Why is it theoretically impossible to break the speed of light?

Question

I was pondering relativity (as you do) and wondered why a particle can't go faster than the speed of light when we could could send a particle at the speed of light in one direction, and another particle in the opposite direction so that relative to each other the first could be considered still and the other is therefore travelling at the speed of light *2. Extrapolating that idea, why not send a particle accellerator at the speed of light in one direction, and then accellerate a particle from it so the particle is going at the speed of light *2, and then from our lab (where we started) do the same thing in the opposite direction, therefore creating particles travelling at 4* the speed of light.

Clearly some pretty major technological issue to overcome :) but surely that sound in theory???

Answer 1

Theoretically as an object approaches the speed of light it adds mass rather than speed (from E=MC2), so an object would become more massive rather than faster. Some theories say that you would need to use all the Energy (and matter) in the Universe to achieve the speed of light. It's not just the speed of light, but anything that's more than a minute fraction of it gets hit by this.

But it's all just theory. We just haven't been able to debunk it.

Answer 2

In your example, you sure can send two particles in opposite directions at nearly c relative to an observer on the ground. And the observer will observe that the distance between them increases by 2c. That's not what we mean by "breaking the speed of light" though. Each particle in that experiment travels at less than c. If you were an elf sitting on one of those particles, then when you looked at the other one, you would observe it traveling at less than c, not at 2c.

No observer anywhere will ever observe any particle traveling at greater than c.

Answer 3

Mass of the object approaches infinity as the velocity approaches the speed of light.

Another part of the theory of relativity states that even sending particles at the speed of light in opposite directions, from the point of view of either particle the difference in velocity is still only the speed of light.

That gets you into the part of the theory where time is not constant....

Answer 4

Just a note about the first part as to why when one object is moving at the speed of light, and there is another object moving at the speed of light in the opposite direction. You have made an assumption in your calculation, you have assumed that velocities add linearly. Why would you assume this assumption is valid for all speed? Simply, one can do a test and prove your assumption wrong within the scientific method.

Answer 5

Tachyons move so fast they go backwards in time...
-->Tachyons are HYPOTHETICAL faster-than-light particles. Physicists asked themselves, "What would be the characteristics of matter if it did move faster than light?" (a kind of thought experiment.) One odd thing is that to slow down a tachyon, you would have to put energy into it. In fact, it would take infinite energy to get it to slow down to the speed of light that is if it has any mass. That brings me to the next interesting point - one way to view the momentum of tachyons is to consider that they have imaginary mass. So far any attempt to observe a tachyon has come up dry, and most physicists have abandoned the idea that tachyons might be real. The only tempting recent clue was a recent measure of the rest mass of a neutrino. They got an imaginary number. This result was NOT attributed to tachyon properties, in fact, the experimental report attributed the results to possible errors in some of the supporting information used to make the calculations.

Answer 6

i can see what you are trying to say in your thought experiment but you need to remember that light always travels at c. it leaves the source at speed c and reaches the observer at speed c, regardless of their relative velocity. its for this reason that we see phenomena such as time dilation.

Answer 7

Tachyons are possible in a universe where only tachyons exist. That means there are no tachyons in our universe.

Answer 8

The mass increases to infinity, and this would require more energy than there is in the universe.

Answer 9

take this equation T1= T0
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sqrt(1-v^2/c^2) (time dilation)
if v=c then c^2/c^2 = 1
1-1=0
sqrt(0) = i
thus not possible