Tachyons are hypothetical particles that all the time journey quicker than the velocity of sunshine. Einstein confirmed that such particles would enable for communication again in time, which opens up all types of issues with a basic rule of the universe. Whereas physicists have not proved that tachyons cannot exist, there’s good purpose to consider they do not.
The barrier that nothing with mass can journey on the speed of light is not simply an expression of the limitation of engineering or a illustration of a failure of creativeness. It is baked into the very legal guidelines of the universe, as expressed by Einstein’s theory of special relativity.
As an instance you wish to begin touring quicker than the velocity of sunshine. You begin from relaxation and provides your self somewhat nudge. As a result of you’ve mass, your nudge has to beat a little bit of inertia to get you going, however you ultimately get going. You mild up a rocket, for instance, and also you blast off.
Associated: Why is the speed of light the way it is?
However when you’re off the launchpad, you do not cease. You’ve some superadvanced engine that lets you preserve pushing, inflicting you to proceed accelerating. At speeds a lot decrease than the velocity of sunshine, every little thing is sensible: For each second you fireplace your engines, you get the identical quantity of acceleration and the identical increase in your velocity.
However as you method the velocity of sunshine, one thing humorous begins to occur. The identical quantity of vitality put into your engines begins providing you with much less and fewer acceleration, so that you get much less velocity bang in your buck. Regardless of working your engines to the acute, you end up inching nearer to the velocity of sunshine however by no means reaching it. Sooner or later, you understand that to realize mild velocity, you could put an infinite quantity of vitality into your engines — which you do not have.
The issue right here is that vitality is mass, as given by E = mc^2. The quicker you progress, the extra kinetic vitality you’ve, which implies you might be actually heavier the quicker you go. As you method the velocity of sunshine, your mass goes to infinity, so it takes an infinite quantity of rocket energy to make it to the velocity of sunshine.
The tachyon workaround
However these guidelines apply to things with mass beginning beneath the velocity of sunshine. Massless objects, like mild itself, robotically journey at mild velocity, by no means slowing down or dashing up. In 1967, constructing on work going again many years, physicist Gerald Feinberg proposed a brand new class of particle: objects with “imaginary mass.” (“Imaginary” right here refers back to the mathematical time period for the sq. root of -1.) These particles, which he referred to as tachyons, would by no means journey slower than the velocity of sunshine. In truth, they’d be pressured to all the time go above mild velocity and would have simply as a lot issue slowing right down to mild velocity as we do attempting to speed up to it.
Feinberg wasn’t the primary to think about faster-than-light particles, however he was the one to coin our phrase for them. Einstein toyed with the concept however discovered that such particles violated a central rule of the universe: causality.
Causality is so basic that it underlies every little thing we perceive in regards to the workings of the universe. Put merely, causality states that causes should come earlier than results. I’ve to textual content you earlier than your telephone beeps, I’ve to place a chunk of cheese in my mouth earlier than I can eat it, and so forth.
Inflicting bother
However tachyons are able to violating causality. To see how, let’s arrange somewhat thought experiment. I am sitting on Earth whilst you’re having some grand journey out within the universe. I wish to ship you a sign with tachyons, so I fireplace up my tachyon transmitter and beam off a message.
From my perspective, the tachyons race away from me at quicker than the velocity of sunshine in your course. Up to now, so good.
In case you’re standing completely nonetheless, then finally, the tachyon will attain you in much less time than it might take for mild to get there. You would not have the ability to see the tachyon coming till it already handed you, which continues to be no large deal. In case you had a telescope pointed at me, you’d obtain the tachyon earlier than seeing the picture of me urgent the button to ship it. Curious, however nonetheless no large drawback.
The problem comes when you begin shifting. In relativity, out of your perspective, you might be standing nonetheless whereas Earth seems to be receding. This introduces time dilation: Out of your perspective, every little thing within the universe — together with the motion of me urgent the button — slows down. In truth, when you’re touring quick sufficient, you may obtain my tachyon and ship a reply earlier than I even hit the button within the first place; you may ship a sign again in time.
When you enable for sending indicators again in time, you may play many enjoyable video games that create contradictions. You possibly can have a message despatched again to forestall your grandparents from assembly, which implies you’d by no means exist — however you could exist to return in time to forestall your grandparents from assembly. You possibly can set off an explosion that destroys the tachyon emitter earlier than it receives your message. You possibly can even destroy your self in your individual previous.
And since we do not dwell in a universe the place these contradictions and violations of causality occur, it appears unlikely that tachyons exist.
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