The Conversation contributed the article to Space.com's expert voices.

Sam Baron is an associate professor at the Australian catholic University.

If someone moves twice the speed of light, what would happen?

It isn't possible for a person to move at twice the speed of light. It's not possible for an object of mass to move at the same rate of light.

It is possible for certain particles to travel at twice the speed of light.

If the speed of light was less, what would happen?

## A universal speed limit

The theory of relativity was developed by Albert Einstein. The theory says that the speed of light is a universal speed limit.

Einstein told us that mass can't accelerate past light's speed.

Adding energy is needed to accelerate an object. The more energy we need, the quicker the object goes.

Everything with mass would need an infinite amount of energy to be accelerated to the speed of light.

All of the sources of energy are limited in some way.

It is possible that the universe only has a finite amount of energy. There isn't enough energy in the universe to speed something up with mass.

We have mass, so don't expect us to travel at twice the speed of light.

## Tachyons

Anything with ordinary mass is covered by this speed limit.

There are particles with a special kind of mass called animaginary mass.

There is no proof of tachyons. It can't be ruled out that they exist.

Tachyons travel faster than light if they exist. Tachyons can't be slowed down to below the speed of light because they can't be accelerated past the speed of light.

Physicists think that tachyons would travel backwards in time if they existed. Tachyons are associated with time travel in science fiction.

There are ideas that could be used to build a time machine. We don't have the ability to detect tachyons so this is a distant dream.

## Shortcuts?

We can't travel quicker than light. The sun is the closest star to us. It will take more than four years to get there.

The farthest star we've found is 28 billion light years away. You can't really keep up with the whole universe.

Einstein's theory of relativity allows for the existence of wormholes.

A wormhole is a way to get between points. A star may be 4.5 light years away in normal terms, but it may only be a few hours away through a wormhole.

It would be possible for us to travel to the farthest reaches of the universe in a single lifetime if there were actual wormholes.

Like tachyons, wormholes aren't real.

## Strange possibilities

We can still imagine what it would be like to travel faster than light even though we can't.

We are engaged in counterfactual thinking by thinking in this way. We are thinking about what would happen if reality was different.

There are many possibilities with different physical principles.

We don't know what will happen if we could travel faster than light. We don't know what will happen. Scientists think tachyons could travel back in time.

It's up to you and your imagination to come up with some ideas.