Can gravity exist without mass?

[pmb_phy]

Why do you say this?

As matter falls into a black hole it slows down and, as measured by an outside observer, never gets to or past the event horizon.

Can you give a referenece?

I'll look for one. Perhaps I'm wrong.

Pete

 

[George Jones]

As matter falls into a black hole it slows down and, as measured by an outside observer, never gets to or past the event horizon.

It seems that you mean the purely classical case of stellar collapse. I thought you meant either the semi-classical case of Hawking radiation, something completely non-classical like loop quantum gravity or string theory.

In the classical case, the existence of an infinite redshift surface does not preclude the existence of spacetime singularities. In fact, in the purely classical case of stellar collapse, once the collapse proceeds far enough (as it does for sufficiently massive stars), I know of no way to evade the Penrose-Hawking singularity theorems. A person falling along with the collapsing surface of the star will rapidly find himself inside an event horizon, and will almost as rapidly himself up close and personal with a singularity.

If Hawking radiation is considered, the mainstream view is that a singularity still forms. A small minority of physicists think that Hawking radiation will carry away enough mass/energy to prevent the formation of an event horizon and singularity; see https://www.physicsforums.com/showthread.php?p=1534827#post1534827".

Quantum theories of gravity are not sufficient developed for the emergence of a consensus view on status of spacetime singularities inside event horizons.

 

[pmb_phy]

It seems that you mean the purely classical case of stellar collapse.

The term classical includes relativistic. If you mean Newtonian then no, the slowing down of matter and stopping outside the event horizon is not a Newtonian phenomena.

In the classical case, the existence of an infinite redshift surface does not preclude the existence of spacetime singularities.

True.

In fact, in the purely classical case of stellar collapse, once the collapse proceeds far enough (as it does for sufficiently massive stars), I know of no way to evade the Penrose-Hawking singularity theorems.

Sorry but I never heard of them. But this is an observer dependant phenomena. Whether something crosses the event horizon depends on who is doing the observing.

A person falling along with the collapsing surface of the star will rapidly find himself inside an event horizon, and will almost as rapidly himself up close and personal with a singularity.

True. But the subject is in regards to observers outside the event horizon. Not about observers who are falling through it.

Pete

 

[MeJennifer]

Note that black holes can only completely form in an open universe.

 

[Haelfix]

Thats a bit dubious MeJennifer. I know why you would say that, but I think its a bit of a mathematical technicality more so than a real physical effect. In physics, we tend to cut infinities off as a general rule.

A big star collapses, it pops out a black hole. Which is why we likely had black holes 10 billion years ago, even though we weren't sure whether or not we were open, closed or critical. Indeed, they may have evaporated already, depending on how you model quantum effects.

 

[George Jones]

The term classical includes relativistic.

Yes, usually, and that is how I used the term

Sorry but I never heard of them. But this is an observer dependant phenomena. Whether something crosses the event horizon depends on who is doing the observing.

The Penrose-Hawking singularity theorems are infamous in general relativity. Misner, Thorne, and Wheeler gives a brief treatment, Wald's text gives a detailed treatment, and they are at least mentioned in many introductory GR texts.

True. But the subject is in regards to observers outside the event horizon. Not about observers who are falling through it.

No, the subject is singularities inside black holes.

In post #48, you said

A star collapsing might collapse into a black hole and yet leave no singularity.

In classical general relativity, this just isn't true.

 

[pmb_phy]

The Penrose-Hawking singularity theorems are infamous in general relativity. Misner, Thorne, and Wheeler gives a brief treatment, Wald's text gives a detailed treatment, and they are at least mentioned in many introductory GR texts.

Do you have a precise reference?

Pete

 

[George Jones]

Do you have a precise reference?

I won't have the same spacetime coordinates as my relativity books until Monday, and I can give you a bunch of references then.

The only reference that I have at home is The Edge of Infinity: Beyond the Black Hole, by Paul Davies, which has a very good popular-level treatment of singularities. I really like this book, and it gives a tremendous (and quite accurate) explanation of Penrose's first singularity theorem. I even recommend it as a complement to mathematical references for physics types encountering for the first time the technical details of singularity theorems.

 

[pmb_phy]

I won't have the same spacetime coordinates as my relativity books until Monday, and I can give you a bunch of references then.

The only reference that I have at home is The Edge of Infinity: Beyond the Black Hole, by Paul Davies, which has a very good popular-level treatment of singularities. I really like this book, and it gives a tremendous (and quite accurate) explanation of Penrose's first singularity theorem. I even recommend it as a complement to mathematical references for physics types encountering for the first time the technical details of singularity theorems.

Great! Thanks George! A short time back I got into a discussion about black hole singularities and I became convinced that it wasn't possible to state that a black hole had a singularity since there would be no way to observe them. I also read something in Kop Thorne's book "Black Holes & Time Warps" regarding frozen stars. I guess I gave up too soon and for no good reason. Thanks for catching me on this. Greatly appreciated.

Pete

 

[quantumcore]

well empty space does not mean that there is zero energy , and as relativity says energy is equivalent to mass , and mass create gravity . hence if space -time is there then i think gravity is also there.

 

[NYSportsguy]

well empty space does not mean that there is zero energy , and as relativity says energy is equivalent to mass , and mass create gravity . hence if space -time is there then i think gravity is also there.

Quantumcore pretty much hit it on the head. If you think about it are there stars that lay just by themselves in the universe? Most, if not all stars I believe tend to be in clusters around galaxies. The super massive black hole in the center of these (all the galaxies) of the universe cause this. It is the super dense state of these black holes that cause the the starts to be somewhat revolving around them (what we know as gravity) in a galaxy like state to begin with.

If you still don't believe me...just ask Einstein.

 

[HitchHiked]

It is the super dense state of these black holes that cause the the starts to be somewhat revolving around them (what we know as gravity) in a galaxy like state to begin with.

That's a massive span of energy from "mass", emanating from the super massive black hole (at center of galaxy) all the way out to the most distant stars, and steering them around the galactic center. And why are they planar and not symmetrical spheroid?

Is there still "mass" present at these outer points, where gravity is obviously moving these stars? The argument (I guess) is that there's a field present but from it's origin, many light years away.

 

[Naty1]

Does gravity exist if the universe is devoid of all matter, including the dark-matter?

well empty space does not mean that there is zero energy , and as relativity says energy is equivalent to mass , and mass create gravity . hence if space -time is there then i think gravity is also there.

is one view which makes sense.

The relates to when pressure and energy appeared in the universe with a gravitational field:

From Fabric of the Cosmos, Brian Greene:

how does gravity emerge from various initial conditions, big bang ...from grand unification conditions...Higgs fields appear during spontaneous symmetry breaking and give rise to mass...Above 10^28 degrees the other three forces were unified...

So it sounds like sometime before 10^-12 and slightly after t=0 seconds gravity existed without mass...and I guess that might vary depending on which model is used...

 

[chis]

The simple answer is no. Without mass nothing exists, most importantly perception. Move away from a body of mass/perception and your perception decreases slightly. Astronaughts experience this reduction in perception through altered taste and spatial perception reduction. Trouble with docking and a strange taste reaction to favorite foods are examples. Over large tracts of reduced mass or empty space light is the only dimention that we can percive truly.
With no mass gravity would be infinite and pure, but there would be no one able to percive it.

 

[TheJackel]

I'm curious, I've been doing a lot of reading about Quantum Electrodynamic physics.. Under this theory it asserts that only on average that there is nothing to where energy is borrowed from the future with the stipulation that it must quickly be returned.. This being the process of particle and anti-particle emergence and collisions to where they quickly destroy each other.

Now I have a problem with the term nothing in understanding how this could be possible to exist. Because I see this as claiming that a -1 energy or -1 spatial dimension would some how be capable of existing. So I am wondering if anyone has considered that the Universal set is energy itself to where all of existence is entirely comprised of energy..

So is nothing really a no-thing or zero base energy that can't be measured because it's the base minimum to all existence? So on an energy scale there would be no literal zero energy but a zero base energy that vibrates or self-osculates to drive emergence vs borrowing energy from the future.. Hence, a representation of (0,1) to where it's only perceived to be nothing, but in reality it really isn't nothing but no-mass energy at it's lowest possible energy level or complexity..

This is where 0 = no other objects or levels of energy above zero base energy at any given focal point regardless if there is an infinite number of neighboring 0's.. And this is where 1= the base energy or the only object at any given focal point regardless if there are an infinite number of other neighboring 1's.. Can this be represented similar to Qbits in concept?

And sorry if this seems like a dumb question because I'm not a physics major.. I am just curious..

 

[astronomer121]

Hope this will help u http://gravity-nirmal.blogspot.com