How old is the universe?

People might know it.

13.8 billion years.

What is that number come from?

Ah, nde.

There's a little bit of a interesting difference emerging that might stand the test of time.

And if it does stand the test of time, it either means we're not understanding what we're doing, or there's perhaps some new physics out there that we've not really accounted for yet.

And that, of course, is the latter would be very exciting.

So how do you measure something as vast as the universe like, Where do you stop?

So we think of our universe is evolving in time on Dorothy special sections, and we're living in a part of it on DHF of large distances.

The distant Galaxies will be actually moving apart.

You can figure out, you know, how far is that thing and how fast is it moving away from May and then rewind time?

Then you can figure out how long the universe has been expanding for, so essentially it boils down to sort of speed equals distance over time, Really.

I mean, there's a lot more of complications in there because we actually know that the universe is accelerating, expanding and not just expanding.

It's getting faster all the time and then also the sort of effects of general activity when you bring in really, really distant objects.

But basically speed equals distance over time.

We can either measure it by looking at Galaxies that are not that far away from us on determining how they're revolving with respect to one another.

And we thes we do these music well, when I say not that far away from us, I have to be a little bit careful.

Some of these Galaxies we're looking at about seven billion years old, so they are a hell of a long way away from us to mention this.

You obviously conscious he's one object you need.

A lot of them need to statistics to be good.

So let's start with distance.

Okay, so how do you measure the distance of an object again?

It uses a concept that people might be quite familiar with.

So used this idea of a parent brightness.

So if you're crossing the street at night, left right, green cross code or that but you'll see a car headlights coming towards you and you'll know whether it's safe to cross because you know how bright car headlights normally are when they're right near you and you'll say, OK, well, it's not that bright and so I can figure out that it's far enough away that it's safe for me to cross.

So I started was basically used the same concept and they say, Okay, we need to find something that we know what brightness it should be and how bright it appears could tell us how far away it is by looking for what we might call standard candles in them.

And these are the supernova, the typical ones.

Type one a supernovae in tight.

What do you have?

A binary star system.

One of them will have reached the end of its life and have gone normal.

Supernova.

Okay, on what it left behind is it's cool, which we call the white dwarf would probably still be glowing somewhat more.

That white dwarf is sort of held up by.

Is this thing called electron generously pressure that the whole thing is held up by the fact that the electrons don't want to push any closer together?

The other star, though meanwhile, is sort of still orbiting around it, okay, still in its sort of normal life cycle.

But eventually it will start to run out of hydrogen, and it will swell to what we call the red Giants.

And then that's probably gonna come into sort of the sphere of influence of this little white dwarf on that white dwarf is going to start sort of accreting that material from that other star.

And then it's gonna keep building up mass on building up its mass until it reaches the point where those electrons being pushed together can't support anymore on.

Then it will go supernova in this type warning.

Again.

Again.

Yeah, supernova Twice.

Pretty cool.

But I think it's because of that electron generously pressure because electrons are the same across the entire universe, that mass that it reaches 1.4 times the mass of the sun is the same everywhere.

Therefore, it's always going to explode with the same energy.

So from that you can calculate the distance quite easily, knowing that their brightness is doomed so much over that distance.

How do we know the supernova?

We're looking at these talks.

Yeah, Good question.

So it'll the type one AIDS have a very distinctive signature in their spectra.

So not just the all of the light we receive.

If we take that light and split it through a prism, when we look at its constituent parts, they'll have a very specific signature in its elements.

So first of all, you have to be able to recognize what type is.

And then you could say OK, so how bright does that appear now?

So it's all about because these things happen really quickly and start to fade really quickly.

You have to have sort of, like, really quick response times for telescopes to be able to figure out what these things are.

So you see a type one go off in a galaxy, you know how bright it should be.

You know how bright it looked.

And that tells you how far away that whole galaxy is exactly.

Yeah, it's really difficult to tell the distance to Galaxies themselves because you have no idea what size the galaxy could be.

And you know it could be the same size Milky Way might not be.

It might be bigger and smaller, and so when you have a supernova that's then bright enough to outshine that entire galaxy.

You can then put a distance on that.

So now we need the speed.

Oh, Christ.

We need to know the speed that this galaxy that this supernova is residing in is moving away from us again.

We use a handy little phenomenon called red Shift.

Okay, so people might have heard of this before.

It's this idea that because the universe is expanding, the light that's given off by that supernova will be stretched as it travels across that space.

Okay.

And it will be shifted and lengthened toe longer.

Waveland, Soto read a Waveland since Red Shift because it is being stretched, we can then say OK, we can convert that into a speed at which that that is moving away from us, similar to a Doppler shift so we can turn a red shift of, say, 0.5 into a recession velocity.

And again, you're gonna need the spectra of that supernova, not just to identify that it is a tight one, eh?

But actually look at the light, see how much has been shifted by and therefore calculate the speed that it's moving away from us.

Basically, what we're gonna end up with, I'm gonna draw.

This is very exciting.

And you end up with a nice plot of your distance.

Could be in a really weird unit that astronomers like Called a mega Paszek.

She's a distance, not a time.

Thanks.

Stalls.

And then you're gonna have it against, basically, red shift, which will be in be translated into a speed in kilometers per second.

And what you end up with You gonna measure this for as many supernovas?

You can and you end up with them all.

Sort of dotted like this.

Emails drawer.

Nice.

Best fit line through them.

Okay, Because what you'll see is that your velocity that you're receiving out is gonna be proportional to your distance.

That's nice correlation there.

So actually, what?

We end up calling this proportional constant is the Hubble's constant or hate.

Nor here like that.

And this hate, nor is going to basically be in kilometers per second per mega Pasic.

Okay, so you know, if this is a distance, this is a measure of distance.

So really, if we put those in the same unit So we canceled them out, it really being one over seconds.

And so if we do one over hate nor gonna end up with something that's in seconds which will give us age of the universe a time in seconds, seconds, there is a lot of uncertainty in this method.

How do you know also that you're getting the right value?

What you ideally needs is another method to be able to confirm whether that value you're getting is right or not.

With supernova, the current supernova camp is saying that the Hubble's constant is 73.2 full kilometers per second for my composite on.

Then there's another way there.

There are a number of ways.

But the second way, which I think is particularly interesting, is by looking at the very early universe on looking at the fluctuations in the temperature of the universe due to events that occurred at the very beginning of the universe may be due to inflation.

Report officials.

Andi you can look at the hot and cold spots and look at the radiation that's emitted in the turn and it reaches is in the microwave background microwave range.

So it's called the cosmic microwave background Radiation.

Now you can fit the hot and cold spots.

The distribution of these temperature fluctuations with a given cosmological model.

You pick your cosmological model and you see how well it fits The debt on the best fitting cosmological model is called the Lambda CD and Model Lambda.

As in the cosmological constant, it gives you a value of hedge note today, which is about 66 kilometers per second per mega par sec.

So you think, Come on, that close enough ones Measuring the universe is a za result of physics that we're seeing that occurred 300,000 years, 380,000 years after the Big Bang one is much more recent seven billion years or so after the big bank on you, within 9%.

The issue is this, that the each of the sets of people that have been doing these measurements of working very hard to understand the uncertainties in their measurement on the uncertainties, both in their experiments, systematic uncertainties, and they've both now reached the stage where they era bars of each don't overlap with one another anymore.

So there's been a lot of contention for a very long time about what value is actually right.

Hubble's constant and ideally, what you want is a completely independent measure.

We didn't have that for a very long time until 2017.

So in 2017 there was a neutron star neutron star collision detected by the Lego in Vega Collaboration on the really cool thing about it was that there was also an optical detection of the same event.

Okay, so not only did you check the gravitational ways, we detected it in optical and gamma and X ray.

And all of these different electromagnetic spectrum radiation was really exciting.

But it also meant that it became what's known as a standard siren.

So understand a candle or sounded ruler astounded siren.

So something that you know how loud it should be.

And then you can compare it to how loud you observe it to be.

So from the gravitational waves we go, how loud is it supposed to be compared to what I model it to be?

And then from the light that we detected, we again got a red shift and therefore we could know its distance.

So But you're dying to know what value they found?

Yeah, And if they solved the whole mystery.

Yeah.

Okay, So here's the paper Gravitational wave, standard siren measurement of the Hubble constant.

And this is what people have been waiting for and cosmology for years.

And I guess you want to see the plot.

This blue line is what they got from the Bionic.

Accused two constellations with their standards.

Rulers, this is what you got from standard candles of supernova.

And then this line here is the likelihood of the Hubble constant being that value Given this not this one neutron star collision and can you see right where it falls right in the middle at about 70 kilometers possession from a composite.

I know it's so annoying.

Could still people were waiting for so long.

As soon as people heard that this happened, they like constant.

We're finally gonna know it was just right down the middle.

So far is one measurement, of course.

And so I'm sure I assumed I think there's some bigger balls on it for it to become a significant player.

Then you've gotta have lots and lots of neutron star mergers from which you can then build up the statistics.

From what I recall for the next few years, they're not expecting to see very many of order one a few a year.

Well, that means you're gonna be waiting 10 2030 years to build up significant statistics on it.

We're basically in a waiting game now to see what happens with this and whether we can actually be sure of what the Hubble's constant is or not.

The equation Tau work out when the time when it began is trivial.

It's a really trivial requires the only consistent two terms in it on one.

But one of them's the evolution of the Hubble parameter.

Hey, Chin daughters, its value today, but it evolved in time on the way it evolved in time depended on what's in the universe.

And that's the thing people are trying to pin down.

You know how much of it is matter how much it is cold up matter ham, a budget of his dark energy?

How much is in the curvature of space time on different combinations of those three will give me a different edge to the universe.

Calculate it yet.

Okay, let's get it.

Yeah, T, what's your time of your universe is going to be won over your measurement for the Hubble's constant into the Hubble constant that the lie go team found waas 70 plus 12 minus eight because there wasn't very precise kilometers per second Omega Pasic.

We're gonna have 1/70 basically.

So one mega par sec is 3.86 times 10 to the 22 meters.

That value is bent on your break if you've done.

And I started to degree ever before.

Okay, so what we're actually gonna do is we're gonna be one divided by 70,000.

But you made it into meters in case that's meters per second.

And then divide that by 3.86 times 10 to the 22 meters.

Okay?

And then you be thankful to him that I did that calculation before and it waas 4.41 times 10 to the 17 seconds.

So let's turn that into years.

Okay?

So if we divide it by 60 we get it in minutes.