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Speed of light -

Light is fast, real fast. We’re talking about 186,282 miles per second fast (around 300,000 kilometers per second).

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Speed of light -

To put things into perspective, the fastest speed humans have traveled was aboard the Apollo 10 in orbit, at 24,816.1 miles per hour (around 39,937.7 km/h).

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Why is light so fast? -

Light is a massless particle and therefore can achieve such speed. For any mass to be moved at this speed it would require huge amounts of energy.

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It would require infinite energy -

Plus, mass increases as it accelerates towards the speed of light, so in theory, one would need an infinite source of energy to fuel the whole process.

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Infinite inertial mass -

And to make things even more difficult, there would be infinite inertial mass resisting the object. And this is why things can’t be faster than light...or can they?

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Vacuum -

Einstein’s theory of general relativity tells us that light travels faster than anything else…in a vacuum. So, what happens when light doesn't travel in a vacuum? Let's find out. 

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Water -

This is the case when light travels through water. Claudia de Rham, a theoretical physicist at Imperial College London, explains that "as light travels through a medium — for instance, glass or water droplets — the different frequencies or colors of light travel at different speeds."

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Water -

This is visible in rainbows, where we can observe the “long, faster red wavelengths at the top and the short, slower violet wavelengths at the bottom.”

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Water -

So, light actually slows down when it travels through water. This is an example of light not traveling through a vacuum, meaning its speed can indeed change. But can the opposite occur?

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Gamma-ray jet bursts -

Gamma-ray jet bursts are an example of something that is believed to travel faster than light.

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Gamma-ray jet bursts -

When stars collapse or collide, they create bright explosions. In fact, they create the brightest explosions in the Universe.

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Gamma-ray jet bursts -

The blasts responsible for gamma ray bursts were found to be able to travel through gas clouds faster than the speed of light. This is only possible because these Gamma-ray jet bursts exist in the dust clouds, not in the vacuum of space.

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Gamma-ray jet bursts -

An example would be the Big Bang itself. When it occurred, the empty space expanded faster than light.

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Quantum entanglement -

Quantum entanglement is like a bizarre long-distance relationship. It says that two subatomic particles can be linked together, despite being separated by light years.

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Quantum entanglement -

According to the theory, change induced in one particle will affect the other, no matter how far they are from each other. So, does this mean there is something traveling faster than light that connects them?

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Quantum entanglement -

This “spooky action at a distance,” as Einstein called it, is not an easy concept to grasp, but in a nutshell, the link seems to be a product of randomness, rather than the effect of something traveling faster than the speed of light.

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Wormholes -

Speed allows us to cross a determined distance in a specific time. For example, if you travel 100 miles at the speed of 100 miles per hour, it will take you one hour to travel that distance. Think of wormholes as shortcuts. In this case, you’d reach the destination faster than in one hour.

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Wormholes -

There’s a caveat though: no one has ever actually seen a wormhole in space. The science behind them does however exist (and some theories even propose they can be used for space-time travel).

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Wormholes -

Two black holes could potentially be linked together somewhere in space and create a large enough mass that curves space-time.

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Wormholes -

In simple terms, a mass can be pulled into one hole and come out on the other side (of the other black hole).

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Wormholes -

An apple-like shape is a good way to visualize wormholes. Mass would go in through the top and come out at the bottom. Can this shortcut be faster than the speed of light? Potentially. Though first we would need to have evidence that these indeed exist.

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Alcubierre Drive -

The Alcubierre Warp Drive is pretty much a speculation that a spacecraft can travel faster than the speed of light. All it needs is to travel in a vacuum. If the space in front of it is contracted and the space behind it is expanded, the spacecraft can travel like an isolated wrap bubble.

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Alcubierre Drive -

The theory is valid, mathematically speaking, but so far, NASA experiments with creating a wrap bubble were inconclusive.

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Krasnikov tubes -

The Krasnikov tubes theory is based on the Alcubierre Warp Drive. A Krasnikov tube is a mechanism that would allow a spacecraft to travel by creating a wrap behind it.

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Krasnikov tubes -

The wrap would propel it to its destination, and at the same time, it would create a “tube” where the spaceship would be able to travel back.

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Krasnikov tubes -

This tube unwinds time, so a journey that would take thousands of years could be done in just a few years through these superluminal tunnels. In theory, at least.

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Quantum tunnels -

Some particles can tunnel through barriers. The discovery was made in 1932, but it wasn’t until 1962 that semiconductor engineer Thomas Hartman published a paper about it.

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Quantum tunnels -

This was huge, and for years, scientists have been experimenting with it. After all, quantum tunneling seems to allow faster-than-light travel.

Sources: (Phys.org) (Livescience) (Sci News) (Space.com) (Scientific American)

See also: What physics says about time travel

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