Ask Me Anything AMA with Astrophysicist Dr. Joe Pesce!

[DrJoePesce]

As a fellow ST:TOS fan, I was wondering how you feel about the "remastered"version of episodes vs the originals. Have to say that my favorite episode, "The Doomsday Machine" felt a lot cooler/smoother than the original version.

-Wolf sends

I value the remastered versions of ST:TOS for what they are. They provide a nifty look at digital graphics technology (of the mid 1990s), ultimately "enhancing" the production quality of the television show.

I watch the remastered version, certainly, but I pine for the original. Why? Because the show is a product of the 1960s. Why can't we see it as it was constructed and intended to be? AND the graphics used in the 1960s on ST:TOS were cutting edge - they ARE one of the things that made TOS the jewel that it is (and why it was so remarkable in its day). As I said, the remastered version is an interesting product worth viewing. It's not ST:TOS. So, yes, I feel strongly about this!

But you know what else bothers me? Editing that removed the original (four) commercial breaks. The storyline, the original editing, the soundtrack, were all designed to have these commercial breaks. Removing the original commercial breaks (or, more commonly, adding more), also changes the tone and flow of an original episode.

 

[Helio]

History of all types (and periods) fascinates me. I'm particularly fond of 16th and 17th century England and the Netherlands (and other places too!), where science as we know it today is getting started.

Ah ha. Yes, Huygens did introduce the kind of waves you, no doubt, prefer!

It's quite a story on how light bounced from particle to wave to particle to wave throughout history. I can't imagine, for practical use, much of a particle viewpoint taken in radio astronomy, right?

 

[DrJoePesce]

I would also note this member's question:

@Artistscientist asks:


Wolfshadw
Moderator

A great question that gets to a fundamental of astrophysics. On the local level, the movements of galaxies toward or away from us impart a doppler effect on light emitted from those galaxies (blueshift or redshift). On the larger scale, we have the cosmological redshift which is the stretching of a photon's wavelength as it travels through an expanding universe: the very fabric of the universe is stretching as the photon flies through it, and this increases the wavelength, leading to the cosmological redshift. Redshift is related to distance, and we can measure distances in several independent ways. And when we do, redshift is consistent with the picture I outlined above. There are alternatives, but I am not versed in them, and they haven't yet gained traction.

There is also a thing called gravitational redshift which is caused by photons near an intense gravitational field.

 

[Helio]

On the larger scale, we have the cosmological redshift which is the stretching of a photon's wavelength as it travels through an expanding universe: the very fabric of the universe is stretching as the photon flies through it, and this increases the wavelength, leading to the cosmological redshift.
...
There is also a thing called gravitational redshift which is caused by photons near an intense gravitational field.

Einstein, from what I am trying to understand through some limited reading, had developed his GR theory initially on the equivalence principle. This allowed the then known solar redshifts and the precession of the orbit of Mercury to, finally, be explained. [Luckily, a new, smarter, Vulcan came along once tv was born.]

The solar redshifts, though the data was a bit muddy, became understandable as the solar limb presented, primarily, only the grav. redshift since on the limb the Doppler shifts are not so significant. [This may be one reason he spent more time, apparently, with solar experts than with Hubble when he visited Mt. Wilson, though the solar guys spoke German and he was still learning English at the time.]

But, he recognized he had left out the component involving spacetime effects (I think this is the right term). His starlight near the Sun deflection estimate was the same as the Newtonian deflection in his early model, and the one he expected to get from the German astronomer he helped get funding. [This eclipse expedition to Russia (IIRC) failed as the astronomer was put in a jail as a potential spy, so Einstein was lucky his incomplete theory wasn't falsified, and with some of his own money, apparently. ]

When he realized his shortcoming, he corrected the theory and doubled the deflection amount, which was confirmed by Eddington and Dyson (late 1919). [The better data came from Dyson's team, actually.]

So, my question is whether their is some relationship between the spacetime deflection factor (Einstein's second key element in GR) and the cosmological redshift? [I have struggled trying to see how feeble spacetime in empty space can suck so much energy from an EM particle given that feeble gravity for galaxies holds-up so well against the expansion.]

 

[DrJoePesce]

Einstein, from what I am trying to understand through some limited reading, had developed his GR theory initially on the equivalence principle. This allowed the then known solar redshifts and the precession of the orbit of Mercury to, finally, be explained. [Luckily, a new, smarter, Vulcan came along once tv was born.]

The solar redshifts, though the data was a bit muddy, became understandable as the solar limb presented, primarily, only the grav. redshift since on the limb the Doppler shifts are not so significant. [This may be one reason he spent more time, apparently, with solar experts than with Hubble when he visited Mt. Wilson, though the solar guys spoke German and he was still learning English at the time.]

But, he recognized he had left out the component involving spacetime effects (I think this is the right term). His starlight near the Sun deflection estimate was the same as the Newtonian deflection in his early model, and the one he expected to get from the German astronomer he helped get funding. [This eclipse expedition to Russia (IIRC) failed as the astronomer was put in a jail as a potential spy, so Einstein was lucky his incomplete theory wasn't falsified, and with some of his own money, apparently. ]

When he realized his shortcoming, he corrected the theory and doubled the deflection amount, which was confirmed by Eddington and Dyson (late 1919). [The better data came from Dyson's team, actually.]

So, my question is whether their is some relationship between the spacetime deflection factor (Einstein's second key element in GR) and the cosmological redshift? [I have struggled trying to see how feeble spacetime in empty space can suck so much energy from an EM particle given that feeble gravity for galaxies holds-up so well against the expansion.]

This is a great question that really gets to the heart of the vastness of space, beyond human comprehension really. The photons are traveling through vast amounts of space, and, as they fly, the space they are traveling through is being stretched.

 

[DrJoePesce]

I don't want to pose a question that can't be answered, but I have wondered for a long time whether or not our universe is everything in existence, including all the dimensions we have yet to discover. If this is true, I don't see the universe simply reversing course because it apparently is still accelerating. What I see is a space-time fabric possibly being stretched to its limits before quantum leaping into something with different properties and different laws of physics. From there, it may undergo more quantum leaps before reverting back to whatever it was before the Big Bang.

If the universe is only a fraction of everything in existence, it becomes a much more complicated picture, perhaps beyond the reach of the most intelligent beings to have ever existed. I realize there is a 0.0000000000001% chance we are the only intelligent beings to ever exist in the universe.

Oh, I loved you in "My Cousin Vinny." Just kidding. His surname is Pesci.

Cosmology is so thought-provoking, isn't it? The universe is everything in existence we can know about. There are some thoughts of multi-verses, and the like. But, for the most part, these views (maybe we can call them models) cannot be tested, and so are not scientific and merely speculation. That doesn't mean 1) we won't be able to conduct tests in the future and 2) there won't be new and wonderful models.

As to your point about the universe reversing: Up until the discovery of dark energy, the big open question was did the universe have enough mass (or mass density) to slow the universal expansion, and indeed even reverse it so that eventually the universe would collapse? The view was that the mass density of the universe was not sufficient to reverse the expansion, but it would slow it down. So, a universe expanding forever but at an ever-decreasing rate. Dark energy basically throws all that out, because not only is there not enough matter to stop the expansion, but the expansion rate is accelerating. It looks like the universe will expand forever.

P.S. I love "My Cousin Vinny" too!

 

[Helio]

The photons are traveling through vast amounts of space, and, as they fly, the space they are traveling through is being stretched.

Right, but I will assume you see where I have trouble with, say, a 12 billion-year old galaxy constantly being stretched yet never fully allowing the expansion to get the best of it, thanks to its self-gravity that overpowers that expansion.

Yet, if we know gravity is extremely weak relative to EMf, you can see my puzzlement in trying to see how the extremely strong (EMf) allows the expansion to stretch that which gravity seems to disallow. Perhaps you can suggest what I'm missing.

 

[rabsal]

Yes, the mass of the collapsing star (primarily) will lead to the complete collapse to a singularity. I'm not sure how a black hole can collapse further/again, as the singularity is the ultimate collapsed object.

We didn't know they would radiate energy outwards either but they do, and I want to try and prove that BH's have a "density maximum" and this relates to the space itself as "giving way" in whatever way it can, which would be from one of the space density constants being bent or broken...but I am just an undergraduate and haven't gotten to the details yet, so check back in a few years....
But if inflation occurred a BH going expansive could explain it...in my visible universe...

 

[rabsal]

Right, but I will assume you see where I have trouble with, say, a 12 billion-year old galaxy constantly being stretched yet never fully allowing the expansion to get the best of it, thanks to its self-gravity that overpowers that expansion.

Yet, if we know gravity is extremely weak relative to EMf, you can see my puzzlement in trying to see how the extremely strong (EMf) allows the expansion to stretch that which gravity seems to disallow. Perhaps you can suggest what I'm missing.

That's the dark matter that seems to keep galaxies together and not fly apart but what is dark matter?...it could be a phase shift of dark energy that gathers around massive spinning objects or some form of quantum drag...dark energy is pushing the expansion not EM....we'll see what Joe says..

 

[JSNardello]

Hi Joe
Black holes can hold entire galaxies in form and the speed of gravity is roughly as fast as the speed of electromagnetic waves squared. So could gravity, as one of the four forces in our standard model of particle physics be limited to our universe?

Dr. Joe P.,
This is more fun than a barrel of monkeys.
When electromagnetism and gravity are combined into a single framework, can we solve the mystery of the most prevalent force with Gravity equals Mass times Speed of electromagnetic waves squared?

 

[DrJoePesce]

Right, but I will assume you see where I have trouble with, say, a 12 billion-year old galaxy constantly being stretched yet never fully allowing the expansion to get the best of it, thanks to its self-gravity that overpowers that expansion.

Yet, if we know gravity is extremely weak relative to EMf, you can see my puzzlement in trying to see how the extremely strong (EMf) allows the expansion to stretch that which gravity seems to disallow. Perhaps you can suggest what I'm missing.

A terrific question, Helio, and it's one where that vastness of space gets us.

Currently, the universal expansion is on a very large scale. The expansion rate, Hubble's constant, is still being pinned down, but let's say it's 67 km/s/Mpc. That is, the expansion rate is 67 km/s BUT over 3.3 million light years. I will leave it as an exercise to determine the expansion rate on a human or galactic scale. The universe is expanding on a human scale, just at a miniscule rate. I started by saying "currently". In the far distant future, expansion becomes relevant even on the small scale, and eventually atomic nuclei will be pulled apart from their electrons, subatomic particles will be pulled apart, etc.

As for relative strengths of the forces: the difference between gravity and the other three fundamental forces is that gravity operates on the very large scales while the other three - though tremendously stronger than gravity - only operate on a very small (atomic or sub-atomic) scale.

 

[DrJoePesce]

We didn't know they would radiate energy outwards either but they do, and I want to try and prove that BH's have a "density maximum" and this relates to the space itself as "giving way" in whatever way it can, which would be from one of the space density constants being bent or broken...but I am just an undergraduate and haven't gotten to the details yet, so check back in a few years....
But if inflation occurred a BH going expansive could explain it...in my visible universe...

Thanks for the input! By "radiate energy outwards" you are referring to Hawking radiation, I assume. Black holes can indeed lose mass through this process (basically two conjoined or entangled particles are near a black hole's event horizon, one falls into the black hole and the other escapes, taking energy/mass with it). But the mass-loss rate is incredibly slow. Given long enough, the black hole will lose all its mass. It won't explode, however, it will just disappear.

 

[DrJoePesce]

That's the dark matter that seems to keep galaxies together and not fly apart but what is dark matter?...it could be a phase shift of dark energy that gathers around massive spinning objects or some form of quantum drag...dark energy is pushing the expansion not EM....we'll see what Joe says..

A key question of modern astrophysics! We don't yet know what dark matter is. The current candidate is some type of sub-atomic particle. It could, indeed, be something else.

 

[David-J-Franks]

Was excited to see you back Dr. Joe

I learnt from reading these forums that the speed of light has only been measured with a two-way trip ie it's always been reflected back from something. The reason given why a 1-way speed measurement cannot be made is that it is not possible to synchronise 2 clocks because when you move them apart special relativity says they will alter. I don't like it when someone says you can't do something so I came up with a thought experiment to overcome the synchronising clock problem. I'm sure it must be wrong because I'm not a scientist, so I would like to see what you think

If you take a clock with the dial on and then have a very long shaft with a similaur dial on the other end will that mean the two ends of the shaft are synchronised in time? So, therefore can you measure the one-way speed of light? Basically it is the same clock that both observers at each end are referring to. For the sake of symmetry you could even have the clock mechanism in the middle and a shaft going in each direction.

This need not be a thought experiment, in space it would theoretically be practical to have say a 10 km or even 100 km a long shaft so both ends would therefore be exactly synchronised in time, so you could perform lots of experiments with it. Obviously, you could replace the dial with some electrical triggers and make it digital.

Also you could have one end of the shaft nearer a strong gravitational body where time is supposed to slow down so what happens to the other end of the shaft?

Yet again you could also spin one end of the shaft round the other and the different velocities again should produce the different times, so what happens to each end of the shaft in that case?

I can't get my head around this, so your help would be very much appreciated

Thank you

 

[Helio]

Currently, the universal expansion is on a very large scale. The expansion rate, Hubble's constant, is still being pinned down, but let's say it's 67 km/s/Mpc. That is, the expansion rate is 67 km/s BUT over 3.3 million light years.

Assuming you meant 3.3 billion lyrs., is that our current SN study limit? Will we be bumping that distance soon, perhaps with the GMT or the Webb spacescope?

I will leave it as an exercise to determine the expansion rate on a human or galactic scale. The universe is expanding on a human scale, just at a miniscule rate.

Doesn't gravity easily allow things like planets to keep following Kepler's laws regardless if a little bit of space slowly oozes in between them? I don't see gravity being bothered much by expansion on any local basis, perhaps not even within galactic clusters. Is this the proper view of expansion effects?

 

[DrJoePesce]

Was excited to see you back Dr. Joe

I learnt from reading these forums that the speed of light has only been measured with a two-way trip ie it's always been reflected back from something. The reason given why a 1-way speed measurement cannot be made is that it is not possible to synchronise 2 clocks because when you move them apart special relativity says they will alter. I don't like it when someone says you can't do something so I came up with a thought experiment to overcome the synchronising clock problem. I'm sure it must be wrong because I'm not a scientist, so I would like to see what you think

If you take a clock with the dial on and then have a very long shaft with a similaur dial on the other end will that mean the two ends of the shaft are synchronised in time? So, therefore can you measure the one-way speed of light? Basically it is the same clock that both observers at each end are referring to. For the sake of symmetry you could even have the clock mechanism in the middle and a shaft going in each direction.

This need not be a thought experiment, in space it would theoretically be practical to have say a 10 km or even 100 km a long shaft so both ends would therefore be exactly synchronised in time, so you could perform lots of experiments with it. Obviously, you could replace the dial with some electrical triggers and make it digital.

Also you could have one end of the shaft nearer a strong gravitational body where time is supposed to slow down so what happens to the other end of the shaft?

Yet again you could also spin one end of the shaft round the other and the different velocities again should produce the different times, so what happens to each end of the shaft in that case?

I can't get my head around this, so your help would be very much appreciated

Thank you

Thank you David-J-Franks! Fascinating question and topic! I REALLY like that you are thinking about this and creating experiments! I will have to think more about your experiments but let me offer the following in the meantime.

Not all measurements are necessarily two-way. In the astronomical case, if we know distances to an astronomical object and we see something emitting light (for example, a blob in an accretion disk, and then reflection of that emitted light off something local to the source) we can measure the speed of light. (And/or we can measure distances at the local source given the speed of light.)

But we can also do this in the laboratory, creating a photon and then detecting it, and thus measuring the speed of light.

You also allude to relativity and changing clock speed in the presence/absence of a gravitational field. This has been measured astronomically, but also locally: Something that we use every day - GPS - must include a relativistic time-correction because the GPS satellites are in Earth orbit, but we are on the surface and there's a difference between our respective clocks. This has been measured in the laboratory too, given the incredibly accurate clocks we can produce.

 

[DrJoePesce]

Assuming you meant 3.3 billion lyrs., is that our current SN study limit? Will we be bumping that distance soon, perhaps with the GMT or the Webb spacescope?

Doesn't gravity easily allow things like planets to keep following Kepler's laws regardless if a little bit of space slowly oozes in between them? I don't see gravity being bothered much by expansion on any local basis, perhaps not even within galactic clusters. Is this the proper view of expansion effects?

Hello Helio! Thanks for the follow up. No, I meant million (I was converting megaparsecs into light years). That is, the expansion rate is "only" 67 km per second over a distance of 1 megaparsec (put another way, for every 1 megaparsec, the universe expands by 67 km per second). That's quite a small expansion rate, and it becomes even smaller when you get to the human scale.

. Again, as above, on the scale of a planet and its star the expansion rate is miniscule. But over time, and eventually (assuming something else hasn't happened in the meantime), the distance between the star and its planet will become so large that gravity won't be able to keep the system bound.

Of course, a planet will keep orbiting a star following Kepler's laws, but things change as the distance between the planet and its star increases (due to expansion), orbital velocity, for example.

Again, as above, on the scale of a planet and its star the expansion rate is miniscule. But over time, and eventually (assuming something else hasn't happened in the meantime), the distance between the star and its planet will become so large that gravity won't be able to keep the system bound.

 

[DrJoePesce]

Thanks, Helio - it's good to be back!

Yeah, isn't this fascinating? Our estimates are going to change as our technology improves and we make new discoveries. I think that's a pretty good number! We are still trying to understand these early galaxies, but I think they are smallish. I'm not sure what an average number of stars is, but probably in the millions.

On the other hand, I'm intrigued by the recent discoveries of galaxies larger than expected early in the universe. See, for example, this based on ALMA observations:

https://www.space.com/old-galaxy-in-early-universe-aless0731

And the James Webb Space Telescope will tell us more!

By the way, speaking of the early universe, first galaxies, the first stars, and us, you might enjoy this video:

View: https://www.youtube.com/watch?v=hFULDp3QHVQ

 

[Helio]

Hello Helio! Thanks for the follow up. No, I meant million (I was converting megaparsecs into light years). That is, the expansion rate is "only" 67 km per second over a distance of 1 megaparsec (put another way, for every 1 megaparsec, the universe expands by 67 km per second).

Eek, I should've seen that.

Of course, a planet will keep orbiting a star following Kepler's laws, but things change as the distance between the planet and its star increases (due to expansion), orbital velocity, for example.

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?

Again, as above, on the scale of a planet and its star the expansion rate is miniscule. But over time, and eventually (assuming something else hasn't happened in the meantime), the distance between the star and its planet will become so large that gravity won't be able to keep the system bound.

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?

 

[Helio]

By the way, speaking of the early universe, first galaxies, the first stars, and us, you might enjoy this video:

View: https://www.youtube.com/watch?v=hFULDp3QHVQ

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.]

 

[Kriscateau]

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.]

 

[IG2007]

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.

 

[Amansingh11789]

Hey Astronomy Fans!

I’m happy to be here again on this AMA! Your questions and enthusiasm are great, and I look forward to hanging out with you this week.

To recap my background: I'm an astrophysicist primarily interested in the environments of the galaxies hosting supermassive black holes (also known as Active Galactic Nuclei). I've worked with clusters of galaxies, and the atmospheres of giant and supergiant stars. Currently I'm a Program Director at the National Science Foundation (NSF), Division of Astronomical Sciences, responsible for the National Radio Astronomy Observatory (NRAO); a part-time Professor at George Mason University in Fairfax, Virginia; and a Visiting Professor at the University of Colorado, Boulder, Colorado. And I'm a Fellow of the Royal Astronomical Society. Oh - and I LOVE all things Star Trek!!

My knowledge base is broad, but I know most about the areas I mentioned above so might have to do some research to find the answer to areas outside my day-to-day experience. Please be patient with me - the universe is enormous!

Also, there may be lots of questions I can’t answer because I don’t know – and maybe the answer isn’t yet known (that’s a fun part about astronomy – lots of unknowns still). Please keep this in mind. I will try to answer as many questions as possible.

Astronomy continues to surprise and inspire. Thank you for letting me share it with all of you!

Dr Joe

Dr joe ,
So glad to find someone who has such vast knowledge about our space and believes in new possibilities of new discoveries . Recently I started a research about gravity and i believe I figured out the simplest way to explain it . All the space community have been trying to figure out what exactly gravity is which is always quoted as either imaginary force or impossible to explain kind of force. I believe it’s easy to explain if we try to look at it with a different perspective. Recently there was a news about space beyond our solar system not being empty that made me think that maybe the vacuum present in our solar system is the answer to gravity . Our planets are spinning at a very high speed smaller as earth or Mars and bigger as Jupiter or Saturn is it possible that they are acting as vacuum cleaners . Surface of all the planets is rough and hence creating an effect of blades of a vacuum turbine . All the suction created by the planets left our solar system empty and all the planets are covered with high dense gasses . Gravitation between planets and sun could be explained by the theory of galactic drift . Maybe the planets are not rotating around the sun but traveling all together seem to portray an orbital arrangement like pallets of a shotgun. Gravity might not be a force but rather a combination of phenomenas gravity on earth could just be high pressure created by the gases around us by creating a medium in which we can move easily but it’s hard to escape it . To escape it might be easier to instead push through it but by creating a hole . By hole I mean a vortex . There are so many questions and potential findings that could be achieved by these observations but I need to understand if I am not wrong about all this.

 

[jimocz]

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?

 

[JSNardello]

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?