Andrew Dunkley: Hi there, this is Space Nuts.

Q and A.

My name is Andrew Dunkley.

Great to have your company.

Coming up on this episode, we'll answer questions from Steve, Gus and Nick.

Uh, Steve and Gus are sort of focused on the same thing, gravity.

Steve, uh, wants to know if it can exist without mass.

Uh, and Gus is talking about gravity and energy and what's the relationship.

And Nick is asking about galaxy, um, movements and are any moving towards us that we can't see yet?

Well, we don't know we can't see them yet.

Uh, but we'll see if we can tackle all of that on this episode of space nuts.

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Space nuts.

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Space nuts.

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Andrew Dunkley: Here he is again, Professor Fred Watson.

Hello, Fred.

Professor Fred Watson: Hello Andrew.

Hello.

How are you doing now?

Andrew Dunkley: I'm doing the same as I was before.

How about you?

Professor Fred Watson: Uh, well, I'm still doing the same as I was before.

Yes, that's right.

And I hope to be doing the same again very soon.

Andrew Dunkley: Yes, indeed, yes.

Uh, shall we just sort of muck in and get these questions sorted out?

It was ah, like a couple of weeks ago we had um, gravity questions coming in thick and fast.

Uh, no black hole questions.

But today it's gravity questions.

Professor Fred Watson: It is.

Andrew Dunkley: And our first one comes from Steve.

Steve: Hi guys, my name is Steve.

I'm uh, from New Zealand.

Um, really enjoy your show.

Recently read a article implying that, uh, gravity could be possible without mass.

And um, I'm wondering if that would be, uh, another alternative explanation to um, uh, dark matter and to Mond.

Yeah, I don't know if that makes it very clear to you.

Anyway, thanks.

Andrew Dunkley: All right, uh, Steve, thanks for the question, gravity without mass.

Well, I doubt that, uh, we can turn to the Catholic Church because they do have mass.

Um, but, uh, terrible.

Uh, it's an interesting question though.

Professor Fred Watson: It is.

And um, so yeah, my reading on this.

Excuse me, is yes, um, that's correct.

So, uh, actually there's a nice thread about this on Reddit if anybody looks at that website.

Andrew Dunkley: I do.

Professor Fred Watson: And um, well, I love Reddit.

Yeah, really Well, I do remember my, uh, one of my sons was an absolute Reddit fiend at one time.

He was very much, um, a Reddit fan.

Uh, now, so that's how I was aware of it.

But I haven't been a great user of Reddit.

But the bottom line.

Excuse me, is, um, and this is the way it's phrased in this Particular conversation.

If you increase the temperature of an object and they take a planet, in this case, uh, and in fact I might just read it, uh, because this kind of is quite interesting.

Um, take your Neptunian planet, something the size of Neptune, raise the temperature by 300 degrees Kelvin instantly.

Now, the mass of neptune is about 10 to the 26 kg.

And if we roughly assume all its hydrogen, uh, corresponds uh, to about 6 times 10 to the 52 particles of hydrogen.

Uh, the thermal energy is roughly given by an uh, equation.

There equals nkt, uh, uh, which leads to an increase in thermal energy, uh, of deh.

Gus: Duh.

Professor Fred Watson: Uh, and it's a large number of joules.

Um, actually it's a small number of joules.

It's k times 6 times 10 to the minus 52 times 300 Joules, which um, if you then convert that.

So what this is saying is you warm up a planet, you get an increase, uh, in the thermal energy of that planet.

You can then use E equals MC squared to convert that thermal energy into mass.

And in this case it comes out to be something like 3 times 10 to the 15 kilogram is a lot, but, uh, is not very much in comparison with a planet.

Uh, but that does mean that adding energy to something will increase its gravitational mass.

Now, um, Steve's sort of, uh, you know, um, next step in the argument from that is whether that could be misleading us in the idea of dark matter and things of that sort of.

Um.

And uh, I can't really get my head around how that would work.

Um, he mentioned MOND as well modified Newtonian dynamics.

Um, because my understanding is that everybody who looks at these particular problems, what is dark matter?

What is dark energy, they take into account everything.

Uh, I've um, read some of the papers on this and so things like, um, uh, gravitational influence of pure energy.

And in this case we're talking about heat energy.

That uh, is likely to be something that would be already in the equations.

Um, so I don't think it's the answer, but it's a really interesting suggestion and an interesting thing to think about.

Uh, thank you very much, Steve.

Andrew Dunkley: Yeah, indeed.

Just, um, made me wonder.

Are we increasing Earth's gravity because we're heating the planet up?

Professor Fred Watson: Yep, that's probably right.

Um, I mean the example that uh, I just read out was about 300 degrees Kelvin, an instant increase, uh, in that we're talking about one or two degrees Kelvin, uh, uh, which makes a big difference to the Earth's atmosphere, but probably not that much difference to its uh, you know, gravitational potential.

Andrew Dunkley: Okay, M.

So the answer is yes.

Gravity can exist without mass, but it's probably not a major factor.

Is that fair enough?

Professor Fred Watson: Uh, yes, that is right.

Um, I've, uh, just been dragging through my memory, Andrew, something else that's sort of vaguely related to this.

Um, which is the.

Well, we haven't used this name, but we did talk about it a while ago.

Kugelblitz.

Do you know what a Kugelblitz is?

Andrew Dunkley: Uh, look, I've heard this before.

Uh, no, remind me.

Professor Fred Watson: Yeah.

So it basically is, uh, a black hole made of light.

Uh, and Wikipedia says it's a concentration of heat, light, or radiation so intense that its energy forms an event horizon and becomes self trapped.

In other words, if enough radiation is aimed into a region of space, the concentration of energy can warp space time so much that it creates a black hole.

It's a black hole as a black hole whose original mass energy was in the form of radiant energy rather than matter.

Uh, now, um, there is a paper that was published in 2024 that concludes that a phenomenon like this cannot occur in any realistic scenario within our universe.

So kugelblitzes, uh, are a theoretical entity that are not thought not to occur in nature.

Uh, but it is a similar thing, isn't it?

So it basically.

It's a black hole made of energy.

Andrew Dunkley: Yeah.

Wow, that's really interesting.

I'll tell you something else that does exist is a Kugel scriber.

So I've got one of those.

Professor Fred Watson: Have you?

Andrew Dunkley: Yeah.

There it is.

Professor Fred Watson: Mangle.

Andrew Dunkley: It's a pen.

It's German looking.

Professor Fred Watson: Hold it up.

Ah, okay.

Andrew Dunkley: Google scriber.

Professor Fred Watson: Kugel scriber, yes.

Andrew Dunkley: You know what German is?

Uh.

You know what the German is for pencil?

Professor Fred Watson: Uh, I probably did once, but I don't know.

All right.

Uh, it's probably.

I only.

Andrew Dunkley: I did languages at high school, and I was very good at them.

And I should have probably pursued that somewhere along the line, but German stuck with me.

Professor Fred Watson: I.

Andrew Dunkley: Some of the references I still remember today.

Someone's going to correct me now because I probably buggered up the, uh, pronunciation anyway.

Professor Fred Watson: That's all right.

Andrew Dunkley: I'm just showing off now.

Professor Fred Watson: No, ah, it's a side of your character that I was unaware of, Andrew.

Um, curiously, I, uh, never joined Lerman at school.

I never learned Sherman at school.

Um, but, uh, uh, when I was 14, uh, I went on a school exchange to Germany, which was Barbara, because I wasn't studying German.

But that was my first overseas visit, of course, from the United Kingdom.

Um, and so I've spent the.

However many years it is, 60 odd years since then trying to learn German and.

Andrew Dunkley: Yeah, yeah, look, I'm so jealous of students in countries like the United States and the UK and Europe because they get to do excursions to other countries.

In Australia, we got to do excursions to Sydney and Canberra.

I mean, come on.

That was it.

Yeah, that was as good as it got for us.

Yeah, I mean, these days they get to go to New Zealand once in a while.

Um, but yeah, we're so far from everywhere.

It's just not easy.

Although my son did go to get to do a couple of weeks in Japan through high school.

Professor Fred Watson: So there you go.

Andrew Dunkley: There are a few options these days.

This is Space Nuts.

Andrew Dunkley here with Professor Fred Watson.

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Andrew Dunkley: Space Nuts.

Uh, we better keep moving.

Uh, thank you, Steve.

Let's get a question from Gus.

Gus: Hello, Professor Fred and uh, Andrew.

Uh, this is Gus Iverson from Issaquah, Washington.

I sent in a question for you guys previously and you thought I was in Western Australia.

Yes, I, I've been thinking about, um, gravity, uh, today.

And it, it came to my mind that if, uh, energy and mass are equivalent, then essentially, uh, shouldn't energy also create gravity at some level?

Um, I'm not sure if this is a related question or an extension or a separate question though.

Um, uh, additionally, um, if a body of any size is generating or has mass and it is generating a gravitational field, does not that field itself have energy and mass?

And would that field not create additional gravity by its simple existence?

So if that's the case, or even kind of the case, my question is, where does the energy and mass go?

If, um, or, um.

I have no idea where to go with this.

Professor Fred Watson: Thank you.

Gus: Uh, I love the show and, uh, appreciate being able to ask questions.

Andrew Dunkley: Thank you, Gus.

Uh, that sounded very much like something from catch 22.

Was it apples or tomatoes?

They were trying to.

I don't know.

Um, but, uh, yeah, it sounded a bit like that.

Um, gravity plus energy, body plus mass plus gravity equals energy.

But then does that add mass which adds to gravity?

I think that's what he was trying to.

Professor Fred Watson: Yeah, that's right.

So, so you've got a.

You know, the whole thing gets completely out of hand because everything's got gravity.

Um, I think, uh, so the first part of what Gus was saying is what we've just been talking about.

You know, if you have energy and mass, um, and gravitation, you probably have to be careful with the words.

Gravitation is a Potential.

Uh, an object in a gravitational field has potential energy, so it does have energy.

Uh, but I kind of need to take this one and notice.

Actually, you did give me notice, Andrew, but I didn't have time to really look further into it.

Andrew Dunkley: But.

Professor Fred Watson: I think there's a stumbling block somewhere in that argument, uh, which is probably that gravitational energy isn't energy.

That's convertible to mass.

Um, but I need to get my thoughts clearer on that, which they aren't at the moment.

So, Gus, thank you for a very, uh, tricky question, uh, which, um, I might think a little bit more about.

Uh, and, uh, perhaps we will revisit it in a future episode of Spacenuts.

Q and A.

Andrew Dunkley: Um, I put a, uh, homework marker next to it.

Professor Fred Watson: That's what I.

I'm just doing that.

I'm doing it.

You're doing it in your, uh, kugel.

Andrew Dunkley: I'm using a red Kugel scriber.

Professor Fred Watson: Okay.

Andrew Dunkley: I don't know what the German word for red is, though.

Professor Fred Watson: Oh.

Andrew Dunkley: Probably do it on translator.

Professor Fred Watson: Uh.

Andrew Dunkley: Ah, there you are.

Professor Fred Watson: Yeah, there you are.

Andrew Dunkley: I don't have to look it up.

Professor Fred Watson: You do.

Andrew Dunkley: So, Gus, um, dunno.

We don't know.

Maybe.

Possibly.

Could be.

Professor Fred Watson: Don't know.

Yeah, but we'll.

How's that?

Andrew Dunkley: Don't yet know.

I like that.

Professor Fred Watson: Yeah.

Andrew Dunkley: Uh, let's, um, get to the final question.

We'll get back to you, Gus.

At some stage in Western Australia, or it could be the United States.

Uh, now we've got a question from.

Oh, um, just by coincidence, from New Zealand again.

Um, hi, Tim.

Amazing podcast.

Which one are you talking about now?

Uh, I have been listening since your early days and have always, uh, looked forward to new, uh, uploads.

My question is around the discovery of early galaxies from the James Webb Space Telescope.

Is it possible for earlier galaxies to be traveling towards us that are currently out of reach?

Uh, filling with potentially, uh, nothing.

Uh, filling where potentially nothing was in view before.

Uh, if possible, would the light be compressed?

How would the instruments deal with that?

Hope that makes sense.

Cheers.

Nick from Auckland, New Zealand.

My brain just went, well, I suppose it's possible, but how do we prove it until it happens?

Professor Fred Watson: Yes.

So, a.

Ah, couple of things in here.

Um, thanks, Nick.

Great question.

The last bit about light being compressed, um, and in a way, that's, um, quite a nice way of putting it.

So anything that comes towards you that's emitting light, its light will be blue shifted.

In other words, its wavelength will get shorter.

And that's saying it's compressed is pretty well you know, that's pretty well what happens.

It's like, uh, um, you know, the good old ambulance, uh, siren or fire engine siren or whatever it is coming towards you, uh, which compresses the sound waves.

And the result is an increase in pitch.

Which corresponds to a shortening of wavelength.

So that's standard physics.

We can detect, uh, by the Doppler shift, anything coming towards us.

Uh, by the fact that its light is shifted towards the blue end of the spectrum.

Um, but, um, the first bit of the question about galaxies, earlier galaxies traveling towards us.

Andrew Dunkley: Um.

Professor Fred Watson: When we think about galaxies, we have two different velocities involved.

One is the velocity of a galaxy as it's carried along by the expansion of the universe.

Uh, and that is what we measure as a redshift.

Uh, the expansion of the universe is carrying galaxies away from us.

And so their light is being redshifted.

Uh, and by the time you get to these really early galaxies where you're looking back, uh, almost the whole edge of the universe, the redshift is very considerable.

It's a factor of 13 or 14, something like that.

We're giving the name Z.

Uh, the redshift is about 14.

So, um.

I beg your pardon.

No, that's not true.

Uh, that's me confusing the age with the redshift.

Forget that bit.

But the number's quite high.

The redshifts are probably five or six or something like that.

But, uh, it's still a high level of the light being stretched out by the expansion of the universe.

So that's one velocity.

But galaxies can have superimposed on that a velocity which we call a peculiar motion.

Its own velocity, uh, caused by local eddies in space or whatever.

Uh, that.

That might, um, move a galaxy towards us.

It's the gravitational field that it's exposed to.

Very much like the analog is always a river carrying you along.

Uh, and if you're in a rowboat, you can move relative to the river.

But the river's always carrying you along.

That's exactly what's happening with the Hubble flow, the expansion of the universe.

And these peculiar motions are superimposed on that.

But they're much, much less than the motion, uh, those distances, uh, or look back times.

It's much, much less than the expansion flow of the universe.

So no, there won't be anything hidden from us that's coming towards us.

I don't think it's an interesting suggestion.

But, uh, uh, everything's moving away from us at this very high velocity.

At those distances, M of Course.

Andrew Dunkley: Um, Nick, if you want to check with us, uh, in a million years or so, we might have an alternative answer.

Professor Fred Watson: Well, that's true.

Uh, put that in your diary and, uh, I'll mark it with an asterisk, knowing that it's work for a million years time.

Yes, it's good.

Andrew Dunkley: Um, I'm really disappointed that the people who make diaries haven't gone ahead that far yet.

Thanks, Nick.

Um, probably not, I think, is the answer.

Um, but thanks for the question.

Thanks to everyone who sent in questions.

Keep them coming.

You can do that via our, ah, website spacenutspodcast.com spacenuts IO which, uh, has two options.

The AMA tab at the top where you can send us text audio or the send us your questions, um, button on the right hand side of our home screen.

Don't forget to tell us who you are and where you're from.

And you can probably upload your audio questions on any device as long as you've got a microphone.

Mobile phones are perfect for this.

Um, but, um, a lot of people have home computers with mics built in, et cetera, et cetera, et cetera.

Always happy to hear from you.

Um, Fred, thanks so much.

We're done with another episode.

Geez.

We're wrapping them up.

Professor Fred Watson: We are racking him up.

Good to talk to you, Andrew.

And we'll speak again soon.

Andrew Dunkley: Indeed we will.

Professor Fred Watson, astronomer at large.

And thanks to Huw in the studio for collating.

Not much, but, uh, we thank him anyway.

And from me, Andrew Dunkley, thanks for your company.

See you on the very next episode of Space Nuts.

Bye bye.

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