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Old 03-10-2012, 12:49 PM
 
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Recently I watched a very interesting movie titled "Wonders of the Universe". In the movie the guy said that scientists claim the Universe will one day stop expanding and will accually dissapear. I forgot how he explained this but that's basically what he was saying. Well, I'm looking at a National Geographic magazine right now (November 2007) and in the article (Raising Heaven) it says, "They were expecting to find that the rate of expansion has slowed over the eons... instead, the astronomers were astonished to find that cosmic expansion is not slowing down at all: it is speeding up... it's as if a ball, thrown into the air, at first slowed, but then sped up and simply flew away. No natural force on earth can do such a thing - and none in the known universe could do such a thing.

The movie is more recent than the magazine. What's the deal.
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Old 03-10-2012, 04:25 PM
 
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Originally Posted by O-Ducky View Post
Recently I watched a very interesting movie titled "Wonders of the Universe". In the movie the guy said that scientists claim the Universe will one day stop expanding and will accually dissapear. I forgot how he explained this but that's basically what he was saying. Well, I'm looking at a National Geographic magazine right now (November 2007) and in the article (Raising Heaven) it says, "They were expecting to find that the rate of expansion has slowed over the eons... instead, the astronomers were astonished to find that cosmic expansion is not slowing down at all: it is speeding up... it's as if a ball, thrown into the air, at first slowed, but then sped up and simply flew away. No natural force on earth can do such a thing - and none in the known universe could do such a thing.

The movie is more recent than the magazine. What's the deal.
It's suspected that what's termed "Dark Energy" is causing the space of the universe to expand. It's thought that early on following the Big Bang, that Gravity (as a fundamental force) was probably the dominate force. If gravity had been able to continue as it had, the universe would eventually slow down and collapse in on itself. For some reason (which is unknown) Dark Energy gained an upper hand over pull of Gravity. As the the space in the early universe grew larger, Dark Energy has the ability of creating new space which in turn causes Dark Energy to become stronger overpowering Gravity, and the space of the universe continues to increase even more. And the stronger Dark Energy becomes, the faster the rate of expansion becomes.

Distant galaxies that are moving away from us are seen as red-shifted. The more red-shifted a galaxy is, the faster it's moving away. However, it isn't that the galaxies themselves are moving away at such great speeds, but rather that space itself is expanding causing greater distance between those galaxies and us.

It's also worth keeping in mind that the greater the distance in space between objects in the universe are from us, the farther back in time those objects are. It also helps to understand that we can only see as far as what is called the Particle Horizon. In other words, any galaxies that cross beyond the Particle Horizon will never be seen because the light emitted from such objects are too far to ever reach us. and that's especially true as the expansion of space continues.

We are seeing is that some of those objects are around 13 billion years old. The farther away from us an object is, the farther back in time it is. That means what we are looking at is how they were 13 billion years ago. Since they were so greatly red-shifted 13 billion years ago (because that's how they look to us now), then they have probably already crossed the Particle Horizon billions of years ago because some of these distant objects appear to be moving away faster than the speed of light. Eventually, some of them will disappear from view.

It's been said that Dark Energy is just a general term used for a phenomenon we don't really uniderstand yet. Dark Energy is a hypothesis. It's possible there could be some other explanation for the accelerated expansion of space, but for now, Dark Energy seems to fit. Dark Energy might be a property of space itself.

Just a note about Gravity and Dark Energy. Gravity is an attractive force that pulls or compresses matter together. It's what sculpts and shapes things in the universe. Dark Energy is repulsive, causing space to expand. It isn't really known if it's pure energy or if it's an unknown force. For what it's worth, Dark Energy is not the same thing as Dark Matter.

Finally, both the guy (Brain Cox?) in Wonders of the Universe and the National Geographic are correct. If the universe continues expanding, then it will eventually die out because entropy would reach a maximum and virtually everything, including black holes, would eventually vaporize out of existence. That said, space itself could continue to expand indefinitely, but if its just empty with nothing in it, then there really wouldn't be much to call a "Universe", would there?

I'm inclined to think there may have been some sort of conditions that pre-existed the universe. If the space of the universe continues expanding, even at an increasing rate of acceleration, space itself would probably be stretched so thin that it essentially blends in with such pre-eisting conditions. In effect, the space of the universe would eventually cease to exist in any meaningful sense.

Does any of that help describe "What's the deal"?
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Old 03-17-2012, 08:50 AM
 
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NB

Wouldn't cosmic inflation had been the force that kept gravity in check just after the Big Bang and not dark energy?
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Old 03-17-2012, 02:31 PM
 
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Originally Posted by 6 Foot 3 View Post
NB

Wouldn't cosmic inflation had been the force that kept gravity in check just after the Big Bang and not dark energy?
It's hard to know exactly what took place during the period of inflation. It's worth noting that Gravity is a fundamental force. Dark Energy is still an unknown, but is a term that helps explain the expansion of space. It could be that what's called "Dark Energy" might be an exotic and as yet unknown force that causes space to expand, but no one is really certain exactly what it is. It's also possible Dark Energy might just be a property of the 'fabric' of space-time.

Following the brief period of Inflation, which would have been many times faster than the speed of light, the expansion slowed down as temperatures cooled. Current thought is that the rate of the expansion of space has accelerated rather than continuing to slow down. Exactly why space slowed down then began to accelerate again, is something I don't understand. It seems counterintuitive. It would seem reasonable that the expansion of space should be slowing down.

One thing that strikes my view is that the determination about the acceleration of space is more pronounced by the extreme red-shifting of light from very distant objects. Not only are these objects extremely distant in space from us, but they are also extremely distant in time from us. In other words, we're looking at objects as they were billions of years ago, which also means these objects formed closer to Big Bang. Because these objects are so old, and so greatly red-shifted, at this moment in time (relative to us as observers) they're probably far beyond the particle horizon of the observable universe. In other words, if you could instantly get there from here, they'd be long passed the particle horizon by the time you got to where you thought it was supposed to be because space was expanding faster than the speed of light billions of years ago. We only see them because it's taken billions of years for the light we now see to reach us.

As we look at objects closer to us, we don't readily see red-shifting of objects as extreme as we do with these distant objects. In other words, the space we occupy is probably expanding at the same general rate as the distant objects, not counting fluctuations within the universe. The fluctuations as seen in the cosmic microwave background is looking at fluctuations in temperature and density. There might be fluctuations in space as well, but may be beyond our ability to observe. The problem is that we don't really know how large the universe really is beyond the particle horizon. There are some estimates, but those estimates are based on what we consider to be the age of the universe which is basically out to the particle horizon.

If Gravity had not played such an important role in the evolution of the universe, then it's not likely much of anything would exist in it. There might be particles, but no stars, planets and galaxies. Probably no atoms either. If Gravity had been much stronger, then the universe would have most likely collapsed in on itself shortly after the Big Bang.

As it turned out, the universe continued expanding which might have weakened the force of Gravity, thus allowing the expansion to continue. While Gravity is considered to be the weakest of the fudamental forces, that doesn't mean Gravity itself is weak, especially when we take into account the effect it still has on shaping the universe at very large scales. At some point in the far distant future though, the expansion of space will likely be so vast that the effect of gravity will eventually lose its effect on almost everything.

Again, it isn't certain that Dark Energy even exists. It could just be how we perceive it. Like I said, it might simply be a property of space-time in the universe. Or it could be that it does exist, but is so exotic that we don't understand it at all.

What's difficult to understand is that the brief inflation would have increased space at a rate much faster than light speed, then of course slow down which cooled space and allowed for matter to begin forming gas, stars, and galaxies, but at some point the expansion began to speed up again. The best I can come up with is that if Dark Energy exists, and is responsible for creating new space, then as space increases, Dark Energy becomes stronger and continues creating more new space at an ever-increasing rate.

Sorry to have taken the long way around to your question, but I think it might help to set the scenes and provide some framework. With regard to your question, yes, the initial inflation probably was so strong that Gravity was unable to keep things compressed together. Initally, Dark Energy was probably somewhat weaker, but as more space increased, Dark Energy became stronger and over powered the effects of Gravity, at least on a cosmological scale.

We have to keep in mind that we don't really know exactly what the origins of the universe are or why the Big Bang banged. There are numerous other scenarios, some plausible, some not so much. The Big Bang seems to be the most widely accepted. As it is, it's a difficult task just to make an inventory of what's in the universe. We continue to make more new discoveries that we couldn't previously imagine. I suspect it'll be like that for quite a while in the future. To use an often stated phrase, "The Universe is a REALLY BIG place."
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Old 03-19-2012, 09:07 AM
 
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Originally Posted by NightBazaar View Post
If Gravity had not played such an important role in the evolution of the universe, then it's not likely much of anything would exist in it. There might be particles, but no stars, planets and galaxies. Probably no atoms either.
As for atoms isn't the Strong Nuclear Force the force that creates or keeps atoms together and not gravity as gravity doesn't have any influence in the sub atomic/quantum world from my understanding.
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Old 03-19-2012, 08:04 PM
 
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Originally Posted by 6 Foot 3 View Post
As for atoms isn't the Strong Nuclear Force the force that creates or keeps atoms together and not gravity as gravity doesn't have any influence in the sub atomic/quantum world from my understanding.
You're right about the Strong Nuclear Force. Thanks for bringing that up. I need to clarify my point better. What I was getting at is that if there was no Gravity, then nothing would have had any shape or structure in the universe. If Gravity had turned out stronger than it is, stars could have formed, but they would've quickly burned out. Too weak, and there'd have been no star formation because there would have been no gravitational attraction of matter. We can't say Gravity has no influence at the subatomic or quantum scales though. Possible examples: micro black holes, quantum gravity.

I think what you're referring to about the strong nuclear force and what holds atoms together, are the messenger particles called gluons. The unknown question is whether all the fundamental forces emerged at once following the Big Bang. If they emerged somewhat separately, then I would think the extreme compressive state of energy was so intense that it really wouldn't matter if gluons were present or not. Gluons wouldn't have been able to do their job until there was at least a little wiggle room for particles to start combining.

Keep in mind that for a time following the instant of the Big Bang, there weren't any atoms. Before the first hydrogen atoms formed, even before particles like protons and electrons emerged, there would've only been stuff like quarks forming. To go much deeper than quarks, as to what matter and everything else is made of, we'd have to start getting into Grand Unified Theories (GUT) such as String Theories.

It wasn't until the space created by the Big Bang reached a point during inflation that there was more room for the emerging particles to move around. Particles would have been pretty much of an equal mix of positive matter and anti-matter. That's not to underestimate the other forces, but Gravity may have been the dominate force very early on. If you think of the singularity as similar to that of a black hole (although far more extreme), then Gravity would play a major role in the formation of the universe. It still does, but unlike the other forces, Gravity became weaker as the universe expanded. The big difference being that the Big Bang was so intense that space was being created at an exponental rate that Gravity was unable to maintain the full strength of its grip, in effect causing Gravity to weaken. It's suspected Dark Energy might be what's causing space to expand. There could be a connection. As Dark Energy is expanding the space of the universe be creating it, and growing stronger as more space emerges, that may be a reason why Gravity is so weak in comparison to the other three fundamental forces. There are also thoughts that gravity (gravitons, if they exist) could be leaking out of the universe, perhaps through quantum tunneling (hypothetical wormholes).

As a note, Gravity has an unlimited range, but it's strength is relative by the distance between two objects of mass (and energy). The closer the objects, the greater the gravitational strength between them. I suppose technically, Earth's gravity has an effect on the Andromeda galaxy, although extremely weak. That's because the Earth contributes to the overall mass of the Milky Way galaxy. Regardless, the gravitational attraction of every object with mass has an effect on every other object of mass. Because Gravity is everywhere in the universe, it might be an integrated part of space and time of the universe. The Strong Nuclear force, like the Weak Nuclear force, is limited to subatomic distances.

Gravity may have been much stronger than it is now. The reason is that when the universe was much smaller, and whatever was in it was much closer, the gravitational strength seems like it would have been much stronger. There have been some suggestions that Gravity (big G) was much stronger and may have been the first of the fundamental forces to emerge. Over time, Gravity has become weaker compared to the electromagnetic and strong nuclear force. We can't say gravity does not exist at the quantum scale. Loop quantum gravity might very well exist, which might help explain something like micro black holes (quantum gravity black holes). If gravitons exist (still unknown) and are the carriers of Gravity, it may be that gravitons can somehow leak out of the universe through microscopic wormholes (hypothetical) existing at the quantum scale which may open and close all the time. That would also lend support as to why Gravity is weaker than the other forces.

The thing is that it's hard to compare the force of Gravity with the other fundamental forces, because Gravity is so different from the others. Although Gravity is an attractive force, it doesn't have a positive or negative charge. It's a real oddball.

Please correct me if I'm wrong or overlooking something.

The Four Fundamental Forces

The Mystery of Gravity : The Astronomy Cafe : Dr. Sten Odenwald

Theory of everything - Wikipedia, the free encyclopedia

Quantum gravity - Wikipedia, the free encyclopedia
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Old 03-19-2012, 09:18 PM
 
Location: Texas
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I hesitate to believe in micro black holes. I just can't put my finger on why -- pro or con. Could this fall into the realm of "maybe, maybe not?" Seems to me, there would have to be a certain amount of gravity for even a micro second.
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Old 03-19-2012, 11:28 PM
 
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Originally Posted by Brian.Pearson View Post
I hesitate to believe in micro black holes. I just can't put my finger on why -- pro or con. Could this fall into the realm of "maybe, maybe not?" Seems to me, there would have to be a certain amount of gravity for even a micro second.
Yes, currently micro black holes do "fall" (LOL) into the "maybe, maybe not" realm, as is quantum gravity. So are gravitons, the Higgs boson, multiverse, extra dimensions, and a host of other things. But they are predicted as mathematically possible by theoretical physicists. They haven't been confirmed to exist, but they can't be said they don't exist. They are "possible", which is what I had indicated. The point I was making is that we can't conclusively say that Gravity doesn't have any influence in the subatomic/quantum world. It has been hoped to see evidence of a micro black hole in some of the particle collisions at the LHC, which brought out a few folks from the doomsday brigade before the switch was turned on for the first time.

At the present time, none have been detected. This could suggest that they might not exist, or they might be too small to detect any effects, or conditions haven't been sufficient enough to generate one from the collisions yet, or they're a lot more elusive than thought. Frankly, I have no idea if they exist or not.

I agree with you that there'd have to be a certain amount of gravity. Okay... was there more to add to that thought? Or were you thinking that gravity might not exist at such small scales where micro black holes are thought could potentially form?
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Old 03-19-2012, 11:59 PM
 
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Originally Posted by Brian.Pearson View Post
I hesitate to believe in micro black holes. I just can't put my finger on why -- pro or con. Could this fall into the realm of "maybe, maybe not?" Seems to me, there would have to be a certain amount of gravity for even a micro second.
Micro black holes could only exist for a incredibly tiny amount of time before they evaporated.
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Old 03-20-2012, 07:59 AM
 
Location: Texas
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It could happen to one of us, maybe?
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