Is There A Cosmic Speed Limit? I Kirsty

Think you can travel as fast as you can – think again!

The idea that light always travels at the same speed, and that nothing can travel faster than that, is hard baked into modern physics. It is still difficult to get your head around the mind-boggling consequences of travelling in a spaceship with the beam of your headlights bouncing off in front of you into the vacuum of space. A stationary observer outside your ship would see those photons travelling at light speed – 299,792,458 metres per second. The things is, so would you, no matter how fast your ship was travelling in the same direction.

According to the laws of physics, as we approach light speed, we have to provide more and more energy to make an object move. In order to reach the speed of light, you'd need an infinite amount of energy, and that's impossible!

So, you’re on a fast train or in an airplane – did you ever notice the feeling of getting bigger throughout the trip? You may have heard that an object traveling at the speed of light gains infinite mass. But that's not exactly true. The object doesn’t actually gain physical mass, but it behaves like it has.

For example, if a 65kg person was travelling at 50% of the speed of light, they would behave like they had a mass of 87kg. At 90%, they would behave as if they weighed 172kg.

So, if mass can't travel at the speed of light, how come light can?

Light is made up of photons, which are massless particles and therefore they don't require energy to move.

Then if it doesn’t take any energy to move light particles – why can’t a photon travel faster than light speed?

This is because of something called time dilation. Time slows down as you approach the speed of light and when you reach it, time stops.

Photons don’t know what time is. For them everything happens instantaneously. Trying to make a photon go faster than the speed of light is like slowing down until you stop then trying to go even slower. It cannot be done. Its impossible!

Time dilation affects us all the time in everyday life, but its effects are so small we can't see it.

According to Einstein’s theory of relativity, “moving clocks run slow.” This isn’t him going crazy. This means that if you throw your clock off a cliff, it will show a slightly later time than a clock that wasn't thrown. This is true for all types of clocks – mechanical and biological. You actually age slower at higher speed. However, you would have to travel very fast to notice any difference.

Consider it like this – you are an astronaut on the international space station for 6 months. When you get back you would’ve aged 0.005 seconds slower than your friends back on earth. The International space station travels around the earth once every 90 minutes or so, but this is still only 0.003% of the speed of light.

If you, hypothetically travelled in a spaceship at 98% of the speed of light for just a few minutes, decades would have passed on earth for your friends – it’s like an effective but very expensive and dangerous anti-aging facial!

In ending does this answer the question if there is a cosmic speed limit. Well yes – and there is. The speed of light in a vacuum is the absolute cosmic speed limit. Nothing can go faster than 3.0 x 108 meters per second and this is due to a phenomenon that we experience in our everyday lives.

So, think you can travel as fast as you can. Well hypothetically you can travel up to the speed of light but only if you have an infinite amount of energy. Therefore if you do manage to travel that fast then you might want to let Einstein know, he may be a little jealous!