What would happen if someone moved at twice the speed of light?

What would happen if someone moved at twice the speed of light?

To our knowledge, it is not possible for a person to move at twice the speed of light. In fact, it is not possible for any object with the type of mass that you or I need to move faster than the speed of light.

However, for some strange particles, traveling at twice the speed of light might be possible – and it could send those particles back in time.

A universal speed limit

One of our best physical theories today is the theory of relativity, developed by Albert Einstein. According to this theory, the speed of light functions as a universal speed limit on anything with mass.

Specifically, relativity tells us that nothing with mass can accelerate beyond the speed of light.

To accelerate an object with mass, we need to add energy. The faster we want the object to go, the more energy we will need.

The equations of relativity tell us that anything with mass – whatever its mass – would require an infinite amount of energy to be accelerated to the speed of light.

But all the sources of energy that we know are finite: they are limited in certain respects.

Indeed, it is plausible that the Universe contains only a finite amount of energy. This would mean that there is not enough energy in the Universe to accelerate something with mass up to the speed of light.

Since you and I have mass, don’t expect to be traveling at twice the speed of light anytime soon.


This universal speed limit applies to anything we might call “ordinary mass”.

There are, however, hypothetical particles called tachyons with a particular type of mass called “imaginary mass”.

There is no evidence that tachyons exist. But according to relativity, their possible existence cannot be ruled out.

If they exist, tachyons must always travel faster than the speed of light. Just as something with ordinary mass cannot be accelerated beyond the speed of light, tachyons cannot be slowed down below the speed of light.

Some physicists believe that if tachyons existed, they would constantly go back in time. This is why tachyons are associated with time travel in many science fiction books and movies.

There are ideas that we could one day harness tachyons to build a time machine. But for now, this remains a distant dream, as we don’t have the ability to detect potential tachyons.


It’s disappointing that you can’t travel faster than the speed of light. The closest star to us, other than the Sun, is 4.35 light years away. So, traveling at the speed of light, it would take more than four years to get there.

The most distant star we have ever detected is 28 billion light-years away. So you can pretty much forego mapping the entire universe.

That said, relativity allows for the existence of “wormholes”.

A wormhole is a shortcut between any two points in space. While a star may be 4.5 light years away in normal terms, it may only be a few hours away via a wormhole.

If there were real wormholes, they would allow us to travel great distances in a very short time, allowing us to reach the ends of the universe in a single lifetime.

Unfortunately, like tachyons, wormholes remain entirely hypothetical.

strange possibilities

Despite the fact that we can’t really travel faster than light, we can still try to imagine what it would be like to do so.

By thinking in this way, we engage in “counterfactual thinking”. We reflect on what things would be or could be if reality were different in some way.

There are many different possibilities we could consider, each with a different set of physical principles.

So we can’t say for sure what would happen if we could travel faster than light. At best, we can guess what could arrive. Would we start time travel, as some scientists think tachyons might?

I leave it to you and your imagination to come up with some ideas!The conversation

Sam Baron, Associate Professor, Australian Catholic University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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