What would we see at the speed of light?

Optical effects of acceleration 02:22

• As the spaceship accelerates, a phenomenon known as the aberration of light occurs
• Light rays from the stars appear to come more from the front, causing the sky to contract before us
• This effect is perfectly analogous to raindrops on a car windshield
• This is due to the fact that the spaceship is moving in a different direction than the incoming light rays
• The aberration of light results in another phenomenon called the Terrell-Penrose rotation
• Images of objects seem contracted in front of us due to the spaceship's high speed

Doppler effect in space 04:39

• The Doppler effect occurs when the wavelength of light changes as a result of motion
• Looking out from the spaceship, the same phenomenon is at work as we move away from Earth
• The planet's light takes longer to reach us as we move away from it
• If we could zoom in with a telescope, we would see people on Earth evolving in slow motion
• Each tick of the clocks on Earth takes longer and longer to reach us
• The intensity of the light seems to weaken as the image of the planet shifts towards a red color
• In front of us, the opposite effect occurs as the ship catches up with light and the stars seem to get brighter and shift towards a blue color

Time dilation 06:40

• Time dilation is a consequence of special relativity
• The universe is a huge four-dimensional fabric called space-time, made up of three dimensions of space and one dimension of time
• When we picked up speed and zoomed away from Earth faster, our trajectory gradually deviated from that of the planet
• The axis we call time is no longer aligned with the time axis of people on Earth
• If we decided to turn around and come back, our clocks would have measured a different time
• We would have aged less than Earthlings because our trajectories in space-time would have been different

Length contraction 07:45

• Length contraction is another key consequence of special relativity
• When a body moves close to light speed, its length gets contracted in the direction of its motion
• From the spaceship's perspective, the entire universe is moving backwards
• The universe is contracted along our direction of motion
• The length of the journey to reach our destination is shorter than expected
• If we tried to reach a distant star, the journey would genuinely seem shorter to us
• It would take less and less time the faster we move

Length Contraction 08:54

• Length contraction is a real phenomenon.
• The farther we look into space, the farther we look into the past.
• When we cross the orbit of a planet that moves quickly towards us, the planet's length is contracted.
• The back of the planet is located further in space than the front of the planet.
• The image we receive from the back of the planet has taken longer to reach us, so we see it as it was in the past.
• Even if the planet is contracted, it would not look like it because we receive the image of its back with a delay.
• Rather than contracted, it appears to be rotated.

Terrell-Penrose Rotation 09:50

• Terrell-Penrose rotation is a phenomenon we have already seen.
• When we move very fast and look to our side, the edges of the objects around us seem shorter in the direction of motion.
• This can be interpreted either as length contraction or as a rotation change in perspective.
• A person watching us zoom by would not really see our ship contracted but rather rotated on itself.

Approaching the Speed of Light 10:25

• Over time, our field of view continues to contract.
• By accelerating more, we would perhaps expect to reach the speed of light at some point.
• However, it is strictly impossible to exceed or even reach the speed of light.
• Even if a ship accelerates constantly, it will never reach the speed of light.
• That is because the speed of light is absolute.
• No matter how much we accelerate, light escapes inexorably.
• Almost at light speed, all optical effects would become extreme.
• In our frame of reference, the universe would be extremely contracted like a thin fabric that we would cross from side to side in a fraction of a second.
• For a person on Earth, we would be moving at the speed of light, but for us, the trip seems instantaneous.
• We move infinitely fast.

The Warp Drive 12:28

• Nothing can ever move faster than light through space, but there might be a way to circumvent this rule.
• In fact, nothing prohibits space itself from moving faster than light.
• We could imagine creating a bubble around our spaceship which we would propel faster than light.
• This is called a warp drive in reference to science fiction.
• It would no longer be a matter of zooming a vehicle through space but of propelling the fabric of space itself.
• Our ship would remain motionless, surfing on a wave of faster-than-light space-time.
• Such a structure may seem absurd and indeed it is currently thought to be impossible to achieve.
• Producing a warp drive would require bending space-time with huge amounts of negative mass, a form of matter that does not seem to exist in our universe.
• That said, mathematics still allow us to model and calculate what we would see in such a situation.

What We Would See at the Speed of Light 13:14

• If we looked from outside the warp drive, it would seem to appear out of nowhere.
• The curvature of space-time deviates the trajectory of light rays, forming a moving lens which splits into two.
• One part moves forwards and the other retreats in the opposite direction.
• Light travels slower than the warp drive itself, and when it approaches, light has not yet had the time to reach us.
• After it crosses us, we receive both the light which had not yet reached us and the rays which were emitted later.
• Looking from the inside of the warp drive, we would see the sky contracted in front of us and very bright behind us.
• The universe would look extremely dark, and a whole patch of the sky would simply vanish from our view.
• The light emitted from there is too slow to catch up with us, and a cone of the universe remains permanently invisible.