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)
