Say I'm sitting on the bridge of a spaceship travelling N-times the speed of light. I'm facing forward. What do I see? Am I blinded because photons from far off stars are hitting my eyes at an increased rate?
Also, if I look to the left and the right, and behind me? What do I see ?
In Star Trek, it's all stripy-stars, and I'm sure that's not correct.
But what you can do is imagine what would happen if you reached the speed of light.
Length contraction means that while you and your ship appear to be the normal size, the universe around you shrinks along the direction of travel. The faster you go, the less distance there is in front and behind you. At the speed of light, the entire width of the universe shrinks to zero.
Also, you are at the same time experiencing time dilation. Although time on board your ship advances at the normal rate, time outside the ship appears to slow down. When you reach the speed of light, the rate of time passing outside the ship goes completely to zero.
Together these mean that the universe outside your ship effectively vanishes! It occupies no volume, and has no events in it. At the speed of light, your current position and your destination are the _same place_, because there is no distance and no time separating them.
This is why you cannot go faster than the speed of light. There aren’t any speeds faster than that.
This video takes a round–about route to get there, but it has a nice visualization: https://www.youtube.com/watch?v=HU6t8QvGZmA
This idea that special relativity cannot handle acceleration or accelerated frames often comes up in the context of the twin paradox, when people claim that it can only be resolved in general relativity because of the acceleration present. Their claim is wrong."
https://math.ucr.edu/home/baez/physics/Relativity/SR/acceler...
Can someone also confirm whether the following thinking is valid? The expansion of space means that the edge of the observable universe appears to be receding at the speed of light. As such, it has "N-1" dimensions and that is where the idea of a holographic boundary comes from? The same reasoning applies to the "N-1" dimensions of the event horizon in a black hole?
So if you're traveling at the speed of causality, everything you "hit" or go past happens instantly, because you're traveling "with" causality/information itself.
Since you could get to anywhere in the universe almost instantly by travelling sufficiently close to the speed of light, why do many science fiction writers and science fiction movies want to introduce faster than light travel? It doesn’t seem necessary; just tell the readers that the spaceship was travelling at 0.99999c to get to the other size of the galaxy in a week or at 0.99999999c to get there in a minute. (I didn’t do the calculation, but you can imagine what I mean.)
I’m going to guess that it’s easier to move the story along by saying “faster than light” than it is to explain the above. Most people would think the author made a goof by saying that something travelled 100,000 light years in less than 100,000 years if travelling at less than the speed of light. (Talking from the traveller’s perspective of course.)
The fact that you can describe this effect from the point of SR (by swuinting a bit) means that you can get GR time dilatation from SR time dilatation with no additional input.
The moment that we knew that the acceleration is the same as the gravity and that the speed of light in vacuum is constant we only had to think long and hard to see that gravity causes time to flow differently in different places.
But the universe is billions of light years across - if someone is travelling at just under the speed of light, wouldn't that mean it would take them billions of years (as experienced on the ship) to traverse the universe?
> why do many science fiction writers and science fiction movies want to introduce faster than light travel?
My thought on this, from a purely sci-fi perspective, is that accelerating close to light speed would use a phenomenonal amount of energy, and take a long time to do. Furthermore, time is experienced differently for those on the ship and those outside it. So with these points in mind, some kind of "hack" that allows you to fold spacetime and jump several lightyears instantaneously (as experienced by everyone) makes sense.
No, because time passes more slowly in the ship frame. This means it’s billions of years for your friends back home, but it could be hours for you.
Let's consider a ship, travelling from Earth, and say it somehow accelerates almost instantly to just below light speed, and travels for a distance of 1 light year. How much time would pass for those still on Earth, and for those on the ship?
Because this way you keep the human timescales for all characters. It allows you to tell stories more familiar to your audience while introducing elements that we wouldn’t be able to introduce without this plot device.
If you embark on a relativistic trip to Kepler-186f, when you return you will find a completely changed planet. The only way this would work is if every character spends most of the time at relativistic speeds reuniting from time to time as the whole universe ages around them.
That’s a nice premise, BTW.
Vernor Vinge does a great job in A Deepness In The Sky of creating a human space–fairing society that has to deal with some degree of relativity. Their ships only manage a 0.3× the speed of light, but they also use suspended animation to hibernate for most of their voyages. A trip where you age a year might mean that hundreds of years pass on the planet you’re going to. One character founded a vast trading coalition that was enormously successful in spite of this and other handicaps.
Greg Egan wrote a book called The Clockwork Rocket that is set in a universe where the space–time metric is different. This has huge effects on all aspects of physics from relativity to quantum mechanics, and he worked out all of those implications before writing the story. You can learn a lot about our universe just by contemplating all of the ways that this fictional Riemannian universe is different from our own Lorentzian universe. For example, in the Riemannian universe there is no fixed upper bound on speeds, light travels at different speeds based on its color, and thermodynamics is backwards so plants gain energy not by absorbing light but by emitting it.
As you approach the speed of light, (.9c, .99c, .999c...) two things happen.
1. Everything gets blue shifted. Light that would normally be coming at you in pretty shades of blue, green, and red become shades of ultra violet, then shades of x-rays, then shades of gamma rays.
2. More and more light arrives. As a result of length contraction/time dilation, you might get a century's worth of starlight in a second.
Depending on how fast you're going, the light coming in from in front of you might be extremely dangerous. Even a dim, cool Sun-like star might kill you with intense high energy gamma rays.
Left and right of you things would appear fairly normal.
Behind you, you'd have the opposite effect of what you see in front of you. Everything would be redshifted, and much lower intensity.
The one even faint possibility we know of, the Alcubier effect, puts you in a bubble of space time and warps that so it propagates at FTL speeds, but within that space time bubble you are stationary. You wouldn’t see anything outside the bubble though as it’s beyond an extreme distortion of space time that light cannot penetrate.
The Relativity prohibition is that anything with mass can not travel as fast as light because approaching c, mass increases requiring more and more energy while time slows, such traveling at c increases apparent mass to infinity, requires infinite energy, and time slows to a stop. The same thing could be said for anything moving FTL, as it approaches c, mass increases and time slows to zero. Relativity does not prohibit FTL travel, only travel at c.
Sure you can just define a line through space-time that is superluminal. That's basically equivalent to just defining a singular moment in time, the same way that an (inertial) trajectory defines a constant position.
Now if you were just wondering what you'd see if you simply changed position really quickly then you can just imagine putting lots of cameras in a long straight line and triggering them in turn to simulate a superluminal speed then you basically would just see the stars move more quickly than possible. You'd also see time progressing backwards on the stars that you are 'moving' away from and more quickly on the stars that you are 'approaching'.
So the stripy stars bit is not really that far off.
Or just watch Star Trek, as the iconic “moving through stars” happens throughout the series (mostly TOS, as others added different effects)
Given a finite collection of objects out to a certain radius (stars), relativistic length contraction will compress it along the direction of travel, so an observer looking out from the centre should see the density increase to a maximum when perpendicular to the contracted direction (in a way that's sort of the opposite of synchrotron radiation ending up tightly directed forward and backward). I guess the aberration described in your link will bend this fore-wards from the perpendicular, but it seems like it should still be visible.
The reason you don’t see an isotropic distribution of light from this uniform density is the distortion due to aberration + the synchrotron effect you mention (which makes the stars in the forward direction brighter).
So, in conclusion no “critical angle” but the dots of light appear more densely concentrated toward front and they are brighter, bluer.
You could kind of guess by trying to extend our models out to those speeds, but I think you're going to just find random guesses and formulas that no longer make any sense because you've exceeded the range of values they're defined over.
Looking backward or left/right, you will see nothing (darkness), because these photons have no chance to hit you. It will be more like a Pac-Man game: chose a photon, hit it, consume it, then move forward to a next photon.
Light from the rear red shifts (each photon has less energy), and there are fewer as some of the (formerly incident) photons "rotated" to the front.
(edit: typo)
(edit: didn't read the question closely, this is about approaching c, not exceeding it)