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If a person in a machine traveling faster than the speed of sound cannot hear the noise of a sonic boom, what might a person "see" or not see if they could (hypothetically) pass the "light speed" barrier? What would we, on the ground, see?
Question Date: 2002-04-15
Answer 1:

To be perfectly honest with you, I have no idea what things would look like if you could go past the speed of light. The laws of physics essentially break down for an object moving at the speed of light. You are basically asking the question, "If we throw out the laws of physics (so far as we understand it), what would the world be like?" I'm sorry for such an unsatisfying answer, but we can at least think about some of the basic issues related to this idea.

Breaking the sound barrier and breaking the light barrier are two entirely different scenarios. While there is no fundamental reason why traveling faster than the speed of sound would be impossible, there is one for breaking the light barrier. As objects approach the speed of light, the laws of physics (specifically Einstein's special theory of relativity) state that the mass of that object would also increase. As you get closer and closer to the speed of light, the mass continues to increase such that the mass would approach infinity (which would, in turn, require an infinite amount of energy to accelerate!) From the ground, if you could watch an object approach the speed of light, it would appear to slow down, or ultimately (from your point of view) come to a stop (as it came infinitely close to the speed of light) due to the time dilation. I should also note that there is nothing that says an object cannot be at a velocity greater than the speed of light, but that object would not be able to cross the light speed barrier, meaning it could not travel slower than the speed of light. Theoretical physicists have predicted such particles and named them tachyons. Does this mean that traveling faster than the speed of light is impossible? Perhaps not.

Einstein's special theory of relativity applies to "flat" space-time. However, Einstein's general theory of relativity permits speeds above the speed of light in a curved space-time. How can you imagine this?

As a crude example, imagine the Earth being a giant balloon (approximately spherical) with two people on it - one on the north pole, and one on the equator. Because it is so large, to each person it appears to be flat "locally" on the surface. But that "flat" frame of reference depends on what part of the Earth each one is at. Now imagine that the earth (balloon) expands. The special theory of relativity would say that each person would still find that nothing could break the light barrier. However, general relativity has no restrictions for the rate at which the Earth (balloon) can expand. Believe it or not, there are actually theoretical proposals out there that describe "warp drive" or "warp bubbles" based on this idea!

If you're interested in following up on that, try looking for information on "Alcubierre warp bubbles."

Answer 2:

As you approach the speed of light, you see the lengths of things in front of you shrink, and distances collapse. I imagine (don't know for sure!!!) that if you could BE a photon, traveling at light speed, you would lose all your individual identity and just become a wave, and then the concept of distance in front of you would be meaningless. Lengths would contract down to zero from your viewpoint, but you would cease to be an individual particle also... at least, that is my guess from what I know of Special Relativity.

I have no idea what you would see if you were traveling faster than light yourself... it is impossible, because you would have to have either infinite mass or zero mass. I have heard it speculated that you would see events running backwards in time.... I don't know if this is theoretically sound, though.

We do see particles that break the light speed barrier from the laboratory reference frame however. Not for particles traveling in a vacuum, though -only in a medium. They emit a bluish light - similar to what we hear when airplanes break the sound barrier. This happens ONLY for particles traveling in a medium like water or air, not in a vacuum, because nothing can go faster than light in a vacuum. HOWEVER, light SLOWS DOWN in water, which is why rulers look bent to you when you put one in a glass of water and observe it. Certain high-energy particles travel faster in water than light does IN WATER. When these particles are trapped in huge vats of water underground,they emit a bluish light which is called Cherenkov radiation, read more about this after the person who discovered it.

Answer 3:

As far as anyone knows, it is not possible to travel at the speed of light or to accelerate beyond it. Science doesn't/cannot answer any possible question, but only questions about the physically measurable world. As your question presupposes a state (a person traveling at the speed of light)which cannot be observed, your question is not answerable by the scientific method. Does this make your question a 'bad question'? I don't think so, many important questions cannot be answered by Science. Can you think of a few such questions?

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