Gravity and confusion.

[Isaac]

So I got into this heated argument with a friend of mine who says the universe will not collapse into its self.

My argument: If space, time, and gravity are infinite then all matter will collapse into its self, eventually. Regardless of what it's all doing right now.

How can it work any other way?!?

[Grendel]

http://en.wikipedia.org/wiki/Ultimate_f ... f_universe

[Isaac]

Thank you Grendel.

Theoretically, the oscillating universe could not be reconciled with the second law of thermodynamics: entropy would build up from oscillation to oscillation and cause heat death. Other measurements suggested the universe is not closed. These arguments caused cosmologists to abandon the oscillating universe model.

So I wanted to know about this entropy thing:

The second law of thermodynamics is an expression of the universal principle of entropy.........entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium...........

The rest was beyond me. But I understand that they're trying to say that an "oscillating" universe isn't long term. If it was oscillating, matter would be random as possible per oscillation until it mixes too evenly and stops. That still sounds wrong! What about gravity!? No matter how much universe mud you have, the gravity of an object will always be pulling.
Heat loss? Gravity is a heat generator of infinite power! And as it builds it will generate pressure like the tensioning of a bow.

[Foil]

Regarding your original question:

I's a common mistake to think that because gravity is always working at any distance, that everything must eventually be pulled back toward the source. I had the same discussion with my brother a couple of years ago.

Think about the concept of 'escape velocity'. Although gravity works at infinite distances, its effect diminishes quickly as the distance increases. Depending on the initial velocity, the gravitational effect may or may not be enough to ever pull the object back in. It's really a measure of potential energy vs. kinetic energy.

This is (very loosely) analogous to the expansion of our universe. Depending on the energy and matter, and rate of expansion, the universe may or may not ever be \"pulled back together\". It's still being debated (I still recall some arguments in an undergrad Physics course about the 'Density Parameter' in the link above), although there have been some developments since I last studied it.

[Krom]

The universe is accelerating its expansion, like it is still in the process of exploding. Last thing I read or saw on it they still couldn't explain why it was accelerating so they called it dark energy, I don't know if that has changed now.

The theory as I understand it currently says that the universe will expand forever till everything decays and the universe is filled entirely with nothing but energy (even black holes evaporate into nothing given enough time) at which point the laws of physics as we understand them collapse.

One of the theories I heard for why the laws of physics collapse at that point says it is because without any matter in the universe many of the dimensions collapse. Without matter, concepts like mass, volume and time don't exist anymore, and the dimensions governing them all fold into a single point dimension. Granted this is only our current guess of the laws of physics, everything we know depends on matter as a point of reference and it is a serious mind twister to try and conceptualize the universe without the 3 (or 4) dimensions we live our day to day lives in.

[NUMBERZero]

So what you are saying, Krom, is that without matter, nothing will matter. har har har

I may be going off on another subject here, but I was reading a Discover magazine that said that the universe is moving towards some \"ancient object\" beyond...What was it? Our visual range or beyond some special machine that can see way beyond to the \"edge\" of the universe where it is still expanding. Real question is, do they really believe that some ancient object is out there pulling everything towards it? In order to do that to everything, it needs to be, say, the size of a basket ball with the universe being a single atom. Maybe a little bigger. And what is out there for them to judge that the universe IS moving to that one point.
What would you say that object is? Some gigantic Death Star/Pac-Man just eating the universe? The world may never know.

It's off topic, but I find it all interesting.

[Isaac]

Krom and foil... I read your comments. give me a few days to wrap my caveman brain around that.

[Krom]

I don't know about anything outside the observable universe, but there was a interesting bit of info I read about in a book like 15 years ago: Our galaxy, and many other galaxies are in fact all the equivalent of individual stars in another super galaxy. The more you read up on this stuff, the smaller you feel, but its still cool anyway.

http://en.wikipedia.org/wiki/Great_Attractor

http://en.wikipedia.org/wiki/Shapley_Supercluster

[Lothar]

http://www.ifa.hawaii.edu/info/press-re ... vski-1-06/
http://www.atlasoftheuniverse.com/superc/shapley.html

I wouldn't say our galaxy is the equivalent of individual stars in a super-galaxy, but there is a cluster of at least 135 galaxies out there with total mass about 10,000 times that of the Milky Way.

[SilverFJ]

Isn't it some kind of theory that solar systems are just atoms, the sun is the nucleus and the planets are protons and electrons? To a layman such as myself that makes more sense that any of this physics.

[Lothar]

Isn't it some kind of theory that solar systems are just atoms, the sun is the nucleus and the planets are protons and electrons?

Strangely, I was just reading about a (fairly nutball) theory about the sun being principally electric rather than fusion+gravity; it's quite thoroughly debunked here.

The planets are not electrically charged like electrons, nor is the sun charged like a proton-neutron mix. The resemblance of star systems to atoms is superficial.

When it comes to the much larger "super galaxies" Krom mentioned, they're not really as large as his initial statement implies. For our galaxy to be equivalent to an "individual star" in a super-galaxy, that super-galaxy would have to contain about 100,000,000,000 times the mass of the Milky Way. That means the Shapley Supercluster is still about 10,000,000 times too small.

[SilverFJ]

The planets are not electrically charged like electrons, nor is the sun charged like a proton-neutron mix. The resemblance of star systems to atoms is superficial.

Okay, once again, I'm a layman for this, but how can you make that call without the means of measurement we can apply to atoms? We don't have a super microscope the size of the galaxy to look at our solar system with.

I just remember some kind of cartoon I saw when I was really little, where a guy was cracking open an egg, but while he was doing it, the world was shaking and cracking around him, and he looked in the egg and there he was, looking up a him, and he looked up, and there was a guy cracking his egg... That makes so much sense to me, call me crazy...

[SilverFJ]

Ok, so it's different than I remembered it, but it's still the same idea...

http://retrojunk.com/details_commercial/3608/

[Lothar]

but how can you make that call without the means of measurement we can apply to atoms? We don't have a super microscope the size of the galaxy to look at our solar system with.

We have measurements of both. They're nowhere close to the same. The sun and planets aren't electrically charged; it's gravity, not electricity, that holds us in orbit. The resemblance is superficial.

Spend 10 minutes with google or wikipedia.

[Isaac]

So we have a universe with matter that's exponentially spreading apart. Some of it almost travelling at the speed of light. This is also something that's suppose to prove that the universe isn't oscillating. I've been Googling everywhere on this subject. Very little makes any sense to me. But I have some theories that do make sense:
I understand what orbiting and sling shooting is. And from my understanding it happens a lot in space. In fact it seems like everything is doing one or the other. Everything that slingshots into our cluster of galaxies will be influenced by many other forces. Things that slingshot out will go as fast as they were originally shot at forever with little or no influence. Overall, with gravity shooting things faster than they were originally travelling, this would cause the universe to expand faster at an exponential rate.

[SilverFJ]

Speculation, speculation.
None of this is fact, proven.

Ideas from looking through the eye of a needle with our few, miniscule five senses.

The physics we know only apply to earth, the rest is just guessing.

I'm gunna stick with my giant atom theory, it has just as much creedence.

[Lothar]

The physics we know only apply to earth, the rest is just guessing.

Strictly speaking, nothing is proven even on Earth. That's not how science works; it doesn't prove anything, it just generates theories that consistently correctly predict future behavior. (And, strictly speaking, you don't know if physics actually apply outside the limits of your own personal observation. I could be levitating in front of my computer, telepathically manipulating electrons to produce this post, for all you know.)

We have spacecraft orbiting Sol, Luna, and Mars, sending back various forms of data. We've landed spacecraft on Luna and Mars, and even had people walk around on the Lunar surface. The physics we know seem to apply there just as well as to Earth. The observations we've made of the rest of the universe (light, x-rays, gravity, etc.) seem consistent with the laws of physics.

The measurements we have are pretty darn good. The "giant atom" theory simply doesn't match them. It doesn't have any credence whatsoever, because it doesn't fit the actual data we have. (Again, that's how science works -- you can introduce new ideas, but they have to fit the data; if they don't, they're garbage.)

[Isaac]

The observations we've made of the rest of the universe (light, x-rays, gravity, etc.) seem consistent with the laws of physics.

Don't forget very large objects.

[Spidey]

I think the better analogy to atoms would be galaxies, not solar systems, and the fact that the attraction forces are not the same makes no difference…because it is only an anology.

BTW all mass (atoms & above) has an electric charge, even if it’s a neutral one.