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Space & Astronomy

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

May 24, 2022 · Comment icon 24 comments

Image Credit: CC BY 2.0 BarricadeCaptures / Flickr
Einstein's theory of relativity would seem to preclude the possibility, but what if it could be done ?
As far as we know, it's not possible for a person to move at twice the speed of light. In fact, it's not possible for any object with the kind of mass you or I have to move faster than the speed of light.

However, for certain strange particles, travelling at twice the speed of light might be possible - and it might send those particles back in time.

A universal speed limit

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

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

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

The equations of relativity tell us that anything with mass - regardless of how much mass it has - would require an infinite amount of energy to be accelerated to the speed of light.

But all of the sources of energy we know of are finite: they are limited in some respect.

Indeed, it's plausible the Universe only contains a finite amount of energy. That would mean there isn't 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 travelling at twice the speed of light anytime soon.


This universal speed limit applies to anything with what we might call "ordinary mass".

There are, however, hypothetical particles called tachyons with a special kind of mass called "imaginary mass".

There is no evidence tachyons exist. But according to relativity, their possible existence can't be ruled out.

If they do exist, tachyons must always be travelling faster than the speed of light. Just as something with ordinary mass can't be accelerated past the speed of light, tachyons can't be slowed down to below the speed of light.

Some physicists believe that if tachyons exist, they would constantly be travelling backwards in time. This is why tachyons are associated with time travel in many science fiction books and movies.
There are ideas that we might someday 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 we can't travel faster than the speed of light. The nearest star to us, other than the Sun, is 4.35 light years away. So, travelling at the speed of light, it would take more than four years to get there.

The farthest star we've ever detected is 28 billion light years away. So you can pretty much give up on charting the entire Universe.

That said, relativity does allow for the existence of "wormholes".

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

If there are any actual wormholes, they would let us travel great distances in a very short period of time - allowing us to get to the farthest reaches of the universe within a single lifetime.

Unfortunately, like tachyons, wormholes remain entirely hypothetical.

Strange possibilities

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

By thinking in this way, we are engaging in "counterfactual thinking". We are considering what things would, or might, be like if reality was 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 with any certainty what would happen if we were able to travel faster than light. At best, we can guess what might happen. Would we start to travel back in time, as some scientists think tachyons might do?

Sam Baron, Associate professor, Australian Catholic University

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

Read the original article.

Source: The Conversation | Comments (24)

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Recent comments on this story
Comment icon #15 Posted by qxcontinuum 2 years ago
And yet the light we powered and produce with two batteries, can travel at light speed. 
Comment icon #16 Posted by Emma_Acid 2 years ago
Did you not even read the first paragraph of the article?
Comment icon #17 Posted by Hyperionxvii 2 years ago
Did you even read the title of the article? 'What would happen if you moved at twice the speed of light ?' YOU is not a strange particle. At least most people are not.   
Comment icon #18 Posted by SHaYap 2 years ago
~ ~  
Comment icon #19 Posted by badeskov 2 years ago
So who wrote this article again? That is simply not true. For obvious reasons we have not detected anything that far away.  Cheers, Badeskov
Comment icon #20 Posted by XenoFish 2 years ago
Since it can't be done it is a pointless and meaningless question.
Comment icon #21 Posted by Cookie Monster 2 years ago
E=MC2 Well, the M can be removed, the Higgs Field is confirmed to exist. It means mass is not an intrinsic property of matter, but matter gets it from interacting with the Higgs Field. Currently two proposed methods to decouple matter from the Higgs Field exist. One cannot be done, it involves heating space to astronomical temperatures last seen shortly after the Big Bang. The other would be an intensive light field around the spacecraft. 
Comment icon #22 Posted by badeskov 2 years ago
Uhm, I’m not sure where you get that from. Mass is indeed an intrinsic property of of matter, but now we have evidence that the Higgs boson and associated field facilitates that mass.  So far those methods are highly speculative and does not invalidate the theory that mass is an intricate property of matter.    Cheers, Badeskov
Comment icon #23 Posted by ExoPaul 2 years ago
My theory (based on no science) Time travel is probably possible, but not while we have mass. Know what doesn't have mass? A soul. When we die, we shed our physical bodies that contain the mass, and our spirit moves on, which according to mediums display the ability to move back and forth through time and are simply an energy, not a physical construct.
Comment icon #24 Posted by Portre 2 years ago
Those reasons are not obvious to me.  The observable universe is a sphere extending 46.5 billion light years due to the universe expanding for 13.8 billion years

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