Assumption: the majority of galaxies have been located.
Assumption: The majority of Galaxies have had their mass determined.
Assumption: All Galaxies that have been observed have had their velocity measured by their red-shift
Assumption: Within a period of about 100 years we have detailed knowledge of the movements of galaxies nearby based on their measurable movement.
Conclusion: Current physics, with the aid of computers, can develop substantially accurate maps of the current location of Galaxies by extrapolation.
I want to ask, what is wrong with my individual assumptions, and my conclusion. I suspect The existance of 'Dark Matter" and the inexplicable acceleration of galactic expansion will be reason enough to invalidate the conclusion, but would like others to give me the right information about anything I have gotten wrong.
My thanks, AllFreedomUnlessDefyingScience
When you are the only sane person in the room, everyone else says you are crazy. Have you ever noticed that the world is just one big room?
Assumption: the majority of galaxies have been located.
The “majority” of galaxies have certainly not been located. The deeper we look, the more we find. We don’t know how large the universe is beyond the 27-ish billion l.y. sphere we can observe. It might go 2 feet past that, or billions of l.y.'s more.
Assumption: The majority of Galaxies have had their mass determined.
The problem is that their observable mass doesn’t match how they hang together. They behave as if they were much more massive, but we can’t find that mass. Hence the “dark matter.” So have we really determined their mass?
Assumption: All Galaxies that have been observed have had their velocity measured by their red-shift
OK, as far as I know.
Assumption: Within a period of about 100 years we have detailed knowledge of the movements of galaxies nearby based on their measurable movement.
Again, OK.
Conclusion: Current physics, with the aid of computers, can develop substantially accurate maps of the current location of Galaxies by extrapolation.
You mean the current location of galaxies we have not yet observed? If so, that’s unlikely. They’re not laid out in a grid pattern or anything. Our best guess is that the superclusters of galaxies are spread out in thin layers around great voids, like a foam. At the ultra-macro level, there is regularity there, but at the “micro” level (larger than supercluster) there is still tremendous randomness.
So there could in theory be clusters of galaxies a couple septuagintillion light years away from our location for all we know? The ~ 15 billion light year radius is strictly a limitation on observability (i.e, light from things farther away than that hasn’t had time enough since Bang! to get here), and has nothing to do with how large the universe itself actually is?
This is exactly the kind of feedback I was looking for to give me a better grasp of astrophysics and the current state of the universe.
About the Assumption that the majority of Galaxies have been located and that 27 Billion light year sphere; Assuming that the universe and matter in it didn’t exist before the big bang, doesn’t that observable distance give us data on all matter since shortly after the big bang?
Concerning the assumption that we have a good idea of the mass dispersal of the universe; Haven’t the 100+ years of astronomy given us data that has begun to and will gradually reveal more about the dispersal of ‘dark matter’ in the universe by inference from the movement of the visible matter like galaxies giving us at least the potential to someday map the interactions of galaxies in the universe?
Concerning my conclusion that we could develop an accurate model (I probably shouldn’t have said map) that places observable galaxies at the position they occupied at the point in time where the light we observe from them is visible Could we not develop a model for the location of matter and Galaxies near the beginning of the universe and possibly extrapolate from there as to where other galaxies are as the universe aged, potentially (at least some day) giving us an up-to date extrapolated model of the current position of galaxies in the universe?
I appreciate all feedback. I’m not advocating a position here, but looking for someone to help raise my knowledge of the universe and astrophysics by pointing out how these assumptions are wrong, and letting me know what the scientifically accepted view of the universe tells us about the conclusion I drew, and if there is a clear conclusion to draw that I haven’t touched on.
My thanks for all assistance,
AllFreedomUnlessDefyingScience
P.S. Does my signature quote appear twice? I can’t see it myself and wonder if sigs are invisible to the poster, or I need to fiddle with my settings more to make my signature appear. Thanks
If you are the only sane person in the room, everyone else says you are crazy. Have you ever noticed that the world is just one big room?
Measuring the red shift will only give us the radial component of the galaxy’s velocity. We’d need to know the transverse component as well to predict future locations. I don’t know if we know those.
No, not by a long shot. It’s unclear how much of the total universe is visible to us. We may only be looking at a vanishingly small fraction of the total number of galaxies in existence.
The farther away something is, the longer its light takes to reach us. If a galaxy is farther away in light years than the current age of the universe, it’s light won’t have had time to reach us yet. Now, if the universe WASN’T expanding then every year a few galaxies would come into view at the edge of the visible universe. But since it IS expanding and the rate of expansion is accelerating we’re never going to see more than the tiny fraction we currently see and we’ll probably eventually see less.
As OldGuy points out, for distant galaxies we only have information about the velocity vector directly toward or away from us. We don’t have any information about their drift from side to side. However for distant galaxies their apparent motion from the expansion of the universe almost completely swamps any other velocity they may have, so you can roughly approximate their “current” positions relative to us by extrapolation.
To put this into some perspective, the Hubble Ultra-Deep Field. They took the Hubble and just stared for weeks on end at a single spot on the sky that appeared to be empty. This image is of an area of the sky about the same as the size of a grain of sand held at arm’s length, and they’ve only taken images of about three such specks. Almost every one of the spots of light in that image is an entire galaxy (the three spots that have cross-shaped rays coming out from them are foreground stars, but everything else is a galaxy). And this from a patch of sky that, without a weeks-long exposure, appears to be empty: Everywhere you look in the sky, you’d see something similar.
Yes. We’re in a dark room, holding up our lighter. We can only see the sphere of light immediately around us. We have no idea of knowing for sure how big the room is.
I think that, of the galaxies that have been observed, a negligible fraction have had their distances or radial velocities measured.
Also, we are talking astronomy here, not astrophysics. If you want to know how stellar atmospheres evolve, or what quasars are doing, you are interested in astrophysics, but figuring out where all the galaxies are would be a problem in astronomy.
If the Humanity doesn’t commit racial suicide (something I gravely doubt we will avoid) after 1000+ years of observation with increasingly better imaging would we be able to determine the radial movements of galaxies, estimate the concentrations of Dark Matter and construct a universal model such as the one I have talked about? Or will it be impossible even then?
Could you explain something to me? If the universe is approximately 15 billion years old, and we can see 15 billion light years, doesn’t that mean we can see either where Galaxies are now (if they are close to us) or where the matter that formed galaxies and stars was soon after the big bang? What matter would be unnacounted for based on this view, assuming you could eventuallly build up enough data to map the concentrations of Dark Matter? Wouldn’t anything beyond that point require matter to have existed before the Big Bang (I just have to add, I much prefer the term H.S.K or Horrendous Space Kablooie, as Calvin pointed out Big Bang just sounds so underwhelming)?
Oh, and I love the links you guys sent, both of them are fantastic and the one about scale of stars is particularly awesome.
I’m not talking about infinity I don’t think, while the size of the universe itself may be infinite, at least the material released from the Big Bang is contained in a finite area isn’t it?
It’s my assumption that any model of the state of the universe will not just require astronomy, but some heavy duty astrophysics to model the interactions of the stars and galaxies and possibly the Dark Matter in the universe in addition to simple Newtonian physics and astronomical observation. Am I that far off base?
All astronomy is astrophysics. I don’t understand what distinction you’re drawing.
You also reference dark matter, but you haven’t mentioned dark energy. Unless you’re mixing up the two terms, dark matter is mostly relevant to individual galaxies and their structure, but dark energy stretches the entire universe.
The Big Bang went through an expansionary phase where space itself grew at a rate faster than the speed of light*. This is often pictured as putting dots on the outside of a balloon and then inflating it… while the dots don’t move around on the surface, the changes in the size of the surface make them farther apart. Light going from one galaxy to another does have to cross the whole surface of the balloon, and so two objects that were once very close together may be unable to see each now that the space in between has inflated so much.
And expansion hasn’t stopped. It’s just slower now than it was in the expansionary phase.
No. Very soon after the Big Bang the universe went through an inflationary period where the rate of expansion was far, far higher than it is now. During this period locations that were initially close to each other receded from each other at much, much faster than the speed of light. (This doesn’t violate relativity because they weren’t actually *moving *relative to each other. The space between them was merely stretching.) The result is that that a large part of the universe is almost certainly outside the distance that light has been able to travel since the Big Bang. It’s permanently invisible to us.
