Dumb question

[Ags]

How did the big bang go bang? If nothing can escape a black hole, and all matter was originally concentrated into a singularity, how come the universe is expanding? In fact, how come is it expanding so much it won't even collapse back on itself?

[Ags]

Bump!!! Somebody must know, c'mon :-)

Is this what it's like being stuck inside a black hole? Who would have thought it could be so nice?

[Stu]

Hi Ags

Not sure anyone knows exactly what caused the big bang in the first place. All I know, just to get the conversation going, is that it wasn't a 'bang' as in an explosion, but a very rapid expansion of space from a singularity.

The one thing that has always confused me is about the supposed acceleration of the expansion ie the further you look, the faster the expansion is happening. I understand how we see that observationally (made up word?) but we are seeing that light from 13 odd billion years ago so how so we know what's happening out there now? Could the universe already be contracting? As long as it was contracting slower than the speed of light, we wouldn't know would we?

Stu

[Ags]

I understand it wasn't actually an explosion, but if it takes infinite energy to get out of the gravity well of a singularity / black hole, then how did all the stuff in the universe expand outward from the initial singularity? I call it a dumb question, because I am sure it is the first problem a cosmologist must consider when thinking of the big bang - I have just never heard an answer.

The tendency of distant stuff to recede faster, isn't that the Hubble Constant? That is just the expansion of space time we are seeing, and it is cumulative over distance so distant things seem to receed faster.

[assasincz]

Many of such fundamental questions are comprehensibly explained in Astronomy Cast podcast, which I actually find fantastic!

Astronomy Cast

[Stu]

You are right of course Ags, but I am still not sure that anyone has an answer to that question. I suppose the difference is that the big bang singularity had potentially infinite energy to drive the expansion of space-time, rather than trying to escape the gravitational pull of a black hole.

I also get the reason for the faster expansion being related to distance but still don't get how we know what's going on out there now.

Stu

[JulianO]

The laws of physics fail very close to the big bang, so they don't really work there. Hence they can't explain things at that point. They go back to about 10^-43 seconds after the big bang, which is far better than any device can measure in time, but after that you're into new physics.

All we can say is playing the 'tape' backwards - everything seemed to come from a single point, but quite what caused that, and quite whether it was anything like a modern day black whole is anyones guess.

It may well not have been a singularity. Consider an stick of dynamite gong bang, and you looking at it after a second. You can see everythign is flying outwards, so playing the tape back makes you think it was a singularity, b ut actually other things happened at time 0.

[Jessun]

Can't remember the reference here, just remember reading that the man who coined the phrase 'big bang' to illustrate the theory nowadays isn't very keen on the choice of those words, and not even keen on the whole idea...

A bang of sort, and 'inflation' is the flavour of the day.

[Capricorn]

May be simplistic but where is it proven that it came from a singularity?

The graph of the expansion and so the reverse back in time showed that the universe had a start, it is however a graph of time not size. In the ideal state it has an origin of 0,0 but that is just an ideal state.

Perhaps a 1/1000 lightyear is small enough to be a "singularity" in the scale of the pop.

Never feel happy with the term singularity, it seems to be used too much, yet 0 in maths or physics is an area fraught with disaster.

[JulianO]

Fred Hoyle coined the term big bang, when it was a tussle between his steady state model and the now big bang theory.

[steelfixer]

My thoughts on black holes always tend to end up with the view that no matter how large or small they are there must be a point that they cannot consume any more matter.

When that point is reached surley the process must be reversed and with so much compressed matter the reversal would be of cataclismic propotions.

A bit like a balloon bursting only in reverse.

[Ags]

I think black holes just get better at being black holes as they get larger.

For example the hole at the center of the milky way has the mass of 6 million suns and will only get bigger. In 2013 it will devour a cloud of gas three times the mass of earth - it is amazing that such a small object can be detected so far away.

[acey]

May be simplistic but where is it proven that it came from a singularity?

It was proved by Penrose and Hawking subject to various assumptions, in particular that general relativity holds (though most people now assume that it wouldn't hold during the earliest moment).

Penrose?Hawking singularity theorems - Wikipedia, the free encyclopedia

As to the original question: nobody knows why it went "bang" (there are various views on this). As to why it didn't immediately become a black hole, the mistake is to think that the bang was a particular point in space, whereas (in the tiniest moment after the bang) it is all of space: you effectively have a very dense uniform fluid everywhere, with no point at which a black hole would form.

BTW, two record-breaking supermassive black holes have been newly discovered in the galaxies NGC 3842 and 4889, both observable with amateur scopes (the galaxies, that is, not the black holes!). They're in Leo and Coma.

http://www.sciencedaily.com/releases/2011/12/111205140609.htm

http://www.guardian.co.uk/science/2011/dec/05/supermassive-black-holes-discovered-space

[ollypenrice]

I was going to come in with an amateurish variation (I think!) of Acey's point.

In the OPs original question there is the idea of a singularity AND a black hole around it. Remember that a singularity is not a black hole, it is the source of the gravitation which creates the black hole around it (out to the Schwarzchild radius).

Now I would suppose that this is not the case for the BB singularity, if it existed. There IS no space around that initial singularity. All that there is lies within it. There is nowhere for a black hole to be outside it.

I'll always stand corrected...

Olly

[steelfixer]

This might sound stupid but what if the so called big bang was not the origin of all things but mearly a rebirth of an exsisting entity.

What if it is just a natural cycle.

What if a super black hole type thing had consumed the entire universe untill it reached a point I suggested in my earlier post.

Would this not produce a single point for the birth of our universe.

A rearly simplistic thought I know but what if ????

[acey]

The cyclic universe was widely postulated in the early days of big bang theory (i.e. 1920s-30s) but has problems with entropy: the cycles would run out of steam. In a different form it has breen revived in "brane-world" scenarios.

Cyclic model - Wikipedia, the free encyclopedia

John Barrow's recent book "A Book Of Universes" discusses a lot of these early models that physicists considered - and which often naturally occur to people nowadays as possible alternatives to the standard model. I thought it an excellent book.

http://www.amazon.co.uk/Book-Universes-John-D-Barrow/dp/1847920985/ref=sr_1_1?ie=UTF8&qid=1324122400&sr=8-1

http://www.scotsman.com/news/book_reviews_the_book_of_universes_the_hidden_reality_1_1494601

[ollypenrice]

Another John Barrow admirer here. He's a friend of some friends and I always hoped to meet him before leaving the UK but sadly never did so.

Olly

[steelfixer]

Thanks for the link Acey I will have to get that it sounds like an interesting read.

[JulianO]

Another model of the universe which is cyclic and compatible with most current observations is the Ekpyrotic one.

There are some subtle properties of the CMB that should eventually help distinguish it.

[dynamo]

the mutiverse is all the rage with physicists.

specifically, we're experiencing an instant in 'time' in one of an infinite number of parallel universes.

every time we make a decision, e.g. to turn left on a road instead of right, in another, parallel universe, we chose to turn right and our lives are completely different.

the universe(s) have always been here and always will be, we're just observing a 'moment in time' according to our life choices.

some even believe, with proper training and "awareness", that we can chose to live in another one of our parallel universes at any time, thereby having new memories and no recollection of our previous, so to speak, existence.

as stated in another post , modern physical was do not apply, as being observed when searching for he "god particle", the boson, at the CERN facility.

wild stuff indeed.

[Ags]

You can calculate the intensity of the gravitational field by calculating the gravitational force exerted by every bit of matter near you. The forces can cancel out - one of the satellites observing the Sun floats in the tipping point where Earth and the Sun's gravity balances. Likewise if you travelled to the center of the Earth, you would be in free fall as the gravitational pull from each part of Earth would cancel out.

At the beginning of time, the universe was incredibly dense and everything had lots of matter nearby to exert a force. But as every point in the new universe was equally far from everywhere else, the gravitational forces would cancel out and everything would be in free-fall, just like the miner at the center of the earth.

I think this is true for three dimensions, but I think if the universe is curved in a higher dimension, then the gravity should also cause a force in that higher dimension, causing the universe to collapse or crumple up. For example, if you imagine a two dimensional universe curved into a three dimensional sphere. The universe is covered with a network of ropes and pulleys, forming a pattern like the hexagons on a football. If the pulleys start pulling in the ropes, each intersection in the network does not move because the pulleys pull them equally in all directions (the intersection experiences "zero g") but the balloon will get smaller as the rope tension increases. The two dimensional space-time of my example contracts and the universe ultimately returns to a singularity.

I guess... :-)

[Scosmico]

The Big Bang equation: BγG.ΕGΘ²=Ø

ByG.EGO stands for young physicist's ego.

Ø = absolute Zero in 4D.

[acey]

You can calculate the intensity of the gravitational field by calculating the gravitational force exerted by every bit of matter near you. The forces can cancel out...

That's pretty much how I understand it. The nuance is that in general relativity gravity is caused not only by mass, but also by energy, pressure and stress (i.e. the stress-energy tensor), plus there can be background gravitation without a physical source (e.g. cosmological constant).

But the point is that in the immediate moment after the big bang, everywhere was effectively at the same density, there wasn't a very strong source at a particular point which could cause a black hole to form.

There were indeed variations - gravitation wouldn't have cancelled out completely. But those variations were quantum fluctuations, very small and not significant initially. They got magnified by inflation (in a fraction of a second) and eventually became the places where matter slowly concentrated into proto-galaxies. That took millions of years. The centres of those (proto-)galaxies eventually accumulated enough matter to become the supermassive black holes now observed in galaxies.

[Ags]

Magnified by inflation? I thought inflation was introduced as a concept to explain the smoothness of the universe, not the reverse?

[JulianO]

Magnified by inflation? I thought inflation was introduced as a concept to explain the smoothness of the universe, not the reverse?

Smoothness in terms of temperature, rather than lumpyness. It explains why its nearly all the same temperature, as once everything was very close together - so could be the same. What it does do is take the tiny quantum perturbations and magnify them into something visible at the macroscopic level.