How Fast is Fast?

What is fast?

To know what fast is, we need to know what slow is.

A good example of slowness is a tortoise, a snail is slower, and a sloth is the slowest.

But that is only if we limit ourselves to the animal kingdom. Sea Anemone, an underwater plant-like creature (which can move on its own) travels at a speed of 0.0001 km/h. They typically do not move and when they do they creep very slowly using their pedal disk.

We can go even slower, Stars can keep fusing hydrogen for billions of years before they die out. But there’s one thing slower, xenon-124 is a radioactive isotope of xenon. Its half-life (time taken to decay) is an astounding 18 billion trillion years, which is even longer than the universe has existed up to now.

Now that we know what slow is, let's look at the other side of the spectrum.

You must have seen a motorcycle zoom past you and you could feel the air pushing onto you. That's pretty fast, isn’t it?

Going even faster

The fastest human-piloted plane flight was in a North American X-15 in the year 1967 where the plane reached its max speed going hypersonic at Mach 6.70 (around 7,200 km/h!).

The DARPA HTV-2 peaked at a max speed of Mach 20! (21,000 km/h). The Apollo spacecraft reached a speed of 39,897 km/h. The Voyager-1 space probe travels at a speed of 61,500 km/h, the Pioneer-10 is faster at 132,000 km/h, the Juno Space Probe at 265,500 km/h, and the Parker Solar Probe at 450,000 km/h!

Is 450,000 km/h even that fast?

If you were to travel at the speed of the Parker Solar Probe, you’d still take about 14 days to reach the sun! Yet light can reach us in 8 minutes! And if this probe were to pass by you, you wouldn’t even notice it, you would just simply explode from it simply passing by.

The speed of light is 1079252848.7999 km/h, now compare that to the speed of the Parker Solar probe 450000 km/h.

How fast can we really go then?

To see how fast we can go, we should know how fast we cannot go. To know what our limit is, we must understand that no object with mass can travel at the speed of light.

This is because mass increases with speed, but this phenomenon is only visible when near the speed of light. An object’s mass is only 0.5 times its regular at 10% the speed of light, but twice its normal when at 90% and it rises ever more when nearing the speed of light, and at the speed of light it reaches infinity.

Moving an object of infinite mass requires infinite energy, and there isn't enough energy in the universe to do that, thus only massless objects; photons which make up light can do it. This limit, however, only applies to objects, thus the universe itself expands at a ridiculous speed of 70km/s for every megaparsec covered (around 3.26mil lightyears).

What if we went the speed of light?

If you were even going half the speed of light, and a stationary object were to see you, you would look blue when you’re approaching and red when are going away. This phenomenon is called blueshifting and redshifting respectively, and it occurs due to compression and rarefaction of lightwaves around you.

But what you see would be completely different, your vision would be compressed into a circle of sorts, redshifted on the sides and blueshifted in the centre, this is because the world is approaching and departing from you at the same speed.

This circular vision gets smaller as you get closer to the speed of light. With the increase in speed of light, time also starts slowing down around you, this is a phenomenon of Einstein’s special relativity called time dilation.

What is time dilation?

When you’re on a moving train and you look out the window, you see objects closer to you moving faster and objects far away from you moving faster. Imagine you are looking at a clock tower and travelling away from it at the speed of light. The clock would stop ticking for you, but the clock itself hasn’t stopped moving and it continues ticking normally.

Einstein did this thought experiment in 1907, and he concluded, that the faster you move through space, the slower you move through time.

He imagined space and time as a single continuum like in the image beside, in which objects of mass create troughs. Now, the motion of an object through this continuum of space and time is a constant value, and so the faster you travel through space, to compensate, the time slows down, and vice versa.

This was the phenomenon Einstein discovered that changed modern physics.

Can we go faster?

Einstein set this universal limit for speed as the speed of light, but is that really our absolute limit? Although a fictional device (currently) warp drives can allow us to travel even faster than light itself. As dumb as it may sound in front of Einstein’s theory of relativity, scientists have given warp drives their shot and are researching them.

It doesn’t break any laws of physics as we aren’t actually travelling faster than the speed of light, but instead bending space-time in such a manner, it propels us forward even faster than light.

The warp drive requires many components that break our current understanding of physics and it will be a while before all these questions are answered, so we shouldn’t expect such technology to come in our lifetime, but it isn't wrong to work for it in the future.

Two recent papers – one by Alexey Bobrick and Gianni Martire and another by Erik Lentz – provide solutions that seem to bring warp drives closer to reality.

This is still a concept far from reality, and we might just never see them, but it is still fun and interesting to think about such possibilities. Like maybe travelling through a wormhole to the other side of the hole in spacetime. Maybe you could one day come up with something like this, so be creative and think outside the box and defy the limits given to you, just like the speed of light.

Article By:

Shantanu Shaji

(Writing Associate, TAO)

Design By:

Anushka Mishra

(Design Associate, TAO)