otherwise, you know another episode in a while.
Dark energy is part of the fabric of space itself, and it turns out that when it's created
by the universe, there's an offset in how the universe is shaped and how the universe
is expanding.
So unfortunately, you don't get anything for free, and so it's pretty much impossible
to undo, at least as humanity, the effects of dark energy, and it's effectively impossible
to harvest it in any way, shape, or form.
So because dark energy is part of the fabric of space, as the universe speeds up over time,
more space is made.
More atoms and more dark matter are not made, and that means that the fraction of the universe
is going to change over time.
Right now, 73% dark energy, but if we wait another 10 or 15 billion years, then 95% of
the universe will be dark energy because the universe has expanded so much.
And so yes, the balance of the universe changes over time because atoms and dark matter get
diluted by the expansion of space, and dark energy doesn't.
Gravity is not completely understood.
What we know is that anything that has mass or energy has gravity, and we suspect there's
some particle which is thrown around between objects which causes the force.
And so really, gravity is stored in everything there is, but unfortunately, the theory of
how gravity fits in with quantum field theory, which is the other three forces of nature,
that is a big outstanding problem for physics that has yet to be resolved.
So Neptune is a planet much bigger than the Earth, and it's made out of gas.
And its year is a little bit longer than 160 years for it to go around the Earth, so that's
like a year.
But it rotates very quickly, 16 hours and 6 minutes it takes to turn on its axis.
So its day is about 16 hours and 6 minutes on like the 24 hour day that we have here
on Earth.
The end of the universe is something that if the universe were eventually to collapse
on to itself and have the opposite of the Big Bang, that Ganabgib I talked about, then
that would be the end of the universe, but the end of the universe would be in time rather
than some place.
And so it appears that's not what the universe is doing, and so really there is no end of
the universe.
There's no place in the universe that you could go that has an edge, and since time
goes on forever, it's without end that direction as well, it appears.
In the very, very distant future, we'll say hundreds of trillions of years in the future,
it turns out that every star in our galaxy will have burned its fuel and will have died.
And so there will be literally no heat left in the universe.
Every part of the universe will be cooling down to absolute zero, and that will make
it impossible for life to exist into the distant future.
Instead, the universe will just sort of fizzle out.
And so it's a very bleak end for the universe.
So as the sun ages, its nuclear furnace, which is converting hydrogen into helium, is actually
heating up, and so the sun is getting hotter and hotter over time.
And so the Earth, turns out, has been compensating for this by absorbing more and more carbon
dioxide.
And so we've been sort of used, the Earth used global warming to keep itself warm early
on, and that carbon dioxide is slowly getting incorporated in rocks and things over time.
So as the Earth gets hotter, probably about 800 million years from now, the Earth will
be extraordinarily hot because almost all the CO2, despite what humans are doing now,
will be out of the atmosphere.
In terms of the sun coming towards us, no, it turns out that the Earth is just minutely
moving away from the sun, but it's almost imperceptible.
And that's caused by tidal forces.
The sun affects the tides on the Earth, moves the oceans around, and those things end up
taking and dragging energy out of the Earth's orbit.
So over time, we go a little bit further away from the sun.
That being said, as the sun heats up, it gets a little bigger, and so in some sense, the
surface gets a little closer to us.
So when we measured the fact that the universe was accelerating, that was a measurement that
we made using these exploding stars, supernovae.
But the theory behind why the universe might be accelerating dates all the way back to
Einstein and a person named Georges Lamatra, who was a Belgian monk.
And so those people were interested in the energy that makes gravity push rather than
pull, and they developed that theory really in the 1920s and 1930s.
Will people travel to Mars in our lifetime?
That is an interesting question.
It is certainly possible.
The question is how much it costs.
It's rather remarkable that when I was five, man last went to the moon.
Since the last 40 years of my life, we haven't been to the moon.
And the reason why is it's really, really expensive.
So I really think it's going to depend on how much people are willing to spend.
So I don't know if it's going to happen or not.
Time travel is possible, but only in one direction.
That is, if I want to move forward in time relative to someone else, I just need to travel
really, really quickly.
And so if I go to Alpha Centauri really, really quickly and come back, 8.6 years will
have elapsed here on Earth where only seconds will have elapsed for me, and in that way
I can travel forward in time.
But there is no way that we know of to go backwards in time.
As a Nobel Prize winner, my salary didn't suddenly go up.
It turns out I'm a scientist and I'm paid very, very well.
I'm not a millionaire, but I'm not poor either.
I have a very good salary and quite frankly I make more money than I want to spend, so
I actually give away a lot of my money every year for that reason.
The Nobel Prize itself was worth 10 million Swedish crown, which was about $1.4 million
Australian.
Now, I got a quarter of that.
And again, because I didn't feel I really wanted to go out and buy myself a Ferrari,
I'd rather let someone else do that.
I donated that money and I donated it to help some school programs for education.
I donated it to help build a building for science in Washington, D.C., knowing that
I'm a dual citizen.
And then a lot of the money I spent just to bring the entire team to Stockholm and to
celebrate our Nobel Prize.
So, right now, we are as astronomers looking all over the sky for planets.
It is my hope with the next generation of optical telescopes, one which Australia is
part of, called the Giant Magellan Telescope, that we will be able to potentially see the
signs of life during my lifetime by looking at a planet when it passes in front of its
star, and that means the light will shine through its atmosphere.
Now, as you know, here on Earth, we put all sorts of stuff into our atmosphere, like we
put in things that remove ozone, hydrofluorocarbons and things.
And those have very specific fingerprints, which we can see, and other types of life don't
make and aren't naturally created.
So, I think if there is a lot of life out there, we will see potentially signs of it
in the next 20 or 30 years with the next generation of telescopes.
It all depends on how much of it there is out there, and that's, I guess, one of the
reasons to look.
If a object is moving towards the speed of light, and you have, for example, a torch,
let's think of it from two perspectives.
Imagine I'm on that airplane.
Now, it turns out nothing can travel the speed of light.
It can only approach the speed of light.
But a fundamental part of Einstein's theory of special relativity, that's the one that
gave us E equals mc squared, is that the speed of light is the same no matter what you're
doing, no matter how fast you're going.
So if you shine your torch, the light will go away from you at the speed of light.
What happens if I'm looking at you from, you know, in the front, and that light is shining
at us?
Well, the light comes at you at the speed of light because, again, everyone sees the
speed of light be the same.
But because you're moving so quickly, you're shrinking the photons, you're compressing them,
and that makes the photons have higher energy.
And so it might be that if you're going fast enough, your torch will become a gamma ray
torch rather than just a light torch.
On the other hand, if you shine the torch backwards away from the direction of motion,
then if you're looking at that torch from behind, the light will be so stretched that
rather than being a normal torch, it will be a radio wave torch because radio waves
have much longer wavelength.
If you're going to travel the speed of light, it turns out you cannot have any mass.
Soon as you have mass, it is impossible to travel the speed of light.
And so massless particles, of which the photon is one, they can travel the speed of light.
Anything else can.
