# Thoughts on blackholes

1. Oct 31, 2006

### meph

If blackholes are at the centre of each galaxy is it possible that all the matter from that paricular galaxy came from another universe through the blackhole sucking in one side and blowing out the other?

Transfering matter from one universe to the other.

Perhaps this a natural way to move matter from one universe to another.

2. Oct 31, 2006

### Nexus555

While I do not think that is what most scienctist think today, I have ponder this myself. I've thought of either a transfer of matter to a different universe, or perhaps the creation of a new universe. Since there is a singularity in a black holes, maybe it causes it's own "big bang" and begins a whole new universe.

We may think of the new universe as small in scale, however size is relative in my opinion. If there are other universes, ours might be a pea compared to some others.

However my beliefs and what you have stated are not currently accepted. However I feel we really do not know at this point.

3. Oct 31, 2006

### SpaceTiger

Staff Emeritus
I'm not a GR expert, but I think a primordial rotating (Kerr) black hole can connect to another "universe", but can't expel matter from it; i.e. nothing can come out from the event horizon. The black holes at the centers of galaxies are probably not primordial, however (they likely came from collapsed stars), so it's not clear whether or not they can connect to other universes.

4. Oct 31, 2006

### sardar

Your assumption can be true if we take Conservation of matter(energy) as an infallible law of the Universe, then offcourse we can postulate the existence of so called Whiteholes( speculated by Hawking) and we can say that if matter is going out then it must be coming in also from some other universe. But then there is a glitch here, that all physical laws break down at singularity of a black hole, so asking the question of the validity of conservation of energy or matter would be futile and hence we are not even allowed to ask questions at the singularity, that is what my view is.

5. Oct 31, 2006

### Phobos

Staff Emeritus
Welcome to PF!

Black holes are not necessarily at the center of EACH galaxy, although it seems that "supermassive black holes" may be present in the centers of large galaxies.

As previously noted, matter cannot escape the event horizon of a black hole, so the matter from galaxies did not originate from their central black holes.

The current cosmological model does not include "another universe". (although things like String Theory may get into that concept)

The current model is that galaxies formed from matter created as a result of the Big Bang in this universe. There is, however, an ongoing debate as to whether the supermassive black holes in the centers of large galaxies formed after the galaxy did or if they were the "seed" that matter gathered around to form the galaxy.

6. Nov 1, 2006

### Chronos

The 'other universe' postulate solves nothing [where did it all come from], it merely evades the question. I think science demands we place observational limits on the rules of evidence . . . [if you don't see it, it ain't there].

7. Nov 1, 2006

### Nexus555

That's not true, it neither does or does not solve anything. And most likely, we will not be able to observe this due to the event horizion. Therefore it's a futile speculation in either case.

And like I said about the "other universe," why couldn't blackholes actually create another universe? A singularity sounds a lot like our universes (big bang?).

I do have a question though. I know how blackholes eventually dissipate (hawkings radiation, etc.) But once a blackhole has finially diminished, what happens to the information in the former event horizion?

8. Nov 1, 2006

### wywong

Any matter that comes out of the event horizon must have velocity greater than the escape velocity there which is c, and doing so violates GR.

Wai Wong

9. Nov 1, 2006

### taylaron

all that matter has to go somewhere.

10. Nov 1, 2006

### cesiumfrog

Actually, it is possible for matter to come out of a "black hole" (hence the term white hole). Just as we can observe a particle falling in (and calculate that it will take an infinite amount of time to reach the event horizon) we can also observe a particle falling out (and calculate that it has taken an infinite amount of time to travel from the event horizon.. but came from it none the less). The relevent GR solutions are time symmetric (particularly in Kerr geometry I think a single geodesic can fall in and then back out..).

On the other hand, it is an accepted assumption that any existing black holes actually formed (at a finite time in our history) from collapsing matter and thus are not actually symmetric in time. It's also reasonable to expect that any singularity cannot be correctly described without a more unified quantum gravity theory. As far as I'm aware it is baseless conjecture to suppose any connection to other universes.

11. Nov 2, 2006

### Phobos

Staff Emeritus
All that matter goes into the mass of the singularity. There's no known exit. (of course, we don't know everything about singularities)

12. Nov 2, 2006

### Labguy

Matter from a BH is not coming out of the event horizon (EH). There are two methods where matter can radiate from a BH, and Hawking Radiation is the most well-known. In this case, any escaping matter is created just outside the EH and sometimes, one of two virtual particles can escape while the other falls back below the EH radius. The escaping particle becomes a "real" particle and the BH loses a small amount of mass as a result of the loss of the particle.

The other method, where two virtual particles can escape at the same time and become "real" particles has been discussed many times before on PF (as has Hawking Radiation).

13. Nov 5, 2006

### ukmicky

OK i'm only an interested amateur and i understand that nothing can escape back through an EH but why cant something like another universe of some form exist within the EH. why cant the event horizon be the boundary encircling a new universe with different properties laws etc to ours.

14. Nov 5, 2006

### cesiumfrog

Sure, it's possible. It's also possible that there's a pink elephant standing right behind you. There's just no particularly good physical reason for us to predict either of those things to be true.

15. Nov 5, 2006

### ukmicky

But if you go back through history there are many occasions where scientists were ridiculed for suggesting things which the science community though were highly unlikely only for the ridiculed scientist to be proved right.

Wasn't the man ( cant think of his name )who first discovered and suggested that gamma ray bursts were coming mainly from outside our galaxy ridiculed and placed into the pink elephant club for his discovery as they thought there was no good physical reason for the science community to predict his discovery was true as they thought the energy requirements would be to great.

OK i understand the chances are we are not in a black hole however we cant tell for sure, we don't know whats beyond the EH, just because our universe works in the particular way which it does doesn't mean there cant be others which work under different rules and scales.

Last edited: Nov 5, 2006
16. Nov 5, 2006

### cesiumfrog

It's not about what the community believes likely or unlikely, but whether there or not there is a physical reason (a theory supported by previous experimental results) to predict it.
A discovery shouldn't be ridiculed, since it implies there is already experimental proof. As for the second claim (origin of an effect), if he had no physical reason then I don't think a guess should have been taken seriously (even if it later turned out to have been a lucky guess). Of course in the real world things are a little less clear and we mightn't trust any discovery before an independent laboratory has replicated it (depending, perhaps, on people's past reputations).

Anyway, the extra universes thing is more an example of Ockam's razor. They might be there, but since the currently best verified theories don't seem to predict any such thing, everyone's going to assume for the time being that the only thing black holes might contain are collapsed stars.

17. Nov 7, 2006

### Hilton Ratcliffe

Hi everyone,
On the question of black holes, I must ask by what physics you suggest that black holes with their concomitant singularities exist at all? Singularities are physically impossible, requiring divide-by-zero. Black holes are therefore also physically impossible, and all observational phenomena attributed to so-called “supermassive black holes” (manifestations of hyper-gravity) can be adequately explained by other means, notably compact objects.
While he was at Princeton, Einstein himself published a paper from which the following abridged quotations are drawn (A. Einstein, "Annals of Mathematics", vol. 40, #4, pp. 922-936 October 1939). The term “black hole” was at that stage not yet in use.
Quote: “If one considers Schwarzschild's solution of the static gravitational field of spherical symmetry..,[g_44] vanishes for r = m/2. This means that a clock kept at this place would go at rate zero. Further it is easy to show that both light rays and material particles take an infinitely long time (measured in 'coordinate time') in order to reach the point r = m/2 when originating from a point r > m/2. In this sense the sphere r = m/2 constitutes a place where the field is singular.
“There arises the question whether it is possible to build up a field containing such singularities with the help of actual gravitating masses, or whether such regions with vanishing g_44 do not exist in cases which have physical reality...
“One is thus led to ask whether matter cannot be introduced in such a way that questionable assumptions are excluded from the very beginning. In fact this can be done by choosing, as the field-producing mass, a great number of small gravitating particles which move freely under the influence of the field produced by all of them together. This is a system resembling a spherical star cluster. ... The result of the following consideration will be that it is impossible to make g_44 zero anywhere, and that the total gravitating mass which may be produced by distributing particles within a given radius, always remains below a certain bound…
“The essential result of this investigation is a clear understanding as to why the 'Schwarzschild singularities' do not exist in physical reality. ... The 'Schwarzschild singularity' does not appear for the reason that matter cannot be concentrated arbitrarily. And this is due to the fact that otherwise the constituting particles would reach the velocity of light.
“This investigation arose out of discussions [with Robertson and Bargmann] on the mathematical and physical significance of the Schwarzschild singularity. The problem quite naturally leads to the question, answered by this paper in the negative, as to whether physical models are capable of exhibiting such a singularity." Endquote.
Halton Arp put it very nicely: “In its usual perverse way all the talk has been about black holes and all the observations have been about white holes.” (“Observational Cosmology: From High Redshift Galaxies to the Blue Pacific”, Progress in Physics Vol 3, October 2005)
Energy and gravitation from neutron stars can in principle adequately explain what we see, and I feel it unnecessary to use this or any other phenomenon to explain unseen, hypothetical add-on entities like Big Bang, singularities, and infinitely curved spacetime.
Best regards,
Hilton Ratcliffe
Astronomical Society of Southern Africa.

18. Nov 7, 2006

### cesiumfrog

Yes, almost all of the "evidence for black holes" is actually just evidence for compact heavy objects (though I'm not certain whether this includes signals from inspiralling binary systems, and things may further change if we have any success in gravitational wave astronomy).

However, almost all of the available evidence also indicates that general relativity is correct (especially on planetary scales), and the theory predicts that if it is possible to produce something sufficiently heavy and compact (which nobody doubts in principle) then there should be an event horizon around that object (and furthermore, when any object crosses the horizon, it should be drawn inexorably further inward).

I think it's widely assumed that a more realistic theory of quantum gravity may (likely) avoid the central singularity issue, but it seems unlikely (in light of the success of general relativity on larger scales) that it could be impossible to create objects with event horizons. If you accept that event horizons can in principle be created, it's not a big step to infer from compactness of some heavy dark objects that those quite probably are "black holes".

Last edited: Nov 7, 2006
19. Nov 8, 2006

### Hilton Ratcliffe

Hi Cesiumfrog,

Thank you for your comment, and an interesting line of thought.
The theoretical basis for black holes was derived from the Schwarzschild metric, and includes as a critical principle a central singularity. I would like to suggest therefore, since we appear to agree that singularities are presently undesirable in astrophysical theory, that we ignore black holes for purposes of interpreting observational data. This is not as onerous as it might sound. It simply requires broader vision. MOND gives us the means to cope with galactic rotational anomalies as an effect, and is already in use by my colleagues at the European Southern Observatory. There is no need to invoke dark matter. The empirical method in astrophysics is hampered by our apparent inability to look across the boundaries separating various research disciplines, and in my own case, my work went off on a tangent because of my relative ignorance of nuclear chemistry and electrical field theory, both of which cannot be ignored by astronomers attempting to explain astrophysical phenomena. We cannot, for example, leave out the nuclide evidence in Moon rock, meteorites, and solar wind pointing to the chemical composition of the body of the Sun beneath the photosphere, nor can we not take into account electrical force when assessing rotation and cohesiveness in stellar systems. In both cases, we may with confidence extrapolate lab results and local experience to objects further afield. Let us not base our interpretation on theories that depend upon patently irrational things in the faint hope that quantum gravity (itself not a sure thing in our lifetimes) might possibly resolve the dilemma.
Your argument regarding event horizons is interesting. An event horizon marks the orbital radius of a massive object at which the escape velocity is c. Special Relativity is assumed, and the event horizon is a point of no return for anything, radiation included, which visits it. However, as Einstein explains in my previous post, combining SR and GR makes the dynamics such that a black hole would not be able to accrete. Even without our problematic singularity, black holes cannot work as suggested in galactic models that use them (of course, this assumes both theories of relativity and ignores supernatural or purely hypothetical arguments).
Regards
Hilton

20. Nov 8, 2006

### cesiumfrog

I disagree with that (as one who has hand calculated that metric as a 3rd year assignment, assuming little more than symmetry and the surrounding vacuum). Theoretically the external result seems just as valid as the equivalent Newtonian solution (ie. $G m_1 m_2 r^{-2}$ also has a singularity) and in practice we have our solar system in which to further confirm how well any solution matches reality.

The Schwarzschild solution shouldn't really apply to galaxies as a whole because instead of the vacuum you have a clumpy matter distribution. I think it's just the difficulty in accurately treating the latter that is turning astronomers to MOND for the moment. As for your quotes regarding accretion, I'd just point out that a lot of important work has been done regarding black holes in the time since the term was invented.

Is your eagerness to exclude black holes sufficient for you to reject SR or GR completely?