Thread: Bigcrunch theory again, help me understand why scientists believe the universe is finite.

Im a firm believer in the big crunch theory, not because I wish it to be true but because it just seems logical.

The bigger the black holes - the bigger the strength of the pull is right?

Our galaxy is circular shaped, the mass of a galaxy rotates around the centre which is filled with black holes (They seem to bring order, not chaos) The universe doesent just "fade away" because of this. So I would think that at one point the gravitational forces should pull the entire universe back in and restart with a new big bang.

Why do scientists believe in that enthrophy theory that everything will just flat out and die in cold space?

That the expansion of the universe accelerates is a poor argument. Ofcourse it accelerates! If the big bang was an explosion than the force will increase at high speed, but this doesent mean that when it burns out it wont collapse on itself. Just because it accelerates now doesent mean that wont change! It seems scientists fail to understand cosmic time? For all we know the universe could accelerate faster and faster for a trillion years, then slow down, and use the same time to retract.

Everything has an opposite. Cold - warm, tall - short - the list goes on. Why shouldnt explosion have an inevitable implosion as an opposite?

It seems scientists go "It accelerates now so it must accelerate forever until it dies out"

Originally Posted by Raziell

Im a firm believer in the big crunch theory, not because I wish it to be true but because it just seems logical.

It may seem "logical" (whatever that means) but currently the evidence doesn't appear to support it.

The bigger the black holes - the bigger the strength of the pull is right?

Yes. But it is no greater than that of the mass that formed the black hole. They doesn't have any more gravitational pull than any other equivalent mass.

Our galaxy is circular shaped, the mass of a galaxy rotates around the centre which is filled with black holes

As far as I know there is only one (large) black hole at the center of the galaxy. And the galaxy would continue pretty much unchanged if it wasn't there. It is a minute fraction of the mass of the galaxy. It is not as if the black hole is holding everything together.

So I would think that at one point the gravitational forces should pull the entire universe back in and restart with a new big bang.

My understanding is that there doesn't currently seem to be enough mass to make that happen. (And it makes no difference if that mass is in a black hole or not).

That the expansion of the universe accelerates is a poor argument. Ofcourse it accelerates! If the big bang was an explosion than the force will increase at high speed, but this doesent mean that when it burns out it wont collapse on itself.

Well, the big bang wasn't really like an explosion.

Also, it seems the early universe was decelerating (due to gravity, presumably) but at some point relatively recently (a few billion years ago) it started accelerating. This is currently described as "dark energy".

Just because it accelerates now doesent mean that wont change!

True enough. But as we don't really know what is driving the acceleration, we can't really say.

It seems scientists fail to understand cosmic time? For all we know the universe could accelerate faster and faster for a trillion years, then slow down, and use the same time to retract.

It could. But with no evidence that is just speculation. It would be equally valid to suggest that it will accelerate faster and faster.

Everything has an opposite.

Extrapolating from everyday experience to the universe as a whole is not always valid.

Cold - warm, tall - short - the list goes on. Why shouldnt explosion have an inevitable implosion as an opposite?

On the other hand, why should it?

It seems scientists go "It accelerates now so it must accelerate forever until it dies out"

Not really. Scientists go, "that's odd; it appears to be accelerating now. I wonder what causes that ... and if it will ever stop ... or will it continue ... and ..."

Good answer, thanks.

It is so painfull to live not knowing.

This could be the 445893940003981th reincarnation of the universe and we wouldnt even know it. Or it could be the first and last. I'd happily chop off my left arm for the answer to it all

Originally Posted by Raziell

Im a firm believer in the big crunch theory, not because I wish it to be true but because it just seems logical.

The bigger the black holes - the bigger the strength of the pull is right?

Our galaxy is circular shaped, the mass of a galaxy rotates around the centre which is filled with black holes (They seem to bring order, not chaos) The universe doesent just "fade away" because of this. So I would think that at one point the gravitational forces should pull the entire universe back in and restart with a new big bang.

Why do scientists believe in that enthrophy theory that everything will just flat out and die in cold space?

That the expansion of the universe accelerates is a poor argument. Ofcourse it accelerates! If the big bang was an explosion than the force will increase at high speed, but this doesent mean that when it burns out it wont collapse on itself. Just because it accelerates now doesent mean that wont change! It seems scientists fail to understand cosmic time? For all we know the universe could accelerate faster and faster for a trillion years, then slow down, and use the same time to retract.

Everything has an opposite. Cold - warm, tall - short - the list goes on. Why shouldnt explosion have an inevitable implosion as an opposite?

It seems scientists go "It accelerates now so it must accelerate forever until it dies out"

I do not see the connection between the galaxies having a Black Hole in their nucleus and the expansion of space. By the way, the bigger the Black Hole the smaller the tidal forces you experience. The gravitational pull of a certain mass does not depend on how much you compress it.

Also, the collection of your "opposites" is more a philosophical analogy than actual hard science. Terms are man made. How warm is warm? How cold is cold. It is all a matter of perspective.

Putting this all aside, the very argument against a Big Crunch is that we actually see the universe expanding right now and there is no indication that it will change in future. Science is based on what we know and not on what we do not know. And the interesting thing is that the expansion seems to accelerate in our present epoch, while it did not in earlier times. So, there is no simple extrapolation possible from the beginning of the expansion and now. And no, the Big Bang wasn't necessarily an explosion. It is often popularised like this, but we actually do not know. For all that we know, there two forces competing with each other: one is pulling, one is pushing. And right now, the pushing part seems to take over. Whatever that really is, nobody knows. This is why we call it "Dark Energy".

Sure, it might be that the situation reverses in some distant future. But for now, there is no indication that it will. But this is how science works. The "knowledge" is constantly changing and updating.

Originally Posted by Raziell

Im a firm believer in the big crunch theory, not because I wish it to be true but because it just seems logical.

Logic is a good thing concerning science in general -- but observations trump both theory and logic. Present interpretations of observations are that the universe is expanding at an accelerated rate leading to a Big Freeze, and Big Rip disintegration, instead of being in, or returning to a steady-state condition, or a U-turn Big Crunch idea, or the infinite cyclic model of crunches and expansions, or other possibilities.

The bigger the black holes - the bigger the strength of the pull is right?

If you consider gravity a pull,? right !

Our galaxy is circular shaped, the mass of a galaxy rotates around the centre which is filled with black holes (They seem to bring order, not chaos) The universe doesent just "fade away" because of this. So I would think that at one point the gravitational forces should pull the entire universe back in and restart with a new big bang.

But as a whole they presently believe the universe works contrary to the actions and effects of gravity in the long run.

Why do scientists believe in that enthrophy theory that everything will just flat out and die in cold space?

This idea is based upon the concept that the universe as a whole works in accord with the second law of thermodynamics concerning a volume-expanding closed system. Again this is just theory, but presently it is thought by many to be the most likely model based upon present interpretations of collective observations.

That the expansion of the universe accelerates is a poor argument. Of course it accelerates! If the big bang was an explosion....

Maybe the idea of dark energy is a "poor argument" as you suggest based upon the available evidence, but it is the prevailing model presently called the lambda cold-dark matter Big Bang model, where lambda refers to the idea of an additional expansion factor (acceleration). The reason for this belief in this acceleration of the universes' expansion is not directly related to the BB idea as you suggest, however.

....Just because it accelerates now doesent mean that wont change! It seems scientists fail to understand cosmic time? For all we know the universe could accelerate faster and faster for a trillion years, then slow down, and use the same time to retract..................It seems scientists go "It accelerates now so it must accelerate forever until it dies out"

Based upon the interpretation of redshifts as being the expansion of space, they believe the universe is expanding. Based upon supernova interpretations and others, they believe this expansion is accelerating. Of course none of this could be true. And if valid does not mean that things won't change in the future as you suggest. But this is the current model for reasons explained. Even if there was constant expansion without acceleration, the results would be the same as it would be for accelerated expansion. It just takes longer without acceleration.

Everything has an opposite. Cold - warm, tall - short - the list goes on. Why shouldnt explosion have an inevitable implosion as an opposite?

I don't think your logic is bad but these ideas are just a philosophical perspective. Hot and cold, tall and short, positive and negative, etc. are not opposites. They are simply relative conditions to each other. Since contraction of volume could be called the opposite of expansion of volume, in this way your analogy has merit, but a number of concepts in physics are thought by most to be non-reversible, like entropy and time for instance.

Think of causality.

E = mc^2

According to relativity all things in the universe are connected to one another. Causal connectedness allows mathematics to be consistent.

c is a constant that reflects the proportionality of Energy/Mass

If the systems are causal, then in an infinite universe things start repeating. This implies that a perceived universe with defined physics is finite. There may be an infinite number of universes, but in our observable universe it is finite. New causal connections can evolve, but it is still repeatable and therefore finite.

Alternate dimensional physics do not necessarily have the same observable physics of what we consider to be our universe.

QES defines:
Cloned Universe - exact copy of physics and conditional outcomes
Parallel Universe - exact copy of physics with different conditional outcomes
Alternate Dimension - different physics in some way
Scaled Simple Causality - flat space-time without physics

Originally Posted by junkstopshere2

Think of causality.
E = mc^2

It should in this rather general context be mentioned that the above relation is only true for particles at rest. The full relation should read

Originally Posted by Strange

The bigger the black holes - the bigger the strength of the pull is right?

Yes. But it is no greater than that of the mass that formed the black hole. They doesn't have any more gravitational pull than any other equivalent mass.

Just a quick point/question. If black holes have no greater gravitational pull then that of the star that created it how come light is unable to escape the gravity of a black hole yet radiates from a star without problem?

Because the diameter of the star is around 2 million kilometers and the diameter of the BH (actually the event horizon) is about 12 kilometers. That means an incredibly higher density for the BH, and therefore a much more intense gravitational field.

Originally Posted by dmwyant

Originally Posted by Strange

Yes. But it is no greater than that of the mass that formed the black hole. They doesn't have any more gravitational pull than any other equivalent mass.

Just a quick point/question. If black holes have no greater gravitational pull then that of the star that created it how come light is unable to escape the gravity of a black hole yet radiates from a star without problem?

The bit that was missing from that was, "at the same distance". So, if the sun suddenly turned into a black hole, although it would get very dark, the planets would continue to orbit without change.

However gravitational force is proportional to mass (which we are assuming is constant here) and inversely proportional to distance-squared. So if a planet were half the diameter of Earth but with the same mass, the gravity at the surface would be 4 times greater.

If the sun were a black hole, its radius would be about 3km instead of 1.4 million kilometres. Which would make the gravity at the "surface" (event horizon) about 21 billion times greater.

So the mass stays constant but the gravity increases due to the increase in particle density?

Originally Posted by dmwyant

So the mass stays constant but the gravity increases due to the increase in particle density?

No, just due to the decrease in radius: you are closer to the center (classically, you can treat the source of gravity as the center of the sphere).

Also, black holes shrink and evaporate by giving off Hawking radiation.

Originally Posted by SowZ37

Also, black holes shrink and evaporate by giving off Hawking radiation.

For any stellar sized or greater black hole, the rate of addition of matter is far greater than the amount lost thru Hawking radiation. Any BH larger than micro sized grows. Any micro sized BH has already evaporated.

Originally Posted by AlexG

Originally Posted by SowZ37

Also, black holes shrink and evaporate by giving off Hawking radiation.

For any stellar sized or greater black hole, the rate of addition of matter if far greater than the amount lost thru Hawking radiation. Any BH larger than micro sized grows. Any micro sized BH has already evaporated.

After long enough, after the average temperature of the rest of the universe has dropped to almost nothing, even a supermassive black hole will start to lose more than it gains. I understood we were talking about the ultimate heat death of the universe, which is when black holes would evaporate.

You are correct.

Maybe. It depends how long the universe lasts. A stellar sized black hole would take about 60 Trillion years to evaporate by means of Hawking radiation. And that's without any additional accretion. Now, if M-theory is correct, and the universe exists on a brane, then 60 trillion years would be long enough for our brane to collide with another brane, restarting the universe. But the supermassive BHs will exist far longer than they have time to exist. Now, it the universe does reach the ultimate heat death, that would be it, and there'd be no energy available to radiate, so the BHs will simply sit there, quiescent, for all of eternity.

Originally Posted by AlexG

You are correct.

Maybe. It depends how long the universe lasts. A stellar sized black hole would take about 60 Trillion years to evaporate by means of Hawking radiation. And that's without any additional accretion. Now, if M-theory is correct, and the universe exists on a brane, then 60 trillion years would be long enough for our brane to collide with another brane, restarting the universe. But the supermassive BHs will exist far longer than they have time to exist. Now, it the universe does reach the ultimate heat death, that would be it, and there'd be no energy available to radiate, so the BHs will simply sit there, quiescent, for all of eternity.

Oh, that's right, Hawking radiation utilizes virtual particles/anti-particles outside of the black hole, not inside, in order to radiate. So if there were no more particles outside the black hole, it would jut sit there static?

Originally Posted by SowZ37

Originally Posted by AlexG

You are correct.

Maybe. It depends how long the universe lasts. A stellar sized black hole would take about 60 Trillion years to evaporate by means of Hawking radiation. And that's without any additional accretion. Now, if M-theory is correct, and the universe exists on a brane, then 60 trillion years would be long enough for our brane to collide with another brane, restarting the universe. But the supermassive BHs will exist far longer than they have time to exist. Now, it the universe does reach the ultimate heat death, that would be it, and there'd be no energy available to radiate, so the BHs will simply sit there, quiescent, for all of eternity.

Oh, that's right, Hawking radiation utilizes virtual particles/anti-particles outside of the black hole, not inside, in order to radiate. So if there were no more particles outside the black hole, it would jut sit there static?

Quiet as a sleeping baby. Forever. (maybe).

Originally Posted by AlexG

Originally Posted by SowZ37

Originally Posted by AlexG

You are correct.

Maybe. It depends how long the universe lasts. A stellar sized black hole would take about 60 Trillion years to evaporate by means of Hawking radiation. And that's without any additional accretion. Now, if M-theory is correct, and the universe exists on a brane, then 60 trillion years would be long enough for our brane to collide with another brane, restarting the universe. But the supermassive BHs will exist far longer than they have time to exist. Now, it the universe does reach the ultimate heat death, that would be it, and there'd be no energy available to radiate, so the BHs will simply sit there, quiescent, for all of eternity.

Oh, that's right, Hawking radiation utilizes virtual particles/anti-particles outside of the black hole, not inside, in order to radiate. So if there were no more particles outside the black hole, it would jut sit there static?

Quiet as a sleeping baby. Forever. (maybe).

Let me just check if my visualization of Hawking Radiation is correct. Virtual particle anti-particle pairs constantly generate in empty space. The universe can do this pretty much spontaneously, because it is still balanced, one particle to one anti-particle. Usually, they destroy each other making room for a new pair. When such a pair is close to an event horizon, they usually destroy each other or both fall in and cancel each other out. Sometimes, though, just one particle goes in which frees the other. The anti-particle stops being virtual for some reason (?) and so eradicates a particle inside the black hole. This allows the virtual particle to be a real particle. If it escapes the black hole's gravity, it is Hawking radiation. The particle didn't come from inside the black hole, not exactly. But it is only allowed to exist in a more permanent state is because a particle inside the black hole is gone. Is this more or less correct?

Also, without a frame of reference, (no more events occur, no more energy transfers, just an eternal static state,) do we just use words like eternity and forever for lack of a better term? Is it sort of a misnomer? I can't conceptualize time as meaning anything in a completely unchanging universe.

You pretty much got it, and I think I agree with you on time not having any meaning in an unchanging universe.

I think.

how you add pics???

Originally Posted by curious mind

how you add pics???

If you upload them to Photobucket, you just click the image link and paste it to the board. If you have a URL then:



and uncheck the box below the URL.

oh i see, before i could add them right from my pc ... ty.

Originally Posted by Raziell

That the expansion of the universe accelerates is a poor argument. Ofcourse it accelerates! If the big bang was an explosion than the force will increase at high speed, but this doesent mean that when it burns out it wont collapse on itself. Just because it accelerates now doesent mean that wont change! It seems scientists fail to understand cosmic time? For all we know the universe could accelerate faster and faster for a trillion years, then slow down, and use the same time to retract.

You don't have to have an accelerating expansion or something actively driving the expansion in order to have a continuing expansion of the universe. Once the expansion starts, it can continue on just from pure momentum. The mutual gravitational attraction of the universe will slow this expansion over time, but there is a threshold of density and expansion rate that will determine whether or not this would be enough to ever stop the expansion completely. It is a situation analogous to escape velocity. If I throw a rock up in the air, it will continue to climb until gravity slows it to a stop. However, if I could manage to throw it at a little over 7 miles/sec, it would never fall back. Gravity would still slow decrease its rate of climb, but this pull gets weaker with distance, and the deceleration falls off. The weakening pull of gravity never quite is enough to rob the rock of that last bit of speed it needs to in order to stop the rock.

The same thing can happen with an expanding universe. As the universe expands, its density decreases and so does the mutual gravitational attraction of its internal parts. If the initial density/ expansion rate is small enough, the gravitational attraction will lose out to the expansion. The expansion rate will slow over time, but never enough to halt the expansion completely.