Gravitational Waves, Cosmic What-Ifs & Dark Energy Dilemmas

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Andrew Dunkley: While the world takes a little bit of a rest

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over the Christmas New Year period. We

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thought we would, too. But we're not going to

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leave you hanging. We've dug into the

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archives and found a few of the biggest

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episodes of recent times. So sit

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back and enjoy those. And we'll be back with

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new episodes of Space Nuts, probably in

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the middle of January. See you then, Space

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Nuts. Hi there. Thanks for joining us. This

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is Space Nuts, Q and A. My name is Andrew

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Dunkley, your host. And coming up on this

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episode, we've got a question about

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gravitational waves and the Big Bang. We're

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also going to look, at a what if question.

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Love the what if questions. which is asking

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about, the life of Earth. Not life on

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Earth, the life of Earth. if

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the sun never died. Interesting,

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angle. And we're also going to look at, time

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and dark energy. That's all coming

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up on the Q A edition of space

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nuts.

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Generic: 15 seconds. Guidance is internal.

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10, 9. Ignition

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sequence time. Space nuts. 5, 4, 3,

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2, 1. 2, 3, 4, 5, 5, 4,

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3, 2', 1. Space nuts.

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Generic: Astronauts report it feels good.

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Andrew Dunkley: And joining me once again is Professor Fred

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Watson, astronomer at large. Hello, Fred.

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Professor Fred Watson: Hey, Andrew. How are you doing?

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Andrew Dunkley: I'm doing as much as I can.

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Professor Fred Watson: Good, good, good. Good to be Q and A with

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you.

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Andrew Dunkley: Yes, you too. shall we get stuck

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straight in?

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Professor Fred Watson: Why not? Yes, why not?

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Andrew Dunkley: All right. our first question comes. I'm not

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sure if it's BO or boa. I'll have to listen

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more carefully. Here we go.

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Beau: Hello, Fred and Andrew. It's Bo here from

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Melbourne. I hope you're well. I have a

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question for you. And it is not about dark

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energy, nor it is about dark matter,

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but it is about gravitational waves.

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It's a straightforward question. Did the

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Big Bang produce gravitational waves

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as we understand it? Gravitational waves, are

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generated when two massive bodies such as

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neutron stars and black holes collided with

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each other and cause that ripple in the

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fabric of space time. But

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when the universe has just

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began, infinite density and so forth.

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When it came into existence via the Big Bang,

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did it produce gravitational waves or echoes?

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And can we detect those echoes in space and

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time? Very much like the cosmic microwave

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background radiation that we see today.

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Anyway, I hope that made sense. I'd love to

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hear your answer. Thank you very much.

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Andrew Dunkley: Thank you. Boa. that's a good question.

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We talk about the Big Bang a lot. We get a

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lot of questions about it.

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and, I mean, it was

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a massive event. We don't know why

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we don't know a lot, but, we

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know we can see that it happened through the

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cosmic microwave background radiation that's

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still evident today. But

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gravitational waves would. I

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mean, if the universe didn't exist at

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the moment of the Big Bang and was being

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created as a consequence of that,

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I'm not sure gravitational waves could have

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happened the way we understand them with

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other events in our universe.

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I'm not sure about this one.

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Professor Fred Watson: So, the thing is, Andrew,

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Yes, the universe was created in that

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instant, of the Big Bang.

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and so you're right. you know, in the

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conventional theory, standard Einsteinian

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physics, we imagine that time

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and space didn't exist before the Big Bang.

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So, you've got to create some space for your

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gravitational waves to go through. which is

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kind of what.

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Andrew Dunkley: That's what I'm thinking.

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Professor Fred Watson: Yeah. And so, And so, yes, there

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was the instant of the Big Bang that

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created this singularity in

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time and space, followed by this

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period. Was it 10 to the minus 33 of a

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second, something like that in duration,

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which we call the period of inflation when

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the. When the expansion really

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took hold. and it, you know, the universe

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went from the size of a football to the size

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of a galaxy in something like 10 to the minus

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33 of a second. And,

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the thinking is, and I'm

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actually dragging this up from reading a few

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years ago, but yes,

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that inflationary period, as we call it,

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would have created gravitational waves,

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or maybe a gravitational wave.

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Andrew Dunkley: But I was about to say maybe just

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one big one at that point.

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Professor Fred Watson: But the issue is, that,

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it is a gravitational wave, a

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very, very, very low frequency.

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So, the gravitational waves that we get from

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colliding neutron stars, for example,

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they produce waves

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which are, basically have a frequency which

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is in the audio range. Which is why we can,

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you know, turn those, gravitational wave

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signals into an signal very easily

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after you've amplified it up a bit and after

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LIGO has done its magic on it. And that's

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where we get this chirp signal

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as two neutron stars, m or whatever, merge

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together, and eventually, because

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they're spinning ever more rapidly, and so

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the frequency goes up of the waves that are

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being emitted and then stop, at a high

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point because that's where they've coalesced

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into a single object. now

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you can think of those,

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audio frequencies. you know,

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we might talk about something like 500 hertz

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as an audio frequency. Or

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you could take 440 hertz as the frequency

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of, the standard, a note

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in the musical spectrum.

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so let's stick with 500 because that's an

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easy one. so the, the period

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of time between one peak of the

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wave and the next, is

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1-500th of a second. And so

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if you think that's the interval of time

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of a characteristic gravitational wave from

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two colliding objects. Now the

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issue as I understand it, is that

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the interval between peaks

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in a gravitational wave,

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produced by inflation

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is about the same as the age of the universe.

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Now it's not 1-500th

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of a second, it's you know,

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several billion years, perhaps even

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tens of billions of years. it's quite a while

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since I read up on this. So normal

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gravitational wave technology is simply not

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equipped to detect these low frequency,

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ultra ultra low frequency gravitational

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waves. But there might be other ways of

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seeing them. and one of the things people

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have looked for, and I'm not really

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very well up on this, but

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there is a potential signal

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in the cosmic microwave background radiation,

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the flash of the Big Bang that we see, that

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gives us what the Universe looked like

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380,000 years after the Big Bang. That's what

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we're seeing there. that

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radiation, contains information

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not just on its brightness, but also on its

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polarization. you know, that

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radiation is polarized, a bit like light can

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be polarized. And I'm not

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really drawing the links very

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strongly here, but I understand that there

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are links between very low frequency

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gravitational waves and that polarization

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signal. So it's one of the things that people

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are looking for to try and detect this

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polarization, within cosmic matter

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wave background radiation. So it's not at all

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a daft question, but it's quite a complex

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answer.

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Andrew Dunkley: Yeah, yeah, but the, the Big Bang itself

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could have initially been

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one created one gravitational wave.

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Professor Fred Watson: That's right, yeah. That's more or less it.

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Andrew Dunkley: M goa. you're right on the money.

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It's just a matter of finding a way of

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seeing them. is it possible these

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gravitational waves still bouncing around

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like the cosmic microwave background radio?

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Professor Fred Watson: Yes, yes, but at such a low frequency that

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you don't actually know it's there. You've

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got to find other, you've got to find other

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ways of detecting it because there's not

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going to be any change in the gravitational

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wave signal over, you know, a human

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experimental lifetime. If you've got

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a frequency whose time interval is measured

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in billions of years, forget it.

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Andrew Dunkley: Yeah, that's a tough one.

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Professor Fred Watson: Thanks.

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Andrew Dunkley: Boa. That's a great question and thanks for

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sending it in.

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we've got a question from one of our

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regulars, Rennie, who is from sunny West

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Hills, California. this is a what if

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question. Theoretically, if the sun were

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never to die, let's assum. Assume it's just

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never going to die. Would the Earth

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eventually erode, decay

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and die on its own?

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Professor Fred Watson: yeah.

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Andrew Dunkley: Well, my answer is no, because we'll destroy

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it first.

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Professor Fred Watson: It could be very different. I mean, so if

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what Ren is saying is that, yes, the sun, we

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know it's going to evolve over the next few

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billion years, and it will change and that

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will eventually result in the Earth being

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swamped by the outer atmosphere of the sun,

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which might not be very nice for anybody left

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on Earth. but if that

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didn't happen, if the sun just

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went on its merry way, being a normal star,

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there will be a few things that will happen

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over that time scale

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which we know won't happen because

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the sun turning into a red giant is going to

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overtake it. One of them is,

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the tidal

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breaking of the Earth's rotation so that it

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always, faces the Moon. So the Earth's day

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will change from

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24 hours to something like, if I remember

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rightly, it's 42 days, that it's about that

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length of time, and that's it turning once.

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And the Moon will go around the

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sky, around the Earth in the same time. So

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the Earth and the Moon will constantly face

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one another with ah, a month and a day, which

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are both equivalent to, I think it's about

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42, 43 days, something like that.

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so that's going to change things quite a bit.

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so that would certainly alter the

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atmospheric dynamics of the Earth if one

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side's getting warmed up for 20 days rather

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than just one day, of day and night. So

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a lot of things change. and yeah,

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the constant bombardment by the

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magnetic particles from the sun,

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I don't know to what extent the Earth's

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magnetic field might erode, but there will

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certainly be changes, may

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even be.

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Andrew Dunkley: What about.

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Professor Fred Watson: So go ahead, go on.

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Andrew Dunkley: No, I was just going to say if humans were

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still around in that period, would we.

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Well, okay, no, let me rephrase. Would we

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adapt as these things changed and

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reached that point? Would we be able to adapt

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as a species and other life on Earth, adapt

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to live in that kind of environment?

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Professor Fred Watson: Well, it certainly is. All these changes are

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ones that take place very slowly indeed. and

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over kind of longer periods than the

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characteristic evolution time to get

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from, you know, one mutation to another,

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whatever that might be for humans.

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so yeah, they're slow and

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I'm sure humans could adapt to them. we're a

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pretty adaptive species. We might also by

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then be capable of building the

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megastructures that might protect us from

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some of the sun's funny things going on.

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it's hard to know really, isn't it? But

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I think generally speaking, I mean, Rennie's

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question's a good. What happens if

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nothing happens to the sun? does the Earth

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just sort of survive? It probably

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survives. It will be changed. We might find

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we're all living in plastic domes or

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something by then, rather than because the

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atmosphere has been so messed about with. But

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yes, I think I'm an

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optimist that humankind would survive.

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Andrew Dunkley: Yeah, no, it's interesting because.

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Andrew Dunkley: I mean we know what's going to happen. We

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kind of know when it's going to happen. But

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if it didn't, it would create a whole array

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of new challenges for humanity because we

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would have to learn to live in a, very

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somewhat hostile environment, I imagine,

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because, the planet would not be the same

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and I can't imagine what it would be like to

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have a 42 long, 42 day,

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long day. well, you know, birthdays would

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be few and far between, wouldn't they?

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Professor Fred Watson: they would. But you, you know, we're gonna,

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we're gonna know what that's like very soon

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because the, the day on the moon is 20, you

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know, 29 days effectively from

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one right moon to another. So yeah, so

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we've, we've, we've already got something

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like that, in store for people to experience.

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It'll be very interesting to see what even

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the Artemis astronauts on the moon make of

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all that.

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Andrew Dunkley: Yeah, yeah, very interesting. Rennie, that's

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a great question. Thanks for sending it in,

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much appreciated.

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And next up we've got

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Daniel. this is a sort of dark

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energy question, sort of.

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Generic: Hey guys, Daniel from Adelaide here. There

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seems to be more and more discoveries lately

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in the very early universe that shouldn't be

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possible because not enough time has passed

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like size of galaxies or black holes. Now

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I've got a far out theory I'd love to share.

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What if time and dark energy were actually

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the same thing? So we know for about the

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second half of the universe that dark energy

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has been accelerating its expansion. Could

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this therefore mean that there was Less dark

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energy in the first half. And if that's the

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case, what if time actually went slower in

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the early universe? So from our perspective,

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what took a really short amount of time

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actually happened in normal time, with normal

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being in quotes. I'd previously asked the

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question on the show whether dark energy is

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related to black holes. I think there was a

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paper around the time that kind of suggested

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that it was. And we know, that black holes do

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distort time. So if time is part of the

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fabric of space, maybe dark

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energy is too. But it's actually one of the

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same thing. I'm expecting a very quick,

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simple no, but I wanted to ask anyway.

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Professor Fred Watson: Thanks. All right. Thanks.

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Andrew Dunkley: Daniel. yeah. Is, time and dark energy,

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are they the same thing?

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Professor Fred Watson: Yeah, you never get a quick and simple no

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from me, Daniel. It's always a long, drawn

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out complex. No, it's not always.

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I think in this case, yeah. Your thinking's

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interesting. we've talked recently as well

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about, the fact that

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this new controversial theory from Joe Silk

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et al, over in Baltimore,

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suggesting that perhaps black holes,

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supermassive black holes, came first, they

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were formed in the early universe. And that

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goes a long way to explaining, the conundrum

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that you mentioned at the start of your

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question there, that a lot seems to have

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happened in the first, in the first, few

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millions or hundreds of millions of years of

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the universe's existence.

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so we kind of understand

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the gravitational time dilation, effects

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pretty well. And they're actually quite

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small, from our vantage point

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here, 13.8 billion

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years later.

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But you're right to make the point that, dark

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energy only, seems to have appeared

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over the second half of the age of the

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universe. But that's more likely to be,

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because its measurable effect has only become

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apparent. We think that during the first

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half of the universe's age,

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the galaxies within the universe were close

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enough to each other. The gravitational

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attraction would have basically kept

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the expansion due to dark energy in check.

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The accelerated expansion, due to dark

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energy, and so it's only when you get

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past a kind of tipping point where

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suddenly the, the mass of galaxies in the

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universe is not enough, not strong enough

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gravitationally to break the

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acceleration of the expansion. By that I mean

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B R A K rather than B R E A K,

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it's not enough to slow it down and so the

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acceleration takes over. and that's why

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it's a tricky thing just to try and

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tease out. And we've talked about this

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recently as well. Whether the, dark

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energy is a constant, whether it's something

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that's a, factor that

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hasn't changed in terms of, its release

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as space expands. it's because there is

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this added impact of the gravitational pull

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of the galaxies, stopping us from basically

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seeing the effect of dark energy, the

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accelerated expansion of the universe back in

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the early universe. So I think all those

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things are well and truly understood and

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kept fairly separate by the scientists

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looking at them. And by that I mean time and

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dark energy. So that's a long, complicated

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move.

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Andrew Dunkley: Yeah, yeah. okay. Daniel

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Winfred says, I think these things have been

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long understood. That's his way of saying,

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you're way off, way, way

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off the mark.

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Professor Fred Watson: Go on.

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Andrew Dunkley: But it's worth asking because otherwise,

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obviously this is something people are

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thinking about. So it's worth asking,

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these different questions

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to, just see if it's a

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possibility. Thanks, Daniel. Appreciate that.

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Professor Fred Watson: Great question.

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Andrew Dunkley: if you've got questions for us, please send

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00:17:49.452 --> 00:17:51.292
them in because we could always use them.

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00:17:51.782 --> 00:17:54.662
just go, to our website, spacenutspodcast.com

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00:17:54.662 --> 00:17:57.542
spacenuts IO and click on the various links.

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00:17:57.542 --> 00:18:00.492
The AMA link will give you, access to,

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00:18:00.902 --> 00:18:03.792
text and voice, audio. Or you can

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00:18:03.792 --> 00:18:05.792
click on the little. It's not purple, it's

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00:18:05.792 --> 00:18:07.192
green. When did they change the color of

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00:18:07.192 --> 00:18:09.962
that? send us your. Oh, no, it's. It's purple

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00:18:09.962 --> 00:18:11.792
when you hover on it. There you, go. send us

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00:18:11.792 --> 00:18:14.142
your questions, on the right hand side of our

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00:18:14.142 --> 00:18:16.542
homepage. And don't forget to tell us who you

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00:18:16.542 --> 00:18:18.702
are and where you're from. Fred, we're done.

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Again, thank you so much.

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Professor Fred Watson: always a pleasure, Andrew, and I hope we'll

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see you then very, very soon.

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Andrew Dunkley: It's a distinct, possibility. Could

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be within 13.8 billion years, in fact.

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Professor Fred Watson: Yes.

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Andrew Dunkley: Thanks, Fred. See you soon. Fred Watson,

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astronomer at large. And, thanks to Huw in

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the studio for making our lives so much more

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00:18:38.282 --> 00:18:40.882
difficult with these split episodes. But, no,

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00:18:40.882 --> 00:18:43.332
it's okay. and from me, Andrew Dunkley, thank

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you so much for joining us. Looking forward

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to your company on the next episode of Space

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Nuts. See you then, Space Nuts.

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00:18:50.372 --> 00:18:52.572
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