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Science and Astronomy Questions
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| Watsisname | Date: Saturday, 13.08.2016, 15:21 | Message # 691 |
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| Quote steeljaw354 (  ) Think about this for a second, think about what we could be inside of
A neat coincidence that two very different processes happen to produce similar structure. One's all gravity, the other is efficient use of space for making connections.
Quote midtskogen ( ) Or we could just say that dark matter exists, but we can't say what it is, whether it's made up of particles, is some obscure force or something else, as long as we have laws accounting for all the observations we make.
Physics doesn't speculate on what something really is, for this is unknowable, but rather seeks to understand its relationships, how it interacts with other things, so that we can produce models that predict their behavior.
Dark matter as particles is a different model than dark matter as a force. These make different predictions. We can distinguish between these, as like how we can distinguish gravitational from electric field, yet never understand what a field really is. 
Quote Huesudo ( ) My money is on lots of black holes, neutron stars, white dwarves, quadrillions of brown dwarves, and a ludicrous ammount of neutrinos.
There aren't enough of them. And neutrinos don't cluster together to form structures.
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| steeljaw354 | Date: Saturday, 13.08.2016, 15:23 | Message # 692 |
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| How big is the universe itself? Where is the proof that a big bang happened?
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| Watsisname | Date: Saturday, 13.08.2016, 15:29 | Message # 693 |
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| Quote steeljaw354 ( ) How big is the universe itself?
The visible universe (region that we can see because there has been time for light to reach us) is ~13.7 billion light years in radius (measured by light-travel time), or ~46 billion light years (by co-moving distance, which accounts for the expansion).
The size of the full universe is unknown, but at least much larger than what is observable. It could be infinite.
Quote steeljaw354 ( ) Where is the proof that a big bang happened?
Cosmic microwave background, behavior of model universes within general relativity compared with observations of real universe's evolution.
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| steeljaw354 | Date: Saturday, 13.08.2016, 15:32 | Message # 694 |
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| What does a model have to do with the actual universe? There could be forces,energies and stuff we left out waiting to be discovered. Parallel universes possible?
Edited by steeljaw354 - Saturday, 13.08.2016, 15:46 |
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| Watsisname | Date: Saturday, 13.08.2016, 15:47 | Message # 695 |
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| Models are the bridge between theory and observations.
General relativity predicts how a universe will evolve depending on what it is made of (density of matter, radiation, cosmological constant). You can use it to model the expansion history, and figure out what happens at various times. It predicts our universe began with a Big Bang, and tells us there are certain things we can look for that would support this, like the CMB.
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| steeljaw354 | Date: Saturday, 13.08.2016, 15:50 | Message # 696 |
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| How could all the stuff fit in a point smaller than an atom? What caused it to be like that?
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| midtskogen | Date: Saturday, 13.08.2016, 15:56 | Message # 697 |
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| Quote Watsisname ( ) Dark matter as particles is a different model than dark matter as a force. These make different predictions. We can distinguish between these, as like how we can distinguish gravitational from electric field, yet never understand what a field really is.
By "an obscure force" I don't necessarily mean a force that we already know about, but something we just temporarily name a force and define it mathematically to match observations. The cause of this force would be for the future to explain.
We now have some insight to share with Newton on "causam gravitatis". We don't have to view gravity as a mysterious force as Newton did, but as a consequence of the curvature of spacetime due to how matter is distributed. Matter, whatever with mass, curves spacetime. But could the curvature of spacetime also have other causes than matter?
NIL DIFFICILE VOLENTI
Edited by midtskogen - Saturday, 13.08.2016, 15:57 |
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| Watsisname | Date: Saturday, 13.08.2016, 15:58 | Message # 698 |
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| Quote steeljaw354 ( ) How could all the stuff fit in a point smaller than an atom?
The density was very high everywhere, not just at a point. This is why it didn't collapse to form a black hole (black holes require a region of high mass density surrounded by lower density).
Quote steeljaw354 ( ) What caused it to be like that?
Don't know. We have no knowledge of physics before the Big Bang, or even of the initial instant of the Big Bang itself. We can describe what happens after, from a tiny fraction of a second to today, and the distant future. We can describe how this initially very hot and dense universe evolved to become what we see today.
Added:
Quote midtskogen ( ) But could the curvature of spacetime also have other causes than matter?
And radiation and cosmological constant, but even beyond them... absolutely it could. We just have no idea what or how. We would need some kind of observations to guide us that way, and so far we have none.
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| steeljaw354 | Date: Saturday, 13.08.2016, 16:05 | Message # 699 |
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| What would you think these forums would be like in the parallel universe, what could you see the world as? There has to be a universe amongst the multiverse out there where evil=good, and good=evil. That would be interesting, wouldn't it?
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| Watsisname | Date: Saturday, 13.08.2016, 16:16 | Message # 700 |
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| I would have no idea how to speculate on that.  In a parallel universe, we might imagine almost anything.
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| steeljaw354 | Date: Saturday, 13.08.2016, 16:18 | Message # 701 |
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| What do you think the users on this forum would be like in the parallel universe? Like complete opposite
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| midtskogen | Date: Saturday, 13.08.2016, 16:21 | Message # 702 |
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| Quote Watsisname ( ) And radiation and cosmological constant, but even beyond them... absolutely it could. We just have no idea what or how. We would need some kind of observations to guide us that way, and so far we have none.
The observations that lead to the concept of "dark matter". That is, could "matter" in "dark matter" be misleading in the sense that the only thing it shares with ordinary matter is that it influences the geometry of the universe and other not yet discovered properties set it much apart from ordinary matter, including that we can't detect it in the ways we think?
NIL DIFFICILE VOLENTI
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| steeljaw354 | Date: Saturday, 13.08.2016, 16:25 | Message # 703 |
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| Could dark matter stars and planets exist? Could antimatter stars and planets exist?
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| midtskogen | Date: Saturday, 13.08.2016, 17:19 | Message # 704 |
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| Quote steeljaw354 ( ) Could dark matter stars and planets exist? Could antimatter stars and planets exist?
Watsisname can give a better answer, but I think the answers are no and theoretically respectively.
Since dark matter doesn't absorb or emit radiation, it can't collapse sufficiently to form stars etc. Stars radiate a lot.
Antimatter behaves like ordinary matter, so stars and planets could form from it, but contact with ordinary matter will cause enormous bursts of radiation. Since that is rare, the universe must efficiently have separated matter from antimatter if large quantities of antimatter exist.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Saturday, 13.08.2016, 17:20 |
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| steeljaw354 | Date: Saturday, 13.08.2016, 17:40 | Message # 705 |
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| So what would and antimatter planet look like?
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