What would it be like to go past the speed of light?

Question

Question #1:
I'm actually surprised that nobody has asked this question before, but theoretically speaking, what would it be like to go past the speed of light? This is actually only one of a few questions that I'll ask (below), but I'm just curious. What would it look like? Would you actually travel back in time, (I stand by the parallel universes theory), or would you just travel forward very quickly? Remember that I'm asking what would happen if you pass it, not if you reach it.
Question #2:
So suppose you had a very large, circular vacuum underground. Inside, you had a circular machine levitating through magnets. The magnets start making it spin, and it stretches out arms. Really far. Now I know about the law of conservation of angular momentum, but if you kept the center rotating at a constant speed while extending those long arms, would the tips eventually pass the speed of light? Because I think that you'd only need the same amount of energy to continue spinning the center at the same speed, but I may be wrong.
Question #3:
What would happen if you got to the speed of light exactly and stayed there. What would it be like? And would any of this affect the human body? If you got going at a gradual pace, would it do anything harmful to the human body, and would you be able to come out of light speed?
Question #4:
If it did take you back in time, would you be able to come out of light speed? What would happen if you went back before the machine was created? And finally, would you be able to send radio waves back in time? Like, to call someone who... died a long time ago?
I'm just curious, and thanks for reading through this whole question!

Answer 1

The basic answer to most of these is that, according to our current mathematics, going past the speed of light is nonsensical. Its no more meaningful than asking about the properties of a right angle that's only 89 degrees.

From a philosophical perspective, we have absolutely no concept of what it would mean for a massful observer to accelerate past the speed of light any more than you can ask how long it will take to count to infinity by 2's. We don't really have a meaningful theory for "what it would be like" to observe the world from any perspective except that of our own massful mortal coil. We can discus the mathematics of what a particle does, but not "what it would be like."

Indeed, we do have a conceptual particle called a tachyon which would travel faster than light. However, the theories which admit them are very narrow and do not discuss what it would "be like" beyond a mathematical model. I am not aware of any popular theories that do this; generally tachyons are frowned upon because they do suggest that there is anti-causality (causal behavior going backwards in time), and we currently do not observe any evidence that this occurs.

As for your magnetic idea, that one is less straight forward mathematically. The trick to that one is that you have to talk about the implementation of how you use magnets to keep that sphere rotating as you spin.

The key trick to this is that you have to oppose the centrifugal acceleration of the rotation. Particles on the tips of the device want to go in a straight line, and it takes a force to curve them and keep them on the circular path. We tend to ignore this at low rotational speeds, because the strength of the molecular bonds is more than sufficient. However, as you get faster and faster, it takes more and more force to keep the circular path, and it rips the bonds apart. This happens in the destruction of any physical spinning object, like a CD spun too fast.

Now you didn't say you wanted to use internal molecular bonds here, you said you wanted to use magnetic systems from outside. So how much force do these magnets need to produce? A lot. In fact, they have to produce an infinite amount of force, for the same reason that you can't accelerate to the speed of light. As you get closer to the speed of light, your mass increase due to the relatavistic effects of your increased velocity. At the speed of light, your mass would be infinite. Thus it would take an infinite amount of force to keep it on a circular path.

Even if you had magical infinite strength magnets, you still have to contain that force. The force from the magnets will push outward on whatever material is holding the magnets in place,a nd that will rip your device apart.

Now topics like this do come up when discussing relativistic effects on the event horizon of a black hole, but those are quite hard to follow because you end up with weird statements like "every spatial dimension points forward in time" which can be backed up mathematically but are awkward to work with in a "be like" sense.