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Dark Matter Measurements
ksp0704 writes: "According to this article at space.com, scientists have finally measured the approximately 90% of the universe we can't see (the dark matter)." I'm sure it will continue to be a topic of debate for years, but two independent measurements agreeing is a good sign.
So apparently they think that the part of the universe we can't see is dark matter or something? And they seem to be able to guess how much of it there is. I believe that the universe has always existed, and will continue to exist forever. It is also infinitely large in every direction. The only reason we can't see the rest is because the light hasn't gotten here.
When you shine a flashlight at a wall you can see that light spreads out as you move farther away. The stars are so far away that the light does not reach the little tiny tiny earth.
Even better. Maybe the universe wasn't always here, and it had a "creation" date. We think the universe is "expanding". Maybe it's because that light from that far away takes a certain amount of time to get here. So light from farther away places is arriving here for the first time ever. if we can figure out how many light years the farthest away thing we can see is, then we can figure out how old the universe is.
I still think it's amazing that when you look at the stars in the sky that you are looking billions of years into the past. Those stars you see where there before dinosaurs were here, and they might not even be up there anymore.
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Heh. What's the difference, if it's all just theoretical anyway? I mean, really, how is the amount of matter in the universe ever going to mean anything more to us than simply a numerical value?
Of course, one can assume that, by knowing the ammounts of normal matter compared to dark matter as they change, scientist could predict approximately when the universe would collapse on itself. You know, if the big bang theory has any truth to it. Of course, that prediction wouldn't mean much to us either, as our sun will likely die out long before the universe itself will.
I'm only in high school physics, maybe someone more familiar with the field could provide an explanation and how it relates to the facts presented in this article?
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When the whole universe collapses because of the reversal of the big bang energy by gravity, then you may care.
One of the biggest debates IMHO, is whether the gravitational pull of the universe can overcome the expanding motion of the universe. This expansion caused by the big bang was theorized to be decreasing and gravity would eventually overcome it, thus pulling the entire universe back together in the same manner of pre-big bang time. It could also be said that this would cause the universe to be a periodic function of explode, expand, contract, explode... The problem with this is that there is not anywhere near enough matter in the universe to create a gravitational pull strong enough to overcome the big bang energy. There is also not enough visible matter to explain many gravitational effects scientists perceive. Thus, dark matter was theorized to explain these phenomenons. However, it could never be measured. This could go a long way to supporting various theories about the universe and it's workings.
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Everything has a reason, even if it is a loophole. God either does or does not exist, but there is a reason for it. The big bang theory either is or is not true, but there is a reason for it.
Here's the loophole in your argument.
According to Godel's incompleteness theorem, in every nontrivial logical system there exist statements which are either simultaneously true and false (such systems are generally frowned on) or are impossible to prove either true or false.
Mathematics is one of the later. Thus there are statements in mathematics which can be written down but never proved true or false (no easily explained examples exist). It's possible that such a property can be correct, in that it does hold in all possible cases without being able to prove that it does, and of course we can't actually test all cases to know that way.
By extention it doesn't follow that there is neccesarily a reason for the big bang being true or not true. There doesn't strictly have to be any explanation for why it is the way it is.
Of course this is a somewhat silly argument because there probably is a good deal that can be explained about the big bang, and much of science rests on inference and not proof (in the mathematical sense), but it is interesting that even in mathematics there are things for which there can be no reason (ie. proof).
What caused the big bang? How was it initiated? What were the bounds of the "universe" as it were before the big bang?
Sometimes bored physicists do try to give serious thought to this. Being a physicist, I've sometimes gotten to listen to what others consider to be serious thoughts on the matter.
Basically there are too camps, people that want the universe to be timeless and exist forever and people that want the Big Bang to be the ultimate start of things. People in the first group will given you various stories about the cyclical nature of the universe (usually expand, collapse, repeat), or some notion of universes spawning other universes, ad infinitum.
People who believe that the Big Bang was THE START of things tend to either believe it to be uncaused, caused by God, or unknowable and irrelevant. There are a few however in this camp that try to posit explanations of what did cause the universe out of nothing. Some bring in exotic theories (such as string theory) to try and construct physical laws that can hold before, during, and after a big bang event. Of course these people also have to change the nature of a big bang away from that strictly based on general relativity (which implicitly prevents any meaningful reference to a "before" the big bang).
One of the most interesting stories I've heard is that the fabric of space has the property of being unstable in a total absence of energy, and at any moment and any location, there is infinitesimal but non zero probablity that it will transition to a different state which has energy, which then billows out into the rest of the universe. So basically the vaccuum has certain properties that exist forever and are timeless, and the big bang has a chance of spontaneously erupting simply because it has never happened. Hence the universe, as we expereince it, has a single well defined start within a larger timeless existence.
As absurd as this might sound, this is quite serious, and as reasonable as many other things people say about "before" the big bang.
Ultimately though, it only transfers the problem of first cause to the "fabric of the universe" and the basic physical laws governing everything. While science may be able to tell you that something is NOT the first cause, it can never say with certainty that something IS the first cause. As far as I'm concerned, whether you choose to believe that the chain of causation goes infinitely backward or has some definably beggining, is a matter of faith.
If bright matter truly makes 10% of the universe, then by definition the remaining 90% of the universe must be dark matter.
The reason is that neither the terms "bright matter" nor "dark matter" specify a single type of matter. Rather, they define two values of a single common characteristic of all matter. The characteristic in question is how the matter interacts with photons. If you shine a light on something and you can see it, then it's bright matter. If you heat something up and you can see it, then it's bright matter. If you energize something then let its energy level drop and you can see it, then it's bright matter. Otherwise it's dark matter.
Therefore we can't measure dark matter directly merely because we can't see it. All astronomical observations depend on photons. Radio. Light. X-Ray. Gamma. Just different frequencies of photons. Since dark matter neither reflects nor emits photons, astrophysicists can't observe it. Or perhaps it does emit photons, but then immediately reabsorbs them (as in the case of black holes). Either mechanism comes down to the same thing. They can observe its effects indirectly by watching, for instance, the effect that its gravity has on surrounding bright matter, but no direct observation is even theoretically possible.
But there really aren't any theories about the nature of dark matter, because it's fundamentally impossible to observe remotely. Maybe it's some truly strange substance. Maybe its just a whole bunch of black holes. No one knows. The only reason that we know about black holes is that some brilliant physicist who'd been downing a few too many beers one night did a thought experiment about the implications of gravity's inverse square strength. So we had a theoretical phenomenon that astrophysicists could later go and look for. But that's not true of other forms of dark matter.
All that's important is that "dark" matter is every piece of matter that isn't "bright" matter. It's still matter, and will still behave exactly the same as bright matter behaves. But it may come to be discovered that some characteristic that we thought was endemic to all matter is, in fact, only endemic to bright matter. We have no comparison yet, so we can't make that determination.
I don't think that anyone believes that all dark matter is in the form of black holes. Who knows, maybe so. I'm certainly not an astrophysicist (though I know a number of them who are on the bleeding edge), so someone can easily have come up with some theories about all this of which I'm unaware.
But this is my current understanding, and with the rate that astrophysics moves, I'm probably at least 5 years out of date.
Oh, explaining this caused me to remember a theory about dark matter that I heard from my undergraduate adviser back in my college days (Dr. Douglas Lin: he was and is a big shot in the astrophysics circles). The idea is that there actually isn't any special dark matter. It's all bright matter. But some matter might be in locations where so few photons fall on them that we just never get a chance to observe that matter. For instance, it's known that all the galaxies of the universe exist on the surfaces of voids in the universe (that observation is what gave rise to superstring theory). Think of soap suds. We've got complex surfaces, where all the soap is, each surrounding a small void with no soap. Small from our perspective, but from the point of view of a technological civilization living in one of the "galaxies" within the soap film, those voids are huge. The universe has the same structure. And these voids are just monstrously huge. In the center of one of these voids, there would be very little light, because all the light sources are very far away. So you could stick a whole lot of matter there and no one would ever see it. These voids are so huge that you could easily fit 90% of the universe's mass in them and still have a very low density of matter. It's normal "bright" matter, but insufficient light reaches it for us to observe it. The problem with the theory is that if you have 90% of the universe stuck in these voids, then the voids should collapse from gravity and make the galaxy distribution homogenous. And we don't see that. Perhaps this problem has been resolved by now. I don't know. And, of course, there are other locations where matter can be hidden, where we wouldn't be able to observe it. Those voids are just a single example.
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A further problem not mentioned in the above is that the angular motion of spiral arms is such that the speed of star motion is much more consistent from the center of the spriral to the outside of the spiral then they should be. It is almost as if they were a solidf or semi-solid disc. which is silly, but that is how they behave.
This may be less consistent with a high energy point source of gravity, and more consistent with mass spread out for a large distance. but I haven't kept up and my math sucks [smile]
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there is no way (at least with current limitations) to accurately predict a model with that many variables (for example, weather).
:-(
That's not true. Just because there are trillions of factors happening every nanosecond does NOT means that it is not predictable, it just means that we may not have the means to predict it. This however does NOT make it random. Is there any way for you, as a human without tools, to look inside a CPU and predict exactly what electron will be where and a what point in time? No, of course not, however the processor is working in a very predictable nature.
there is also free will, or choice
That is my paradox. According to the fundamental rule that I have laid out (there is no spoon, er shit I mean there is no randomness) that also means that there is no free will. Sorry, one cannot coexist with the other. Free will explicitly denies predictability, and thus implies randomness.
I will not, no, I cannot accept this. Thus there must be randomness in the universe. The only plausable explination that I can find is that there are forces acting outside of the universe / this dimension that have effects on the inside of this universe. With this there is still no randomness and there is still free will, however now I've implied that there is something supernatural about our existance (like perhaps our "souls" exist in a different dimension?), and that is a whole new ball of wax to get into.
So I'm still in a quandary
If God gave us curiosity