Have you ever wondered if it is possible to see the future? Humans throughout time have
certainly hoped so. But for most of us, that’s something in the realms of mystics
and fortune tellers. The idea that there might be some way to actually glimpse it is usually
considered the stuff of superstition. But that perspective might be wrong.
What if you were already seeing parts of the future, just in fragments? What if time could
be viewed with past, present and future at once? Before you worry, this is an Astrum video. I
originally intended this video to be the last one in my unified theory of everything series. But as
I was preparing the best way to demonstrate how strings could explain the principles of special
relativity, I took another, closer look. And I realised that there were some mind-bending
implications of relativity that contradict our perception of what really exists in the now, which
we had to tackle first. As it turns out, you might be seeing parts of the future already. And yes,
it’s time for me to explain with another diagram. I’m Alex McColgan, and you’re watching Astrum.
And to understand Everything, it’s time to scrutinise time, space and relativity.
We don’t tend to think of relativity in the way I’m about to show you, but it’s vital that we
improve our intuitive understanding of this topic, or no attempt to explain why special
relativity really happens will make sense. Besides, who doesn’t like having their mind
blown by cosmic weirdness from time to time? When it comes to special relativity, you might
have felt like you understood the gist of it. When an object travels at high enough speeds,
time slows down for it. At least, it does from the perspective of an outside observer
at rest. For the object itself, time seems to go the same speed, in a principle known as time
dilation - and curiously, if you travelled at light speed, from your perspective you’d be
ticking along as normal but everything else would suddenly be slowing down,
not you. It feels the universe shouldn’t work this way, with both sides thinking the other is moving
slower. But this does appear to be the fundamental rule of our universe - an object's rate of travel
through time seems to be down to the relative position of your perspective. There is no true
rate at which things travel through time. Weird already. But I wonder if you are
aware of just how far this principle goes. The implications get pretty mind-bending.
Let’s talk about a second element of special relativity; “Length Contraction”. This is a
bit of a weird one. From the point of view of an outside observer at rest, if an object were
to travel at a large enough percentage of the speed of light, the observer would start to
see the object flatten. A ball would become a giant pancake. This flattening occurs in the
direction of the object’s travel, and it has been shown to occur both mathematically, and
experimentally. We’ve fired protons in the Large Hadron Collider, and their collision patterns only
make sense if this pancaking is occurring. It’s very weird, but it does seem to be real – multiple
experiments seem to confirm length contraction, including the Kennedy–Thorndike experiment, and
experiments with Muon decay, where Muon particles falling through our atmosphere don’t decay as
fast as they should thanks to this effect. It’s worth noting, however, that just like
with time dilation, length contraction is a matter of perspective. If you were the thing that had
been accelerated to near the speed of light, you would not see yourself contract. Instead,
just like with time, you would start to see everything else contract, in the direction
of your acceleration. There’s some good maths that talks about why this is, but I won’t get
into that today, as it's the consequences of length contraction I want to talk about,
not so much its causes. After all, we want to get to the part where we start seeing the future.
And for that, we are going to need a thought experiment.
This thought experiment is known as the barn pole paradox, and it goes like this. What happens if
you try to fit a 40m pole inside a 20m barn? Let’s imagine the barn has a door on each side,
which you can slide the pole through. Now obviously, normally this task would be
difficult to do without bending or breaking the pole. However, if we take advantage of special
relativity, it is possible to do this. All you have to do is fire the pole into one open
door of the barn at near light-speed (let’s pretend for a moment that you can do that),
and hey presto! As long as it’s going fast enough, length contraction would occur, causing the length
of the pole to diminish to our necessary 20m. The pole would fit in the barn – for
a tiny fraction of a second, at least, before blasting out the other end. Mission success.
It would even be possible, if you could do it fast enough, for you to close and
then open both doors of the barn at once while the pole was still inside – proving
once and for all that the pole was inside the barn completely for that nanosecond.
But what happens from the pole’s perspective? Remember what I said earlier – objects travelling
at speed do not see length contraction occurring to them, but rather everything else existing in
the universe contracts in the direction of the object’s travel. So, we hit a problem here. The
pole would still see itself as a 40m pole, never a 20m one. Even worse, now length contraction is
happening to the barn, so the barn is even less than its original 20m length - now just 10m from
the perspective of the pole. So how does a 40m pole fit inside a 10m barn with both doors closed?
It sounds impossible. Surely this would result in broken poles or barn doors. But this is not
what the barn sees, so how can two different observers looking at the same event see two
completely different things happen? Have we entered a state of quantum superposition, where
the pole is both in and not in the barn? Are we about to split apart the universe into differing
multiverses? Is special relativity wrong? No. Our perception of reality is wrong.
There is an answer to this. But you’re not going to like it.
Watch closely. According to relativity, this is what would happen, from the pole’s point
of view. The pole enters the barn just like we would expect, and then… There.
Did you see it? Perhaps, but what did you just see?
You just saw an example of the myth of simultaneity. And remember, this is really
what happens, according to special relativity. Events that are simultaneous from one point of
view are not simultaneous from another. To be clear, this is not just a weird consequence of
light taking its time to reach us. If we were just dealing with an optical illusion caused
by light taking its time to move to our eyes, then we’d see the closer event happen first,
and the more distant event happen second. But this is happening the opposite way around – in
this case, and from the point of view of the pole, the more distant event spacially happens first,
and the closer event happens second. In other words, this is not just a trick of the light,
but the suggestion that something more fundamental is going on.
What is going on? When I first learned this,
it boggled my mind. It seemed wrong as a matter of principle. But the more I thought about it,
the more it started to make sense, based on my understanding of the universe – and
the more startling implications started to arise. Don’t worry, I’ve not forgotten about
that “seeing the future” thing. I’ll get to it. Let’s take another look at what’s happening here,
but this time let’s bring in a little colour coding, and our old friend, a 4D space-time
diagram. Hopefully you are familiar with these already, as I’ve done a few videos that have
included them. If not, here’s a great video we did on the subject, which you should give
a look. To recap, though, just imagine that all of space has been flattened down to the
1 line along the bottom of our graph, while an object’s motion in time is tracked along the side
of the graph. Here is the barn’s timeline, according to its motion in space and time:
From the point of view of the barn, it is not moving in space, so we draw the
arrow directly up – it is only moving into the future. I’ve painted the shutting and opening
of the two doors as two different colours here on the graph. Note that they are separated by space,
but they occur at the same moment in time, at least from the barn’s perspective.
Now, for our first complete perspective of this event, let’s add the path of our pole.
As our pole starts moving, length contraction occurs,
and the pole drops down to 20m. Eventually it arrives at the barn, and our two events
occur – both barn doors shut at the same time, and the pole is snuggly inside. All good so far,
from the barn’s point of view. But what does the pole see?
Let’s make our pole the stationary object in this diagram. After all, this is relativity,
and from the pole’s perspective it is the barn that is moving quickly towards it,
not the other way round. This makes it easier to assign length contraction to the barn, which
is what relativity says we should be getting. We cannot simply add the barn to this diagram
as an object that’s parallel in orientation to the pole. It just wouldn’t work. The barn,
now narrower, would intersect with the pole with both doors closing and opening at the
same time, so the pole wouldn’t fit. But what if we pivot our barn slightly,
from this to this? Essentially, this isn’t too unreasonable, as we’ve just turned the
first diagram slightly on its side. Now, the sequence works. With this,
the part of the barn furthest from the pole meets it first, and the pole sees the orange door shut
and open. Then, as time goes on and the pole and the barn proceed further into the future,
the pole’s other end reaches the blue door, which also shuts, then opens.
Thanks to this vector in time and space, it’s possible for the barn to not hit either end of the
pole with its shutting doors. The order of events is right – from the pole’s point of view, the
barn’s further orange, “back” door shuts and opens before the barn’s blue “front” door does. This is
what special relativity tells us should occur. But do you see why this configuration is so
strange? It implies to me that the barn itself is not simultaneous,
while it is in motion. Here’s where we’re jumping from the paradox, into my own thoughts about it.
What do I mean by simultaneous? I mean that we expect the barn to exist as a discrete entity,
at a single point in time. It does exist, with every part of it happening in the same “now”, even
if it’s undergoing a little time dilation here and there. But the barn the pole sees is not happening
in a single now. Part of it is ahead in time, and part of it is lagging behind. And you can see
both parts at once. The barn is not simultaneous because you can see it across a range of times.
Its length might be contracting, but the dimensional space you see
it occupy in time seems to you to be growing. We do not think like this. But the idea has a
beautiful sensibleness to it, in a universe of 4D space. Like when a racing car swerving
to the left causes its right wheel to protrude further forward, when you move to the left on
our spacetime diagram, it causes the part of you furthest away from the direction of motion to
protrude into the future more than the part that’s closer. That’s just geometry. For the record,
this seems to happen as a gradient, along the whole of the object in motion.
This way of thinking also allows length contraction to conceptually make a lot more
sense. After all, if our pole is in motion, and the front of the pole is further in the
past and the back of the pole is further in the future, then it makes sense to consider
where each part of the pole exists in space during those moments in time. The front of the
pole that exists further back in time has not travelled as far as the rest of the pole. So,
the start of the pole is further back. Similarly, the back of the pole which exists further forward
in time has by then moved further through space compared to the rest of the pole. So the back
of the pole is further forward. What happens when you combine a dawdling front with a further ahead
back? Length contraction. The only surprise is that it seems that we can see this, in
experiments in the LHC and other places. Somehow, we are seeing across a cross-section of time.
So, it works. It just feels like it shouldn’t. You might think this is a little out there…
but consider. What would an object that didn’t exist all in the same moment in time look like,
to you? Could you tell it apart from any other object? Well,
it would probably look mostly the same… right up until some part of it changed what it was doing,
and you watched as the rest of it caught up. Which is what we see here. So it’s not
unreasonable to think of it this way, and it certainly helps our intuition.
This is the state of affairs for objects that are moving. Or, if we are moving,
that’s the way we see everything else. Which has some pretty mind-bending implications about what
we are seeing right now across the universe. Of course, this only applies when things are
moving at a substantial portion of the speed of light. So in the day to day,
you probably wouldn’t notice it. And because of the great speeds involved, it’s difficult to
imagine a scenario where you could take advantage of this principle, even if you could use the first
barn door closing to predict the future of the second. There are limits on how fast information
can travel, after all – and this time-stretching is only noticeable when objects are travelling
near to that limit. And while I’ve talked about the future of the barn and the past of the barn,
perhaps that’s the wrong point of view. To you, these events are all in the now. Your
now. It’s just the barn that might see things differently, with its own now where it's closing
and opening its doors simultaneously, and you are the one who’s splayed out as a range across time.
But it just causes me to think about the universe in a very different light.
Space and time really are just a matter of perspective, because there is no one true now.
There’s just your own personal path, and the paths other objects take in 4D space. And just because
I see time as being one thing in my reference frame, doesn’t mean it works that way for you in
yours. In yours, time might just be more space. So, when I finally release part 4 of my unified
theory of everything, that is the strange universe that I will be trying to explain.
One where time and space really are relative points of view. Wish me luck.
Time and Space might be all relative depending on your point of view, but there are some things in
life you certainly hope aren’t so subjective. For instance, if you go online and purchase a
new laptop or snazzy jacket, the last thing you want to hear is the website say “Sorry, we never
received your money,” when from your point of view you definitely finalised the transaction. Sadly,
this is what some scammers do; mimicking real retailers, they get you to input your card
details, so they can collect your money then vanish into thin air - all without you getting
that new 40m pole for your 20m barn. Nord VPN, the sponsor of today’s video, can help you see
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Meanwhile click the lin to this playlist for more Astrum content. I’ll see you next time.