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DTMark

Gravity And Black Holes

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Watching BBC4 tonight - interesting programme about black holes, with some genuinely new stuff. At least I hadn't heard it before.

My brain then sets about solving the problems that nobody has ever managed to come anywhere close to solving. There's a problem of expectation management there.

What always surprises me about these things, and it's probably just the way the programme is sequenced, is that the "obvious" conclusion which many would get to in five minutes doesn't come until the end.

In this case - the discovery that black holes are central to galaxies, and their gravity impedes the growth of that galaxy. Logical.

Fast forward... the black holes consume the galaxies.

The black holes consume each other.

Now there's only one black hole out of which, if history repeats itself as we understand it, all the matter will spew back out again in another Big Bang thus forming a new universe. That's how it all started, isn't it?

Not convinced, personally. Nor am I convinced that the matter which goes into a black hole actually stays there and doesn't "pop out of the other side". I think this is Hawking's theory and it seems logical to me. Black holes are entry and exit points from the universe. Though not of the type which living matter could ever utilise, and we'll never know.

Central to all of this is gravity.

So I then thought "What causes gravity" and I then find that nobody knows the answer to that either.

Anyone here know?

;)

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I studied Physics/Maths and I don't know! :blink:

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I studied Physics/Maths and I don't know! :blink:

I did GCSE. I still recall the argument with the physics teacher when he asserted that "energy can change form but can never be destroyed" which everyone immediately took issue with but was explained by the cop-out of something called "potential energy".

In other words if you use energy to lift something up and put it on a shelf, potentially it has the energy to fall back to the ground again. Your energy has become potential energy in that object. Or something like that. It sounds so ridiculous I wonder if I remember that right.

Someone will know.

People here know everything.

;)

This is as near to an explanation as I have found.

http://www.science20.com/hammock_physicist/it_bit_entropic_gravity_pedestrians-66244

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there is no time in the black hole.

So the other side is the time the black hole dies.. either the beginning or then end of the universe...or both.

maybe

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Anyone here know?

;)

According to Einstein, Gravity is an inertial force caused by the deformation of spacetime by matter. Which just pushes the question back to: "What, exactly, is spacetime?"

Needless to say it doesn't work well as a theory at the smallest levels so the quantum theory modelling people have different (competing) theories. If anyone discovers a graviton they'll no doubt supplant the accepted explanation.

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According to Einstein, Gravity is an inertial force caused by the deformation of spacetime by matter. Which just pushes the question back to: "What, exactly, is spacetime?"

Needless to say it doesn't work well as a theory at the smallest levels so the quantum theory modelling people have different (competing) theories. If anyone discovers a graviton they'll no doubt supplant the accepted explanation.

driving a car doesnt work at atomic levels either.

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The answer is obvious...'God'. :rolleyes:

I think a more pertinent question (which is where you are going) is how did the rules themselves come about? Did the rules of the universe exist before the universe itself? How could that be?

How long did we have to wait until time was invented?

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Guest eight

So I then thought "What causes gravity" and I then find that nobody knows the answer to that either.

Anyone here know?

;)

I reckon gravity is getting stronger. Anybody else feel the same?

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The answer is obvious...'God'. :rolleyes:

I think a more pertinent question (which is where you are going) is how did the rules themselves come about? Did the rules of the universe exist before the universe itself? How could that be?

what rules?

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It is possible that everything that has ever happened and will ever happen is happening right now.

If you then throw in the mulitiverse alternate reality theory where every possible random event is happening in some alternate reality - i.e. a universe exists where we are all property owning billionaires or one where there are no deluded old scrapper birds on dating sites - then everything that can happen, has or will happen is happening right now.

So what is perceived, by your puny human brains (Oops!) - as Time is simply now and that rather than going back and forward in Time all we have to do is acess another part of reality right now.

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According to Einstein, Gravity is an inertial force caused by the deformation of spacetime by matter. Which just pushes the question back to: "What, exactly, is spacetime?"

Needless to say it doesn't work well as a theory at the smallest levels so the quantum theory modelling people have different (competing) theories. If anyone discovers a graviton they'll no doubt supplant the accepted explanation.

Perhaps therein lies some of the problem. If I'm trying to work something out or predict something then the logical way to do that is to look at things which are similar e.g. that which is observable, and perhaps that's one of the reasons why we have never solved this. "The laws of physics are the same everywhere in the universe". You cannot assert that, can you. Not before you can explain space time and gravity, for a start.

And I think you're on the right lines with space time. Although I'm not qualified in all of this, space time is the one bit I can never accept fully. I can comprehend the explanation and the experiment with the atomic clock but I am not convinced we have this right.

That time is a "thing". Rather than simply a word applied to describe a portion of events which occurred in a sequential fashion e.g. it is a "nothingness", not a "thing". If that makes any sense. In theory you look back in time every time you look at the night sky and if you had a powerful enough telescope you might be able to see backwards in time on another planet, though not interact with it. That would suggest that nothing can influence it. Which is where my theory falls down.

Exactly. You get my drift. ;)

Does it mean the concept of time existed before it existed itself.

We really need to breed a number of Einstein brains and link them together in a parallel formation.

That's you lot.

I reckon gravity is getting stronger. Anybody else feel the same?

Are you just eating more ;)

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3.5x joint salary

there are more banking rules ignored than there are grains of sand on every beach in the world.

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I've always thought it was rather arrogant, and stupid, for scientists to look at the vastness of the Universe - which our knowledge of it seems to define it as bigger and bigger by the day - and say "Oh, the laws of physics are the same everywhere" because there is simply no scientific evidence that this is so.

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It is possible that everything that has ever happened and will ever happened is happening right now.

If you done throw in the mulitiverse alternate reality theory where every possible random event is happening in some alternate reality - i.e. a universe exists where we are all property owning billionaires or one where there are no deluded old scrapper birds on dating sites - then everything that can happen, has or will happen is happening now.

So what is perceived, by your puny human brains (Oops!) - is that rather than going back and forward in Time all we have to do is acess another part of reality right now.

I do like this theory but I think it's the least likely explanation.

But then on what am I basing that assertion?

Nothing, really. Why my gut instinct would be better than the greatest physics experts would need some explaining.

If it were true however then in theory we could travel in time. That's why I don't think it's true. And yet we have proven, on a very small scale, that time travel to the future is in fact possible and we theorise that if we flew fast enough around the perimeter of a black hole and returned to earth, we would have travelled into the future. Though we do not know that to be true and it's impossible anyway as we understand it.

A side question:

"Nothing can escape a black hole"

OK. So, The Big Bang theory is wrong, then? You can't hold both to be true, surely?

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I've always thought it was rather arrogant, and stupid, for scientists to look at the vastness of the Universe - which our knowledge of it seems to define it as bigger and bigger by the day - and say "Oh, the laws of physics are the same everywhere" because there is simply no scientific evidence that this is so.

Its not getting bigger..time is slowing down, so it looks like its getting bigger.

With zero speed of time, the universe would fit inside a photon.

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I did GCSE. I still recall the argument with the physics teacher when he asserted that "energy can change form but can never be destroyed" which everyone immediately took issue with but was explained by the cop-out of something called "potential energy".

In other words if you use energy to lift something up and put it on a shelf, potentially it has the energy to fall back to the ground again. Your energy has become potential energy in that object. Or something like that. It sounds so ridiculous I wonder if I remember that right.

You remember it right, however something my physics teacher came out with will upset you even more.

Because every object has gravitational attraction to every other object, there is a measure of potential energy, between any two objects. This measure increases with distance, i.e. the further apart two objects are the greater the energy that would be released should they fall towards each other. Now, if at infinite distance the potential energy is zero then at any finite distance the energy between any objects is actually negative. My teacher's idea was the sum of all this negative potential energy is stupendous (it exists between every two objects, I suppose where an object is defined as the smallest type of particle still subject to newtonian physics) and in fact equals all the other energy in the universe. The total amount of energy in universe is therefore zero and existence is a thermodynamic free lunch.

(Yeah, there are at least two massive assumptions there.)

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According to hawking, black holes eventually evaporate over an incredibly long period of time. (Hawking radiation.)

Over a longer period of time, all subatomic particles will possibly decompose into photons.

The Universe will be nothing but light, with nothing for it to shine upon.

It will be the faint glow at the back of God's wardrobe, behind that jacket that doesn't fit him any more.

It will be sold on EBay for 99p.

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Guest eight

Gravity is only there to enable our bodies to be attached to the earth....no body no gravity required.

I expected your contribution to this thread to be more along these lines....

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> So I then thought "What causes gravity" and I then find that nobody knows the answer to that either.

> Anyone here know?

Well the latest hot theory is that gravity is a manifestation of information. Google 'holographic principle'.

For example:

"The holographic principle was inspired by black hole thermodynamics, which conjectures that the maximal entropy in any region scales with the radius squared, and not cubed as might be expected. In the case of a black hole, the insight was that the informational content of all the objects that have fallen into the hole might be entirely contained in surface fluctuations of the event horizon. "

Aside from that I would commend Bloo Loo's observation that a universe with no matter and just radiation would fit inside a single photon. Extrapolate from there to a big bang...

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