1. Jul 23, 2004

### Ian

If the suppsed Hawking Radiation truly exists then since all matter was supposedly concentrated into a singularity in the time before the big bang (if there was one); then this single black hole must have evaporated away according to the rules that govern Hawking Radiation.

To me this seems to say that theoretically there cannot have been both a big bang and Hawking Radiation - one does not exist, but which one?
There is a horrifying (if not hilarious) problem here: If Professor Hawking's math is correct (the guy is a brilliant with numbers) then much of 20th century theory must curl up and die!

Besides, what happens when a black hole evaporates through HR down to the mass of a proton? We have never observed proton decay, so why should a singularity of same mass as a proton decay by HR?

2. Jul 23, 2004

### Phobos

Staff Emeritus
A black hole singularity is different than the Big Bang singularity (an object embedded in spacetime vs. spacetime itself).

3. Jul 28, 2004

### Ian

Phobos,
Why is there a difference? Matter is matter, and space-time is space-time, the interface between the two must always remain constant.
To present a difference between a black hole and the big bang singularity is a theoretical dodge.

4. Jul 28, 2004

### devilmech

There is no theoretical dodge. The singularity of a black hole is fundamentally different from the big bang singularity in that the singularity of a black hole exists in space-time, which gives it a reference frame, and thus can be observed in theory. The big bang singularity had no reference frame, as the concept of space-time is a result of the big bang itself, and therefore there is no observable reference frame for the big bang singularity. You can effectively view a black hole as as a vector $$\vec{y}$$ with it's endpoint at some non-zero point on a vector $$\vec{x}$$, with $$\vec{x}$$ being the big bang singularity and having it's endpoint at the origin, or zero.

5. Jul 29, 2004

### Ian

If the big bang singularity had no reference frame, it simply cannot be observed in theory - i.e. it can never have happened.
You can't have it both ways!

If theory extrapolates backward to a big bang singularity of matter, it must also extrapolate backward to a 'space-time singularity' in conjunction with the matter singularity.

6. Jul 29, 2004

### turin

I cannot observe the birth of my parents. So they were never born?

7. Jul 29, 2004

### Olias

If one rewinds our Galaxy,(without reference to other far away current Galaxies), then there comes a defined Horizon, wherby there is extreme particle creation. This is centered around the Blackhole that we deemed to be at our Galactic core, in a time-reversed manner.

The compaction of our Galaxy to such a phase of Virtual pair creation, has in this sense a 'perfect' background for particle creation, which is on the scale of a tear in the fabric of space, (not to be confused with a tear in spacetime) the Big-Bang is the moment of our Galaxy Creation, the singularity centered at our 'current' Milky Way, has its own seperate Spacetime, far far away from other Galaxies.

If one rewinds Einstein Field Equations, then each Galaxy has seperate spacetimes, only Galaxies that can be rewound and actually collide at the same instant (within the same time reversed horizon of EM Vacuum space) would share a percieved same "Big-Bang" Universal Instant.

If one Rewinds all of the actual Universe, which is supposed to be current accepted version of events, then one cannot explain how some Glaxies will not merge into the same 'singularity' at the same given instant, the moment of Universe Creation.

Just look at Andromeda, it is currently Heading towards us, if one could stop it in its tracks along with our Milkyway, then rewind both Galaxies in a Time-Reversed fashion, their proximity to each other will actually seperate Exponentially, the farther back in time you rewind the Universe, the further Andromeda and the Milkyway will Seperate. How can their creation be at the same instant if they are moving away from each other in a time-reversal scenario?

If every single galaxy in the observable universe were actually moving away from each other, then I would conceed that any Time-reversal of the Big-Bang would infact produce a single instant of all Galaxies, and all Galaxies would share the same birthdates!

8. Jul 30, 2004

### marcus

Ian this doesnt make sense and appears to be based on a misconception about what a "singularity" is, misinformation about what cosmologists assume.

You say you live in the UK. Probably you pay taxes or members of your family do. Some of that tax money goes to support research in cosmology.
If you care at all about cosmology issues, why dont you find out what's going on?

A singularity is not something in nature. It is something that occurs in a human-built theory. It's just a point or region where the theory breaks down.
The two famous kinds of singularity are failures in General Relativity (the classical 1915 GR fails at the big bang and at black holes) and there is an on-going effort to fix these failures and get rid of the singularities in GR.
Other theories can have singularities too but the famous ones nowadays are flaws in GR.

Cosmologists do not assume that the BB began with a singularity. How could they, when such a thing does not happen in nature? It is just a flaw in theory that they are in process of eliminating. The current picture is more of a changeover from contraction to expansion----a reversal----the word "bounce" has been used----it is risky to use metaphors like "bounce" or "bang" but media and the journalistic imagination seem to demand some catchy metaphor. I prefer the plainer word "reversal" for the crossover from contraction to expansion believed to have happened at the time where there used to be a singularity in the theory.

---------
when you buy a shirt at the store it can have various kinds of defects
a seam might not have been sewn
a button may be missing etc.
singularities are flaws and there are different types
In Gen Rel the bb singularity is different kind from the bh one. Just because there is a BB singularity at the time of BB does not mean that this is the same thing as a BH! So one would not expect Hawking radiation! That is totally illogical.

You seemed to be arguing that way in your post. Like you buy the shirt and you find that a seam was not sewn and a sleeve is coming loose---so you conclude that therefore button must be missing.

It does not follow. (there might be a connection between the two types of singularity but we dont know that yet)

In any case remember that the flaws are in the theory, not nature, so we cant draw much in the way of conclusions from them until the experts fix the flaws and check the corrected theory out by observations or experiment.