Ask Me Anything AMA with Astrophysicist Dr. Joe Pesce!

[DrJoePesce]

Eek, I should've seen that.

So is it mainstream that over 4.5 billion years that planets have moved outward from the Sun due to expansion? Or do they simply keep their orbiting distance ignoring the infinitesimal daily expansion? It's interesting to me to favor the latter view in a Newtonian universe, but the former view may be favored where the planet is seen to simply travel along an expanding geodesic. But the spacetime gradient, I assume, will remain the same and the planet will, seemingly, just ignore expansion and stay in that region since the gradient isn't expanding to allow a more distant geodesic. Is there a favored mainstream view?

Given a continued acceleration rate for expansion, of course at some very distant time, the daily expansion rate will overpower all the rest. But that seems to me to be a different circumstance than today, or is it all the same just far less noticeable now?

Currently, expansion is occurring on the small scales, but it's well-below the sub-atomic scale so isn't noticeable or relevant. But the expansion is unrelenting, and space is stretching, so over trillions of years the expansion, even on the smallest scales, will be relevant.

Take a sheet of rubber and, with help, pull on all sides equally. Observe the center: There is little stretching there, with most of the stretching happening on the edges. But as you continue to pull the sheet, eventually even the stretching at the center becomes visible.

 

[DrJoePesce]

Remarkable! I really like the element progression. Mendeleev would love it!

[One nit.... it is stated, "... all the elements of the natural world have appeared and now continually recycle and reprocess." This sounds like something out of the Steady State theory. It is way too rare that hydrogen is recycled due to helium fission or whatever.]

Thanks Helio - I'm glad you enjoyed the video. I think by "recycle" the meaning is that elements created in high mass stars are returned to the interstellar medium when the star explodes as a supernova. That material then goes into the next generation of stars - it's recycled. It's not that elements are broken apart and then recreated.

 

[DrJoePesce]

I am super-excited on seeing you back, Dr. Joe Pesce! I would like to ask you a couple of questions.

1) When will we be able to get a clearer picture of a blackhole? Will we ever?

2) We know, blackholes contain in their centres, theoretically speaking, singularities, points of zero space with mass in it, creating infinite density. I am going to take an example of a stellar-mass blackhole because I don't yet know how a supermassive blackhole is created, I doubt if anyone else does. As we know, a stellar-mass blackhole forms when a gigantic star implodes. But I doubt how it can implode to a point of zero space, that would take forever! Just like it would take forever to reach absolute zero! So, what do you think, what is a better alternative for a singularity? And what about Planck stars? You can consider this a continuation of a previous question asked by me in the last AMA.

It's my pleasure to be here with you IG2007, and I'm excited by all your questions!

1) The Event Horizon Telescope will continue to observe the region around the black hole in M87, and other objects. So, yes, we should get better and different types of observations. (And note I say "region around the black hole" because, by definition, we can't see the black hole itself!).

2) If I may, I would like to correct your terminology a bit: The star isn't really imploding but collapsing on itself. The mass is so great, and the collapse is so violent, that the singularity forms.

 

[DrJoePesce]

Hey Joe, great to see you here.
What laws or principles of physics prevent you from creating or destroying spacetime?
We observe it expand, contract, and twist, so why not create or destroy?

This outside my area of expertise; but space just is!

We could have a collapsing universe where space (and the matter and energy it contains) gets smaller, denser, and becomes a singularity (this is probably not going to happen to our universe). But it's still there within the singularity, presumably. On the local scale I don't think you can destroy it since that part of the universe would cease to exist (I guess!?).

 

[DrJoePesce]

Hey Dr Joe
We have just seen images of the black hole in M87 from multiple telescopes and they are fantastic. The relativistic jet exploding out of the SMBH has polarized lines in it with the signature of magnetic fields. Could they be the space-time continuum?

Hi JSNardello - aren't those polarized images terrific? This is my area of research, and we've known for some time there must be strong magnetic fields present, and they probably have something to do with the jet, but it's always nice to get more information, and especially at this ultra-high resolution.

For those of you wondering what we are talking about, see this terrific article by my great friend and colleague, Chelsea Gohd: https://www.space.com/first-black-hole-image-polarized-m87

To you question: No, I think this is just the magnetic fields showing themselves on the plasma in the accretion disk and jet (much the same way as the magnetic fields on the sun do - to different scale and probably mechanism: https://nso.edu/press-release/inouye-solar-telescope-releases-first-image-of-a-sunspot/)

 

[Helio]

Take a sheet of rubber and, with help, pull on all sides equally. Observe the center: There is little stretching there, with most of the stretching happening on the edges. But as you continue to pull the sheet, eventually even the stretching at the center becomes visible.

Agreed, and thanks for you continued assistance.

But put two proverbial bowling balls on a trampoline and continue stretching the elastic fabric from the sides of the trampoline. Those bowling balls will stay together. With acceleration of the fabric, however, at some crazy future rate, the balls will separate. I would have thought this analogy would apply to planets orbiting the Sun. Apparently that's not the view of mainstream science.

 

[DrJoePesce]

Agreed, and thanks for you continued assistance.

But put two proverbial bowling balls on a trampoline and continue stretching the elastic fabric from the sides of the trampoline. Those bowling balls will stay together. With acceleration of the fabric, however, at some crazy future rate, the balls will separate. I would have thought this analogy would apply to planets orbiting the Sun. Apparently that's not the view of mainstream science.

Planets orbiting the sun, and eventually electrons orbiting atoms, will all be separated from each other in the far distant future due to the universal expansion. Even further in the future, subatomic particles will be ripped apart as well.

 

[Timesemit]

Here on Earth, lodestone, like any magnet, has 2 polarities. Is this because Earth has 2 polarities? Would native lodestone on Jupiter have more than 2 polarities?

 

[Helio]

Planets orbiting the sun, and eventually electrons orbiting atoms, will all be separated from each other in the far distant future due to the universal expansion. Even further in the future, subatomic particles will be ripped apart as well.

Yes, we agree on this because endless acceleration in the distant future will not be so kind to things.

But I'm trying to get a feel if there is a consensus with cosmologist as to the expansions effects relative to the other forces. Perhaps this will address my question better...

Is it your opinion that the expansion, say over the last 12 billion years, has separated all objects, even the orbital distance of an electron around a single proton in an isolated patch of space? If we could go back in time would we, in principle find smaller orbital radii in all things (unaffected by other events) with those of today due to expansion alone?

 

[DrJoePesce]

Yes, we agree on this because endless acceleration in the distant future will not be so kind to things.

But I'm trying to get a feel if there is a consensus with cosmologist as to the expansions effects relative to the other forces. Perhaps this will address my question better...

Is it your opinion that the expansion, say over the last 12 billion years, has separated all objects, even the orbital distance of an electron around a single proton in an isolated patch of space? If we could go back in time would we, in principle find smaller orbital radii in all things (unaffected by other events) with those of today due to expansion alone?

Yes.

Again, the expansion of space on those small scales is miniscule (or even less! ), At the force level the weak and strong nuclear forces dominate and will do so until the far distant future when they are eventually overcome by the stretching of space.

 

[DrJoePesce]

Here on Earth, lodestone, like any magnet, has 2 polarities. Is this because Earth has 2 polarities? Would native lodestone on Jupiter have more than 2 polarities?

Hello Timesemit. Thanks for the question.

Magnets are dipole (having two poles), everywhere, not just because they are on Earth. Jupiter's magnetic field is dipole, so is the Sun's, etc. There are hypothetical objects called magnetic monopoles (having one magnetic pole), but those probably don't exist in nature.

 

[Helio]

Yes.

Again, the expansion of space on those small scales is miniscule (or even less! ), At the force level the weak and strong nuclear forces dominate and will do so until the far distant future when they are eventually overcome by the stretching of space.

Thanks for your response!

I will have to think harder about this. Though locally the expansion is tiny, for a z=10 or so, the expansion since then has been something like 30 fold, so even a tiny electron orbit would have moved outward and should, I think, effect the wavelength of the photon emitted. If so, things like the Balmer series, for instance, will be different today than long ago, perhaps.

 

[DrJoePesce]

Thanks for your response!

I will have to think harder about this. Though locally the expansion is tiny, for a z=10 or so, the expansion since then has been something like 30 fold, so even a tiny electron orbit would have moved outward and should, I think, effect the wavelength of the photon emitted. If so, things like the Balmer series, for instance, will be different today than long ago, perhaps.

I think even over 13.74Billion years the change has not been relevant. Over trillions of years, it will be.

 

[DrJoePesce]

Would you believe our week together is now over? Time does fly, and I've had a blast answering your terrific questions! I'm always heartened to see such enthusiasm about my field, and more importantly, about the universe around us.

Keep thinking big thoughts, keep up the excitement, and keep looking up!

Until next time,

Dr. Joe

 

[Helio]

Best wishes and thanks!

Clear skies!

 

[Wolfshadw]

Thank you Dr. Joe!
I hope we will see you come back soon!

-Wolf sends

 

[togo59]

I am a simple person and this is my first post. In searching these fora, some of the answers I have found to similar questions to this one seem to use obfuscation (at least to me) by twisting all sorts of exotic theories together, which leads to confusion (for me).

My basic observations:
1) It's natural for humans to think in terms of physical things, even if these things could be argued to be properties instead. Perhaps mass is a property and "nothing" is a physical thing. (I don't really care.)
2) We use mathematics to represent (e.g.) quantum, SR and GR. I don't think mathematics is a physical thing (but neither is that existential question my point).

So my question is: What is the most fundamental attribute of a universe? I want to discard notions of "distance", (norms, metrics).

My answer would be "that it is a connected place", in the sense that, ignoring all physical laws, one can define any two distinct points (that could be infinitely close if it were a metric space) such that the two points are (topologically) connected. I.e. I could trace a line from here to the time when the universe was "small" and back out again to any other place, even if a "thing" or information would have to break physical laws to make that journey.

For example, it does not make sense to me that two universes can be connected via a worm-hole. If a photon or a quantum loop could travel from one to another then, in my definition, they are one universe albeit with a weird topology. The other universe might not be physically reachable but it would be communicable: if a "bit" seems to travel from one universe to another, it is in fact travelling from one place to another in the same universe.

The problem with my simplistic notion is that learned and esteemed people commonly talk about multiverses as in the Schrodinger Cat example. To me these are not multiverses they are just bifurcations of one universe.

My view of time is that it is the space in which things can happen. Therefore it doesn't make any sense to talk about "before" time, just as it doesn't make sense to talk about "outside" the universe.

Surely these things are purely logical. If they're correct then one can add more familiar (possibly misleading) notions, like length. Entanglement, for instance, does not need "length". And I love this idea of a modular universe as that might be the answer I'm looking for.

So what is a universe? And why do people keep talking about it (not "them"!) as if they've really seen one?

Roger.