Discussion in 'Astronomy, Exobiology, & Cosmology' started by S.A.M., May 9, 2007.
more Rhetoric? why do you even bother to post?
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Not necessarily. Parameters merely allow for our lack of knowledge at the present time. As new data comes in, we tighten up on the possible values of the parameters. In other words, parameters help to quantify what we do not yet know for sure.
That's what science is all about.
Technically, dark matter and energy are not variables. They are attempts at explanations for observations that put certain values on variables (parameters). These explanations may ultimately turn out to be wrong, but that won't change the known data. We'll just need another explanation.
Again, that's what science is all about.
As I said, the universe has no centre in space. When we look out far enough we can see back to a time not long after the big bang, but the bang happened everywhere, not at some point in space.
The microwave background radiation is from the big bang. It is what we see when we look to the edge of the observable universe.
We don't, but we know for sure there are at least 4.
Sloppy wording in a press release. They mean the "edge" of the visible universe - that is, the furthest back in time we can look.
There is no centre.
It means that the average distances between galaxies are getting larger at an ever-increasing rate.
Length contraction is a result of relative motion. When you stop moving, length contraction goes away. The expansion of the universe doesn't go away. All observers agree the universe is expanding, regardless of their motion.
I just use the standard general relativistic definitions of spacetime coordinates etc.
Do you know of a better way of defining space?
Well, you're the expert. You're qualified to evaluate the status of cosmology, I'm sure.
Uh, OK. Now which objects can I look at to confirm this prediction? Not the ones moving at great relative speeds due to the expansion of the universe, I presume.
So regardless of the observer's motion relative to a distant object, the distance won't appear to contract and the object will always appear to be moving away from the observer?? I thought you just said length contraction is a result of relative motion?
Sorry James, but I just couldn't help it! Please Register or Log in to view the hidden image!
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The impression I get from reading this thread is that nobody except James R has a grip at this subject. I think some reading on basic concepts of cosmology, such as the relativity theory and metric expansion of space would substantially improve the quality of this discussion.
So maybe you can tell us what the 95% of the missing mass of the universe is? the arxivs are full of papers telling us that scientists do not know what it is, and that every proposed test is all ways just beyond reach.
So Varda sit down and tell us what is known about cosmology, the parts
that are testable today.
Please, don't be offended fishtail. It is just very difficult to discuss things that scientists are in doubt about, when even things that scientists are mostly certain about are being so blatantly missunderstood. I don't thing we should skip to more complex subjects when the basics are still going over people's heads.
Ouch...runs away with tail between his legs...
Really this is a subject somewhat open to a lot of interpretation. We have such a small window of "time" to view the "universe".
Well, yes, they are interpretations of our data. But basically, we are measuring two things which we identify as "dark matter" and "dark energy".
Wouldn't the brane theory make more sense, then?
James R knows his shit, but he doesn't try to test the theory and play with it. I could tell you everything I know about cosmology and it would sound not much different then what James R has to say. But I much rather challenge our interpretations of the data, as opposed to simply restating the commonly accepted interpretations.
I don't see much of a point in simply agreeing with the interpretations we have as supposed to trying to find interpretations that fit all the data we have collected- that is, including dark matter and dark energy.
So... tell me, if you are so knowledgeable of the subject... tell me what you think about our galaxy. Do you think there is really dark matter in our galaxy or the anomalies we observe in the galaxy's rotation patterns can actually be explained without dark matter? What about quasars? Do you think they would behave exactly the same way our galaxy does, but with a much bigger scale? Or there is something special about quasars?
What do you think is the shape of the universe? It sounds like you believe the universe is like a sphere...
I am not in least bit offended Please Register or Log in to view the hidden image! all i want to know is what is the (hard core)
to cosmology and why people think they are on the right track.
It is unfair of scientists to propose way out theories and then talk down to us
because we are to stupid to accept them chapter and verse.
Maybe a theory can be right with 95% of it missing but, is it questionable?
to right it is.
so the universe is either infinate in size wich allows matter to expand into itself, or it has walls and limits,
There are no walls, the universe can be infinite but bounded, all this means is
that from where ever you start a journey, traveling in a straight line you will
all ways eventually end up back at your starting point,
That is not including the expantion of space, with this you will never reach
your journey's end.
you cant end up where you started at unless you just walked in a circle or around a sphear like the earth, there is nothing indicating that the universe is a sphear. how do you explain ending up where you started at?
Have a look at this wiki article.
A compact space is a general topological definition that encompasses the more applicable notion of a bounded metric space. In cosmological models, it requires either one or both of: the space has positive curvature (like a sphere), and/or it is "multiply connected", or more strictly non-simply connected.
If the 3-manifold of a spatial section of the universe is compact then, as on a sphere, straight lines pointing in certain directions, when extended far enough in the same direction will reach the starting point and the space will have a definable "volume" or "scale". If the geometry of the universe is not compact, then it is infinite in extent with infinite paths of constant direction that, generally do not return and the space has no definable volume, such as the Euclidean plane.
If the spatial geometry is spherical, the topology is compact. Otherwise, for a flat or a hyperbolic spatial geometry, the topology can be either compact or infinite.
that doesent mean that if you keep going straight that you will end up where you started, for expansion to take place from what we can gather from lab experiments and actual tests we conduct, you need existing space for mass to expand into,
an infinite universe would explain this, your theory relys on dark energy if i am not mistaken?
i will read the wikipedia page now.
I think there's some confusion here about how science actually works in practice, and what scientists do.
Fair comment. Scientists do not yet know what the missing mass is. But that's ok. There are always things we don't know about the universe. On the edges of knowledge, people are always searching for explanations, and what is happening in cosmology is the same as is happening in stem cell research, or nuclear fusion research, or any other area of cutting-edge science.
I don't know how you think new knowledge is generated. You must realise that at some stage every "fact" goes from being unknown to known and accepted. And that means that science will never have all the answers. Science is a gradual pushing back of the limits of knowledge.
As far as I am aware, brane theory is completely compatible with the big bang. I personally am not a string theorist, so I'm not qualified to comment on the ins and outs of brane theory. To do so would be worth little more than an uneducated guess.
That's correct. I am not a cosmologist. I am not an expert in general relativity, even. I've only taken one graduate-level course in GR.
I know how much I don't know.
I prefer to leave the development of cutting-edge cosmological theories to people who have chosen to dedicate their lives to the field of cosmology - the experts in that field. Who am I, who knows almost nothing in comparison, to say that my guesses about cosmology are better than their informed analyses?
Would you tell an electrician how to fix the wiring in your house? If you're qualified to do that, perhaps you'd just fix it yourself. But if you're not an expert, you leave that stuff to the experts. So why, when it comes to experts in academic fields, do people presume that their opinions are just as good as those of the people who have studied and whose job it is to work on those things?
What I would ask is: Are you qualified to challenge the interpretations? Can you understand brane theory sufficiently to comment on it? Can you do the math? And if not, what on earth makes you think you'll come up with anything remotely useful in that field, that hasn't already been carefully examined by the real experts?
I don't know what shape the universe is. The visible universe is certainly a sphere - light has only been able to travel for 14 billion years or so, so we can't possibly see anything further away than the edge of a sphere 14 billion light years in radius. But what is beyond that? There's no way of knowing.
As for the spacetime geometry of the universe on the largest scales, current data says it is approximately flat (in 4D). The accelerating expansion is thought to be due not to spacetime curvature, but due to the presence of "dark energy", which appears in Einstein's equations as the "cosmological constant".
A pushing or a pulling effect? The acceleration I mean. Do they know?
Well, we're talking about dark energy that exists between and within galaxies, so I guess it's a kind of push outwards - an anti-gravity effect.
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