purintjp

Why does it have to be gravity to cause the contraction ? Since it expanded due to energy released, could not a reduction in energy begin to slow and maybe contract spacetime until gravitation masses became close enough to start to pull everything back together to cause a big crunch ? I tend to accept this possiblity more than the original big bang expansion from a singularity. I just don't like the something from nothing explanations, although a big bang from a big crunch still does not explain where everything came from.

Adam, you are not the only one who thinks about this kind of stuff. I posted the following some time back. Just how empty is space, really. There are all the various radiation spectra and things like neutrinos and other exotic particles rushing through space pretty much everywhere. Not to mention stuff we probably can't even detect. Maybe the idea of 'nothing' does not even exist. I think that the proof of nothing is tied to the proof of infinity. Is not the best definition of infinity as 'something' divided by 'nothing' ? They both could be just pure mathematical concepts. I know scientists are dead set on using mathematics to describe everything but I doubt they will. I often wonder if mathematics is not a victim of it's own precision. Everything seems to break down around 0 and infinity. What is it that is exactly equal that is larger than quantum level ? Are we 100% sure that even quantum level stuff is equal down to the most infinite detail ?

So based on what you are telling me, it is certain that given what we currently know about expansion and cluster formation that we can probably be sure that at some point in time Andromeda was nudged into our path (or vice-versa) or that the velocity was altered at some point ? If so, could it have been collisions that it had with other smaller galaxies ?

Thank you Martin for the reply. I had not heard of the measuring to the CMB until this very thread. What you replied goes to the very heart of my original thread post. If you assumed that the two galaxies are 12 billion years old and ran the scenario backwards the distance between the galaxies would have been 2.5M lt/yrs + 5M lt/yrs to equal 7.5 M lt/yrs. I assume that the Hubble constant would have been different 12 Billion yrs. ago but the math is probably beyond me. Seems like there might be a chink in the armor of something.

Good stuff guys!! I hadn't ever heard about the "Great Attractor". Can someone provide a well-respected link to learn about it. Also, I was wondering how far away would we have to be from Andromeda before gravity would be overcome and the expansion of space would take over. (Approx.- I'm assuming that no other gravitational force would interfere)

Thank you Martin for your always concise explanations and time. I hadn't considered the possiblility or them orbiting each other. That being said I did some quick calculations and using a speed of 130 km/s being the total approach speed giving a speed of about .0004*c they would only have traveled about 4,000,000 lt/yrs in 10 billion years. I know that's a rough estimate but doesn't seem to give enough time for many orbits. Am I missing something ?

As I understand it, the galaxies moving towards us are in our local galactic cluster. Since Andromeda is moving towards us at the current time I was wondering if using the shrinking universe analogy that is used to speculate that most galaxies that are moving away from us at one time were much closer to us at creation would suggest that Andromeda was farther away from us at our creation times. It would seem that this would have to be true or Andromeda would have already collided with us during expansion. Would the distances between now and then jibe with the rate at which it is coming towards us without being too far away at creation to be affected by gravitational forces ? It would seem that it has been coming towards us for an awfully long time to still be 1 million light years away.

I don't particularly like the balloon analogy either. I don't think that the hypersphere is really all that hard visualize. As long as you consider the balloon model expanding thru time and space creating a sort of pseudo- space/time representation you pretty much have the hyper-sphere. It is also a very useful representation of how light has to travel from the early universe to finally reach us. A cross-section of the hypersphere shows this quite well. All that being said, I still have a problem with the traditional BBT. It seems more likely to me that the universe is cyclical in nature and expands till energy is mostly gone and there are nothing but heavy elements left which will combine in a relatively large and no where near infinitely small density and space and will then go critical after breaking down into the universal building blocks. Still a big bang but without the faster than light expansion. Trying to understand what started it all is no doubt a futile effort. I just don't understand why so many people cling to theories that predict seemingly outlandish results. I guess everybody is entitled to his opinion.

I was only positing a spherical model for ease of calculation. Without some sort of explosive impetus why would space expand ? I wasn't referring to light escaping the universe, I was referring to the release of light from the singularity into space as it began to expand. As far as light being held back by dense matter, it would seem to me if I were able to stand outside that singularity I would be able to see something that hot and dense unless it had black hole charactistics. Is that what you are claiming ? If not; What about light at the extreme edge of this singularity, what would be holding it back ? I'm assuming that the universe never got smaller than 377,000 LYrs.

I was thinking about this and I was wondering if it were possible that the universe were cyclic and that it had collapsed to the point that BBT theorists posit had occured around 380,000 LYrs just before light is able to escape and then big-banged into existance. I don't have the math experience to calculate what the density would have been at that point but I would be curious if anybody has ever calculated that based on what the believed density is today at 13.7 BLYrs to see if it might make sense. (Assuming a spherical universe). I wonder if there would be any correlation to the density required to create a black hole and the calculated pre-BB density. It is interesting that at those points light could escape neither of those. Maybe all the basic building blocks of matter have always been here and were not created by the expansion of a point singularity as a big bang from nothing.

It is my belief that we will never be able to integrate the universe through mathematics. It is a victim of its own precision. Everything seems to break down when it approaches zero or infinity. There seem to be levels of what I like to call relative infinity or relative zero. We are insulated from these areas and for good reason. Relative infinity is easily less than 1000 light years and any attempt to derive anything of practical value is probably a waste of time. Our best bet is the near practical zero of Quantum mechanics which may offer some useful practical applications for energy production or other scientific use. The single most important thing for science to discover is whether infinity or nothing (zero) truly exists in our relatively closed system. Only then will we understand the unfathomable universe.

I guess I was trying to make a point that it is possible to travel away from something faster than the speed of light if you are being "carried" rather then accelerating. It is pretty hard to wrap your mind around the difference. As far as being closer to the Milky Way, I believe that practical infinity is easily less than a 1000 light years away and although I love all the gee-whiz stuff that comes out of scientific research I think it is probably a colossal waste of time to ascribe any sort of practical application or use in today's world. I think we would be better served to allocate more money and time to Quantum Research as we are far more likely to reap any real world benefits. Of course, I am just and idiot without scientific credentials.

I was under the impression that far distant galaxies are a lot farther away than can be explained by the age of the universe. We are seeing only the light from the very beginning of the universe of the galaxies farthest away. Who knows exactly where they are now. If you look at my post in Cosmology and Astronomy 'Big Bang Paradox' you will see Martin trying to explain it to me. Perhaps I misunderstood. If so, mea culpa.

And yet most scientists believe that entire galaxies can travel away faster then light as long as they are "carried" along by the expansion of space/time. It seems we just need something to "carry" us along to achieve the same result. Who knows what that might be.

Thanks for the info. Here in Los Angeles we have some difficult atmospheric and illumination issues. I only had binoculars but it almost appeared as a comet.