Thanks to Squarespace for sponsoring today’s
video. How would your universe change if you approached
the speed of light? What would everything around you look like? How would space and time act? The answer is: a lot different from what you
are currently used to! To travel the speed of light isn’t actually
possible for anything other than massless particles, like photons. It would require infinite energy to get something
with mass to that speed. The energy required exponentially goes up
the closer you get. But there are instances of matter coming close,
we’ve observed some particles travelling 99% of the speed of light. Now for you and me, we have no hope of ever
approaching these speeds, but if you did manage it, what happens to space and time from your
perspective would be very noticeable. Let’s ease you into this, as it’s going
to be a bit tricky to wrap your head around. We will simulate going from standing to travelling
almost the speed of light. This is a fun little game called ‘A Slower
Speed of Light’, released by MIT, demonstrating what would happen if the speed of light got
progressively slower, eventually to walking speed. At first, my character looks around and sees
the world normally. But as I start to pick up these orbs, instead
of speeding me up, the game slows the speed of light down, to simulate what it would look
like if we were travelling extremely fast over vast distances. As the speed of light slows, what becomes
apparent to you? The first thing I notice is that colours start
to change. This is because of something called the Relativistic
Doppler Effect. You see, when you look around and you see
colour on objects, this is because light is reaching your eyes at specific wavelengths. The longest wavelengths you can see are reds,
and shortest wavelengths are violets. Beyond the range of our sight are infrared
and ultraviolet. But when you start going very fast, because
of the doppler effect, some of the wavelengths that were in the infrared and ultraviolet
now shift to wavelengths you can detect. Suddenly, things that were invisible to us
before, become visible, like heat in infrared and florescent substances in ultraviolet. The faster you travel, the larger your visible
range now becomes. Light does travel in waves, but it is also
a stream of particles, called photons. As you head into the flow of particles at
speed, more particles will hit your eyes, making everything ahead of you brighter. On the other hand, if you look behind you
as you travel forwards, everything will get darker, because less photons are reaching
you. This is known as the Searchlight Effect. What else do you start to notice? You may notice that we seem to be gradually
speeding up. But actually, our speed always stays the same
throughout this game, we are just walking like we were at the beginning. This is a result of Special Relativity, namely
Time Dilation. One of the laws of the universe is that the
speed of light is a constant. However, space and time are not, and can be
warped. So, when you start moving, two things change:
your time and your distances relative to stationary observers. Let me explain. Time goes slower for an object that goes faster. This has been proven. If you have two clocks, one stationary, and
the other in rapid motion, on say a rocket, eventually the times on each will go out of
sync. This is why the times on satellites in orbit
around Earth need to be occasionally adjusted, or they’d go out of sync with Earth based
clocks. Not by much, a few milliseconds per year,
but it would add up eventually. The faster you go, the more time dilation
happens, until should you hit the speed of light, the rate of time reaches zero. This means photons, or light particles travelling
the speed of light, are unaffected by the passage of time. But let’s go back to how time dilation affects
us in the game. Removing the lighting effects will help us
see this more clearly. Now remember, throughout the game, our walking
speed stays the same, it’s the speed of light that slows down as we collect more orbs. And yet, it seems that we move a lot faster
towards the end of the game than at the beginning. What is happening here is that our time is
going slower than everything around us. As a result, it’s like the distances of
space are shorter, meaning we get somewhere quicker from our perspective. In practice, this means that if we travelled
in a vehicle that approaches the speed of light, and we travel for one year at that
speed, it all seems normal for us, but 10 years have passed for people on Earth. Should you actually be able to travel the
speed of light, you could get anywhere in the universe instantaneously from your perspective,
but on Earth, however far in light years your journey takes you will equal the equivalent
amount of years from their perspective. Do you want to go 40 light years away and
can travel the speed of light? You get there instantaneously from your perspective,
but for people on Earth, you show up there 40 years later. Again though, in practice light speed travel
is impossible for anything made of matter. The last effect is a weird one, it’s like
our field of view changes. This is from the effects of the Aberration
Of light and Lorentz Transformation. Light takes time to reach our eyes, and when
we see anything, we are seeing that object in the past. Even now, you are watching this video with
a tiny tiny tiny time delay, as light takes time to leave your screen and reach your eyes. As we move in the game, that object we are
seeing isn’t where we think it is anymore. You may have thought as you’ve been watching
this video that I must be useless at computer games because I keep crashing into walls and
missing the orbs, but this effect means that I’m not standing where I think I am, because
the more orbs I have, the slower light is travelling, so I actually need to start turning
a little ahead of what I’m used to, which is difficult to comprehend while navigating. It’s like playing with a lag. This effect also means that I can see much
more of my surroundings in one go, this animation helps show why. The light source is moving relative to me
as I move forward, but because the beam of light takes time to reach me, I see it where
it was relative to me in the past. When there is a lot to see all around me,
it’s as if my field of view increases the faster I travel, as I’m suddenly seeing
all these objects as they were relative to me in the past. Light, space and time get more complicated
still, but I won’t delve into it in this episode. All I can say is that I’m glad light appears
almost instantaneous for us. This game was a bit of a thought experiment
to see what the world would be like if light was slow, but it hasn’t even gone into the
other really problematic scenarios like Earth travelling around the Sun at the speed it
does, how all our electronics would be affected, and other major issues. In the opposite vein, us being able to approach
the speed of light would be beneficial for travelling large distances in short times,
however time is passing normally for people on Earth, meaning travelling anywhere in the
universe and coming back again could be possible for you, but Earth would look a lot different
on your return, with years, decades, millennia or more having passed depending on how far
you went. On your journey, due to the various effects,
outside your ship everything would look warped, your field of view would be greater, a greater
range of light wavelengths become visible, and in front of you would be much, much brighter. So, there we have it, how your universe would
change if you approached the speed of light. Thanks again to Squarespace for sponsoring
this video. Squarespace gives people a powerful and beautiful
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podcasts or music, with ITunes support. Or something I find particularly useful, which
is the ability to link various social media platforms to your website and embed videos! So, if you’re looking to build a website,
give it a go! If you use the link squarespace.com/astrum
you can try it out for free and get 10% off your first purchase. Thanks for watching! Did you like this video? Check out this playlist for more Astrum Answers! Do you want to help pick the next question
that gets answered? Become a Patron or a member and take part
in the fortnightly polls! Links are all in the description. All the best and see you next time.
