Why Space Travels Faster than Light
Up until the early 1990s, it was generally accepted that universal expansion was “a
thing”, but that it had to be slowing down. In theory, the fundamental force of gravity
should one day overcome the force of the expansion - grinding it to a halt. However, by the turn
of the millennium, new observations had shocked scientists by proving that expansion wasn’t
slowing down and was actually accelerating.
This is Unveiled, and today we’re answering the extraordinary question; How is it that
space travels faster than light?
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The speed of light in a vacuum isn’t just the fastest known speed that a particle can
reach, but it also acts as an effective speed limit for the rest of the universe. Lightspeed
comes out to almost 300,000 kilometres per second (299,792 exactly); which is the equivalent
of seven-and-a-half times around the entire Earth in a single second.
So, that’s the supposedly “unbreakable” speed, but next we need to consider Einstein’s
theory of general relativity. It says that if an object ever reached the speed of light,
it would then have infinite mass and a length of zero - which is, well, impossible. In 2012,
a team at CERN claimed to have measured neutrino particles travelling 0.002% faster than the
speed of light… but, it turned out that a loose fibreoptic cable had skewed the measurements.
More recently, and only marginally more successfully, a 2017 theory suggested that there might be
another particle, called a Tachyon, that really could travel faster than the speed of light…
only it’s a virtual particle existing in the quantum vacuum, so not all that practical
at the moment. And, regardless, we don’t actually require either of those theoretical
particles to answer whether anything travels faster than light because scientists now know
that something, one thing, already does… and that’s space itself.
Our universe is constantly expanding, and it’s for this reason that there are some
galaxies we will simply never be able to see. Some galaxies are so far away, and expanding
so quickly, that their light will never reach Earth. The crucial part, though, is that there
are even galaxies currently visible in our sky that will, in time, disappear from view
as they travel away from us faster than their light can keep up with. This process is best
imagined by picturing spacetime as though it’s a stretchy fabric overlaying the universe.
If it were fairly stretched on all sides, the most distant points would seem to stretch
more quickly. Say you were somehow stood in the centre, the things closest to you would
appear to move away at a slower rate.
According to updated calculations in 2016, the true speed at which the universe is expanding
is 73 kilometres per second per megaparsec - with a megaparsec equalling 3.26 million
light years. It’s heavy science but it essentially proves that distant galaxies are travelling
away from us at faster than the speed of light, with predictions claiming that the distances
between all objects in the universe will have doubled as a result in around 10 billion years
from now.
So, how can this even happen? Well, even though they appear to be, it isn’t technically
the galaxies that are reaching these speeds. Stay with us… It’s actually only the space
in between the galaxies that’s stretching faster than light. This phenomenon is often
explained as though the universe is a large piece of bread dough and galaxies are raisins
spread across it. As the dough expands when it’s cooked, the raisins become more and
more distant from each other - but the raisins themselves aren’t really changing at all.
Throw into the equation that the speed of light only truly applies to “local physics”,
or physical processes that occur relatively close to us, and the situation gets stranger
still. At the far ends of the universe, it’s thought that even our uppermost speed limits
could actually be broken - and that’s basically what’s happening with expansion. So, while
it’s true that we’ll never see a “local” spaceship flying faster than light, far off
stretches of space can (and are) hitting those speeds.
Interestingly, and as with many things in science, the initial confusion about universal
expansion (and whether space could or couldn’t exceed lightspeed) actually birthed whole
new avenues of study, as well. When the acceleration of the universe was first proposed it seemingly
defied logic… But the revelation has since led scientists and theorists to the idea of
dark energy.
What we now understand is that dark energy makes up 68% of our known universe. We know
this because that’s how much energy there needs to be in order for our universe to be
expanding as fast as it is. We now also know that dark matter, a similarly mysterious substance,
makes up 27% of the universe… which leaves everything else, all the particles and matter
in the visible universe, accounting for only about 5% of all there is. Dark energy and
matter were unknown to Einstein, but it’s effectively because of them that the speed
of light that was once thought to be unbreakable is actually being broken by space itself right
now.
As fascinating as it is, though, the expansion of the universe also points to a potentially
pretty lonely future. Should the universe continuing growing at a faster and faster
rate, then at some stage whole galaxies will eventually disappear from our skies. True,
they wouldn’t actually be “gone”, but we’d never be able to see them again; they
will have moved past the point at which the light they emit will ever reach Earth. In
this way, after many billions of years, the universe could effectively become invisible
to us - a blank expanse with far, far fewer stars and galaxies to contemplate.
All of which means that, thanks to universal expansion and the relative limits of lightspeed,
we (and any other advanced civilizations “out there”) are actually working under a deadline
of sorts to contact other living beings in the universe. Distant worlds may seem incredibly
far away as they are, but one day it could be physically impossible to even see them
through even the most advanced of telescopes. That deadline is aeons into the future, so
it’s not exactly a pressing concern right now… but if any kind of far future creature
ever wants to see the edge of the universe, then that’s the reality they’d be facing.
Time is ticking, and all because space travels faster than light.
What do you think? Is there anything we missed? Let us know in the comments, check out these
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