I think it's just a natural question to ask, you know,
what's going to happen next, where does this all lead?
Where are we going? What's going to become of us?
And where do we stand in terms of the end of everything?
We think that the most likely way for the Universe to end
is something called the heat death, where the Universe is currently
expanding, it continues expanding and cooling and sort of winding down
and over trillions and trillions and trillions and trillions of years,
Everything kind of stops happening. The stars burn out and matter,
decays and black holes evaporate. Everything kind of fades to black.
It's just dark. Yeah, it's just dark. You know, it's rubbish.
Is the heat entropy? Is that like the second rule of thermo whatever?
Yeah. The second law of thermodynamics.
The second law of thermodynamics says that disorder only
increases into the future. So entropy disorder,
everything evolves more and more to be just waste heat.
That gets into some really interesting ideas about what is the
nature of time in that situation, because the arrow of time, the
direction into the future is sort of defined as where entropy increases.
And if entropy can't increase anymore, what does that mean about time?
Heat death, you're talking billions and billions of years, right?
Is there anything slightly more urgent that we should care a bit more more about?
The end of the Universe is not something that we should
consider as an imminent threat.
But there are scenarios for the end of the Universe that could
occur sooner than the heat death, so the Universe is currently expanding.
It's actually speeding up in its expansion, which is
something that's very weird, was only discovered in the late nineties.
Whatever's making it speed up, we call that dark energy.
We don't know what dark energy is and we don't know what dark energy
is going to do in the future. It could get more powerful.
If it did that, then the Universe could end somewhat sooner and
in a more dramatic way where it would actually rip galaxies apart,
you know, sort of tear the stars away from galaxies and
then planets away from stars and then and then explode
objects by just building up this expansion within
objects that would lead to what's called a big rip,
where the Universe is ultimately torn apart at some point in the future.
And it still would be a long way away. We're pretty sure it
could not happen within maybe two hundred billion years.
Okay, so we've already covered the heat death and the big rip.
I really like the sound of the big crunch.
The big crunch is what would happen if the expansion were to reverse.
And the moment we think that's probably not possible.
But because we don't know what dark energy is,
we also don't know for sure it's not something that could
change its nature and turn around and itself cause a re-collapse.
And so the immediate thing is galaxies would start to
get closer to each other, other galaxies would run into us.
That's not that unusual occurrence in the cosmos.
And in fact, we are gravitationally bound to our nearest neighbour
large galaxy, the Andromeda Galaxy, and we are fated to collide with
the Andromeda galaxy no matter what happens with the expansion.
So in about four billion years, we're going to slam into the
galaxy next door and it's going to rearrange the stars and orbits,
our two galaxies are going to get all messed up and there will be
a little bit more star formation and maybe the supermassive black
holes in the centres of our galaxies will spiral in and collide.
But it won't actually materially affect the solar system that much,
probably because individual stars tend not to collide during galaxy collisions.
There's just a lot of empty space. So colliding with the galaxy next
door is not the part that's scary about a big crunch, that can happen,
that's fine. The scary part is that as space is contracting,
not only is the matter getting closer together, but all of the
radiation in space is getting concentrated into a smaller region.
The light would be kind of compressed and get shifted toward ultraviolet x ray, gamma ray, hard radiation.
And that means that space would start to get hot. It would start to be full
of this hot plasma the way it was at the very beginning of the Universe.
It would start to cook planets, ignite the surfaces of stars.
You'd get thermonuclear explosions across the surfaces of stars
just from the ambient heat of space.
And then at that point, everything is pretty much over.
You've destroyed everything in the Universe,
I think this is the worst possible ending.
There's no escape. Right?
No, because it's space. You know, it's space. Where do you go.
What about some of the lesser-known candidate ways?
Heat death, big rip, big crunch. Those are all like, what is dark
energy going to do? How is it going to change the expansion?
There are two more that are more connected to what is the fundamental
physics that governs the Universe. So one of them is the kind of
blanket term for a few different possibilities that I call the bounce.
This is a cycling Universe, a Universe that goes from Big Bang
to end of Universe to new Big Bang. And there are several ways.
This can happen, and then the neat thing about a cycling universe is
the idea that something could kind of survive through the transition and,
you know, maybe a little bit of information could persist after
the end of the Universe. And some people find that sort of comforting.
My personal favourite of the Universe, though, is called vacuum decay.
And that one that one does not have any kind of silver lining.
It is a very complete ending. So the idea is that there's
certain rules that govern how physics works in our Universe.
You know, the fundamental constants of nature.
Those determine things like whether atoms can form,
whether protons and electrons attract each other.
If we have electromagnetic forces, all of that kind of stuff.
And those in turn are set by the Higgs field. Now, the Higgs field
is this kind of energy field that pervades all of space. And you
might have heard of it because it's connected with the Higgs boson, which
is this particle that's sort of an excitation of the Higgs field.
It tells us something about how particles got mass in the early Universe.
What happened with the Higgs field is has some kind of value to it. Right.
Like 10, 12, 12.5.
So, yeah, something like that. And we know that in the very early Universe,
less than a millisecond after whatever it started,
because it had a different value and all of physics was different.
You know, we had different forces. We had different particles.
Particles didn't have mass yet. And then the Higgs field changed.
And when it changed, it set up the conditions for our Universe today.
And now we can have atoms and molecules and chemistry and life and everything's great.
The problem is that based on our current understanding of the Higgs
field, we think that the Higgs field could shift again due to
a quantum tunneling transition, which is where you can have a
particle on one side of a barrier and it could suddenly appear on the
other side of the barrier without having to go round or through.
It's a very low probability event, but it happens all the time at
the subatomic scales. It's part of how we designed electronics.
We have microscopes that are built around the idea of quantum tunneling.
It turns out it can happen to the Higgs field, too.
And so what would happen is that somewhere in space,
anywhere in space, perhaps sort of right here, that the Higgs
field would undergo this tunneling event and find this other value.
And then when it does that, all the Higgs field around it would do the
same thing. And so it would create a little bubble of a different kind of
space where the laws of physics are different. It's called a true vacuum.
And that bubble would expand out at about the speed of light.
Universe being through our Universe?
When the physics inside and the physics on the outside collide, what happens?
So there will be a bubble wall around it, around this bubble that's high
energy. So the bubble wall hits you for a second, incinerate you.
Then once the bubble passes over you, then your atoms don't hold together
anymore because you don't have the same physics inside the bubble.
And then the other thing that happens is that the space inside the
bubble is gravitationally unstable. So you also then collapse into
a black hole so that you are very thoroughly destroyed.
We sure about this? Like the bubble comes through,
and it's really nice. And then all of a sudden we're really muscly and strong.
We are not sure about any of this. I've got like a flying horse.
Now this this is all, this is very cutting edge. We are not sure
about any of this, but this is where the equations currently...
I would be positive about the bubble of death.
I think maybe on the other side of the bubble is really cool.
A nice fresh start. Yeah. Exactly [laughs].
One final question for me. Is there anything to be hopeful for us?
I mean, it doesn't end well. You know, I mean, the Universe, [laughs]
the Universe is evolving and it's changing to be less
hospitable to life and order and structure and all of that.
The bright side is that we are at an amazing time in the Universe right now where we can observe it.
We can learn about the beginning of the Universe.
We can speculate about the end of the Universe.
We can understand how our cosmos works.
And, you know, we have a hundred billion years even before we lose the
ability to look at other galaxies. Right. That's a really long time.
So I think that we can be grateful for the time that we
have in the cosmos right now and understand that just because
it's going to end doesn't mean it's not worthwhile or good.
You know, there can be good things that don't last forever.