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Rethinking the origins of the universe

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Re: Rethinking the origins of the universe

#31

Post by sampo »

phkahler wrote: post #18

Now that all the physicists are reading, I have a question: Are the trajectories of light beams following the curvature of space-time reversible? In other words, if I reflect a light beam back on itself, does it return to its source? Because if that's true (and my feeble understanding is that it is true), then light can't enter a black hole or the reverse path would allow light to escape. What am I missing here?

I think, even if light beam trajectories were reversible (to which I cannot answer) in normal space, the singularity breaks the rules of the normal space.

Re: Rethinking the origins of the universe

#32

Post by StefanKarpinski »

This paper claims that black holes can't come into existence, which is subtly different from claiming that they cannot exist. In particular, black holes can exist as long as they've always existed – it's just that new ones can't come into existence. Maybe the universe just has a fixed number of singularities. [I am not a physicist – this just struck me as an inaccurate implication in the article.]

Re: Rethinking the origins of the universe

#33

Post by trhway »

Ok. To start she addresses only "Gravitationally Collapsing Star"s. Interesting result, may be many star lifecycles don't end in a black hole. The "before-black-hole" state she describes still would involve significant time dilation and thus what we see as Hawking radiation from black hole may just be Hawking radiation from "before-black-hole" star. Looks the same :)

The result doesn't say that black hole is impossible. It says that a star's collapse loses mass faster than acceptable for the collapse to end in black hole.

Some misconceptions in the web-post:

>They are the ultimate unknown – the blackest and most dense objects in the universe that do not even let light escape.

a black hole isn't necessary most dense. After all a black hole with a mass of visible Universe would be only 125 times denser than current average density of the visible Universe (i.e. 45B light years radius of visible Universe have 10B light years Schwarzschild radius)

> So the story went, an invisible membrane known as the event horizon surrounds the singularity and crossing this horizon means that you could never cross back. It’s the point where a black hole’s gravitational pull is so strong that nothing can escape it.

"membrane" is very bad illustration. It is constantly changing solution to the gravitational equations. One moment it is here, another moment - it has moved because gravitation of black hole changes and a lot of oscillations/perturbations happen. One moment you're inside, another - outside.

"gravitational pull is so strong that nothing can escape it" - that's bad wording too. It is actually "gravitational well is so deep that nothing can escape it". Feel the difference :) A huge black hole may have pretty weak gravitation at its horizon.

Thus no-escape is valid only in the sense that escaping object just would never reach "a point at infinity" from the black hole and the light would get red-shifted into full oblivion.

Re: Rethinking the origins of the universe

#34

Post by tericho »

danbruc wrote: post #8

Well, there is are a lot of observational evidence for black holes - the by far most likely scenario is that the model they analyzed does not describe the physics of black holes in our universe.

This is the first question I thought of. I'm not a physicist so I dare say I can't interpret the paper but I'm curious how she explains the seemingly observed orbits of stars around the black hole in the middle of our galaxy and others[1][2].

[1]http://astro.uchicago.edu/cosmus/projects/UCLA_GCG/ [2]http://en.wikipedia.org/wiki/Accretion_disc

Re: Rethinking the origins of the universe

#35

Post by sampo »

Stwerp wrote: post #6
chc wrote: post #3

Given how important this would be, it seems a bit odd that she just threw it on ArXiv rather than having it peer-reviewed. Also, the press release's explanation of what Hawking radiation is sounds strange to me, though I'm not an astrophysicist. It all makes me very hesitant to put any stock in this right now (well, at least it in meaning what's suggested here).

I understood that it was common to post the paper to arxiv when it was in the process of being peer reviewed by a journal. The problem is the extended lag time between submission and final publication with most journals which pre-print archives like arxiv try to solve. Do people really just "submit to arxiv" and then that it? I didn't know that, but its not common in my field to use arxiv so I have not kept up with a…

> Do people really just "submit to arxiv" and then that it?

Some people do: http://en.wikipedia.org/wiki/Grigori_Perelman

Re: Rethinking the origins of the universe

#36

Post by faizshah »

I'm not at all acquainted with astrophysics but I remember seeing an article state that there was a different physicist who proved this same thing:

https://news.ycombinator.com/item?id=7191324

A quick google shows his response to this:

https://twitter.com/abhasmitra/status/514804101024997376

His response:

"Hawking radiation is unproven. And particle physicists are not aware that even without any Quantum Mechanics, classical gravitation dictates that all gravitational collapse must be accompanied by radiation. :

http://link.aps.org/doi/10.1103/PhysRevD.74.024010

(http://arxiv.org/pdf/gr-qc/0605066v3.pdf)

And then grav collapse should naturally lead to radiation supported ECO: http://www.sciencedirect.com/science/article/pii/S1384107606...

http://mnras.oxfordjournals.org/content/369/1/492

http://mnrasl.oxfordjournals.org/content/404/1/L50

And as far as non -formation of ``Event Horizon'' is concerned, in contrast to the conjectures of the present yet unpublished paper I gave EXACT proof:

http://www.ias.ac.in/pramana/v73/p615/fulltext.pdf

But phys.org never highlighted my research which is infinitely more accurate than the present paper whose authors are not even aware that Question of Hawking Radiation Would Arise Only If There Would Already Be a Black Hole With an Event Horizon. Therefore This paper is not self-consistent. But that does not matter:

The lead author of this paper has CAMBRIDGE AFFILIATION.

So phys.org is glad to highlight an inconsistent and yet unpublished paper by ignoring my series of my exact and original papers on the same topic."

I don't have any background in astrophysics, can anyone comment on Dr. Mitra's response and the relation of his work to the above research?

The best discussion I can find on Dr. Mitra's work is on quora: https://www.quora.com/Is-it-true-that-Abhas-Mitra-resolved-t...

Re: Rethinking the origins of the universe

#37

Post by lutusp »

phkahler wrote: post #18

Now that all the physicists are reading, I have a question: Are the trajectories of light beams following the curvature of space-time reversible? In other words, if I reflect a light beam back on itself, does it return to its source? Because if that's true (and my feeble understanding is that it is true), then light can't enter a black hole or the reverse path would allow light to escape. What am I missing here?

> Are the trajectories of light beams following the curvature of space-time reversible? In other words, if I reflect a light beam back on itself, does it return to its source?

Yes, it would, assuming you have a way to reflect a beam back the way it came, like the kind of retro-reflectors the Apollo astronauts left on the moon. If you were an observer and saw a laser beam emanating from some distant place, and you wanted to assure that your laser beam would be most likely to be seen there, you would point it at the exact opposite heading -- assuming neither the source nor destination were in motion.

> Because if that's true (and my feeble understanding is that it is true), then light can't enter a black hole or the reverse path would allow light to escape.

That's a different question with a different answer. If you point a laser beam at a surface that absorbs most or all the radiation that falls on it, it's possible that none of the initial radiation will be returned to the source. But -- very important -- all the energy is accounted for. If the initial light beam has energy E, then the energy absorbed and reflected by the target will also equal E, not necessarily the same wavelengths but the same total energy. This applies to black holes as well -- they conserve energy.

Re: Rethinking the origins of the universe

#38

Post by Ynought »

phkahler wrote: post #18

Now that all the physicists are reading, I have a question: Are the trajectories of light beams following the curvature of space-time reversible? In other words, if I reflect a light beam back on itself, does it return to its source? Because if that's true (and my feeble understanding is that it is true), then light can't enter a black hole or the reverse path would allow light to escape. What am I missing here?

Yes, to the best of my knowledge, in general light beams following the curvature of space-time are reversible so that you would be correct for everything EXCEPT for the special case of black holes.

In the case of black holes, the escape velocity of the black hole is simply too great to allow light to escape at it's velocity if it originates from within the event horizon.

It would be like if you were rolling tennis balls to a friend across a trampoline. If you place a bowling ball in the middle of the trampoline, suddenly rolling the balls straight to your friend won't work anymore, because you need to roll them angled to account for the bowling ball in the middle of the trampoline causing the trampoline to be bent a bit so the balls will curve around the bowling ball and a person on the other side of the trampoline can then grab them and roll them back to you with the exact same speed and angle that you rolled them to that person.

However, if you tried to roll a tennis ball instead from the MIDDLE of the trampoline (where the bowling ball is) to your friend you would find that no matter what angle you chose you could not get the tennis ball out if you used the same speed to roll it as before. On the other hand, your friend will of course have no problem rolling tennis balls from the side of the trampoline inward to you.

This is the situation you find light in. Because the absolute maximum velocity that ANYTHING including light can have in a vacuum is equal to c if the black hole is bending the trampoline of space time so much that that velocity doesn't surpass the curvature then it doesn't matter what angle the light faces, it's just going to end up heading right back towards the black hole.

Re: Rethinking the origins of the universe

#40

Post by darkmighty »

trhway wrote: post #33

Ok. To start she addresses only "Gravitationally Collapsing Star"s. Interesting result, may be many star lifecycles don't end in a black hole. The "before-black-hole" state she describes still would involve significant time dilation and thus what we see as Hawking radiation from black hole may just be Hawking radiation from "before-black-hole" star. Looks the same :) The result doesn't say that black hole is impossib…

You seem to be knowledgeable, so is there a plausible bridge between the impossibility of this kind of collapse and complete impossibility of black holes?

I mean, what if could construct a collapse to your desire, e.g. smashing dense cold chunks, would those necessarily radiate enough energy to prevent collapse too?

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