There are no negative masses,
without negative masses there are no negative energies
and without negative energies none of this is possible,
No holes in space-time,
no warp propulsion,
and that's a problem.
Negative energy is not forbidden,
physics laws don't forbid it,
but we've never seen it.
It's one of those things that simply do not exist.
So, with this initial question:
Can we travel faster than light?
will we someday travel the stars and get back in time for dinner?
In 1905 Einstein told us it was not possible,
that light speed was a limit,
but sometimes, using Einstein's other theory,
general relativity, we can cheat and bend the space,
expand it, compress it, make holes on it,
and travel faster than light,
however, the price of it
is finding energies or negative masses,
though they might not exist.
So we are a bit stuck,
but such is science and that's part of my message,
science moves forward by making questions,
and sometimes we find answers,
sometimes we find answers we don't like,
that aren't what we wanted, but universe is not how we want it.
It is what it is and we sometimes find out
that we don't have enough information,
to answer the question,
and that is our current situation.
Currently, we do not have all the information.
Luckily, in 20, 30 or 100 years someone will come
and find the answer and tell us for once
if we can reach the stars faster than light speed.
Before I go I will ask you to do something,
tonight, if clouds allow it, please go out
and take a look of the stars
and think, what is out there?
Thank you so much.
(Applause)