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Have we tried in the past to run tests or do research to reach the speed of light ?

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Not on macroscopic scale. The Special Relativity theory is fairly well understood and says it's impossible for any objects that possess rest mass, period. The closer you get to speed of light the more energy you need to accelerate, additional energy gets increasingly converted towards mass instead of velocity, so to actually reach it you would need infinite energy and your spacecraft would become infinitely heavy.

The observed non-massless object that was closest to speed of light, known as "Oh-my-god particle", reached 99.99999999999999999999951% of speed of light; it was a proton, and it had 48 joules of energy - equivalent to a baseball travelling at about 26 m/s (94 km/h; 58 mph). Its mass was therefore about $5.28×10^{−16} kg$ - normally, a proton at rest weighs $1.673×10^{−27} kg$ so, due to all that energy, its mass was 315,000,000,000 times higher than at rest - and yet it didn't reach speed of light.

So, we are fairly sure that no, achieving speed of light normally is not possible.

There exists a theoretical solution, a kind of hack that would allow travel faster than light, without actually breaking Special Relativity - while the craft would travel below speed of light, specific curving of space-time around it would allow that chunk of space to travel relative to surrounding space at an extra speed. This is the concept behind Alcubierre Drive. And it's a very nice idea except nobody has any shade of a clue how to curve space like that. Especially that while we can stretch it by placing a massive object, there's no known way to do the reverse: compress it.

What IS being researched is spacecraft that would get somewhere into range of a couple percent of light speed. And we have a draft of something that can work and might be created within our lifetimes: Breakthrough Starshot. It would be based on minuscule probes a couple centimeters big, equipped with solar sails and propelled by mighty ground-based lasers, to about 20% of speed of light, towards Proxima Centauri.

This is still only a concept, and there are still many unresolved problems about it (e.g. we don't have any means of the probe to communicate its findings back, no way to fit a radio good enough on it.) But the propulsion part is fully realistic.

Accelerating humans near speed of light though? Not anytime soon. Maybe if we get nuclear fusion under control we could begin thinking of fusion-based rocket engines that could get somewhere into the ballpark. Otherwise we'll have to tame anti-matter, which might allow reaching somewhat relevant speeds - except as of now, it's not only impossibly expensive, we simply don't have any means to harness its power output into a form of propulsion.

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  • $\begingroup$ Can we get a source for that 142 grams proton anecdote? On Google, I've only found this ~142 gr proton plush which, by the way, is either a great reference or a huge coincidence! (fun, either way :) ) $\endgroup$ – xDaizu May 28 '18 at 16:05
  • $\begingroup$ @xDaizu: oops. I mis-quoted the article. $\endgroup$ – SF. May 28 '18 at 16:11
  • $\begingroup$ The linked article does not say that the OMG particle was a photon. Rather it is a "ultra-high-energy cosmic ray", but some observations were made comparing it with a companion photon. Still, great article. $\endgroup$ – user25936 May 28 '18 at 16:26
  • $\begingroup$ @jdv: Proton, not photon. The article doesn't say that either, took me a while to find what type of particle that was. It's an interesting subject because one of the theories of its origin is "exhaust of alien rocket engine of extreme specific impulse". $\endgroup$ – SF. May 28 '18 at 16:42
  • $\begingroup$ FTR, high-energy cosmic ray detectors actually rely on extrapolations from synchrotron results rather than direct measurement of the ray's properties, so it doesn't really make much sense to refer to them here. It is the particle accelerators themselves that give us so big confidence that relativity holds up to humongous energies. $\endgroup$ – leftaroundabout May 28 '18 at 17:07

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