Mordred Posted October 16, 2017 Posted October 16, 2017 29 minutes ago, koti said: One could think that Mordred is cocky if one did not know Mordred Ego is best left at the door on Mordred's couch . Lol no place for it in science.
Cosmo_Ken Posted October 16, 2017 Posted October 16, 2017 Thank you Mordred and Strange, you have given me a number of links to check out! I have two other questions. First, so a recent NASA press release that said that they had observed the most distant galaxy yet, at a distance of 13.8 billion light-years, was wrong? Secondly, is the red-shift we observe with most galaxies strictly the result of the relative motion of the galaxies relative to space, or does it include the effect of the expansion of space too? Cheers. On 10/15/2017 at 10:12 AM, Mordred said: Well in less than a second during inflation it expanded 60 e folds. Since then its expansion rate per Mpc has been slowing down. However due to quantity of Mpc. The rate of expansion of the overall volume is accelerating. What is "60 e folds"?
Strange Posted October 16, 2017 Posted October 16, 2017 45 minutes ago, Cosmo_Ken said: First, so a recent NASA press release that said that they had observed the most distant galaxy yet, at a distance of 13.8 billion light-years, was wrong? I doubt it was wrong (a link would be nice). Not sure why you think it would be.... The oldest galaxy I can find a reference to is about 13.4 billion years old: https://www.spacetelescope.org/news/heic1604/ 48 minutes ago, Cosmo_Ken said: Secondly, is the red-shift we observe with most galaxies strictly the result of the relative motion of the galaxies relative to space, or does it include the effect of the expansion of space too? For local galaxies it is entirely the result of relative motion (Doppler shift). For example, Andromeda is moving towards us. This is known as "proper motion". For distant galaxies the cosmological redshift (due to expansion) dominates.
Mordred Posted October 17, 2017 Posted October 17, 2017 (edited) Hrrm how to explain e-folding. It is in essence a doubling of volume with a time derivitave. The constant e is a derived constant. See here https://en.m.wikipedia.org/wiki/E_(mathematical_constant) in essence the universe increased in volume roughly [latex]10^{26}[/latex] to save you the calculations. Assuming 60 e-folds. More accurately distances increased by a factor 10^26. Edited October 17, 2017 by Mordred
billasker Posted February 12, 2018 Posted February 12, 2018 What does infinite even mean?The universe is of course a very big place and we cannot understand it's scale as humans.What difference does it make if it is finite or infinite?We probably won't even leave our own galaxy in the end.
zapatos Posted February 12, 2018 Posted February 12, 2018 39 minutes ago, billasker said: What does infinite even mean? "limitless or endless in space, extent, or size;" Quote What difference does it make if it is finite or infinite? To whom? To you I guess it doesn't matter at all.
billasker Posted February 12, 2018 Posted February 12, 2018 (edited) 13 minutes ago, zapatos said: "limitless or endless in space, extent, or size;" To whom? To you I guess it doesn't matter at all. Indeed it doesn't.What matters to me are things that have a direct contact with the current capabilities of human understandings.Maybe I'm wrong to think of that but what does so big you can't understand and infinite differ to you?And isn't infinity so big you can't understand it anyway? Edited February 12, 2018 by billasker
Strange Posted February 12, 2018 Posted February 12, 2018 1 hour ago, billasker said: What difference does it make if it is finite or infinite? Absolutely no difference at all.
zapatos Posted February 13, 2018 Posted February 13, 2018 6 hours ago, billasker said: And isn't infinity so big you can't understand it anyway? Not at all. Infinity isn't all that complex of a concept.
Airbrush Posted February 13, 2018 Posted February 13, 2018 (edited) My question is do you think the Big Bang is the universe? My opinion is that the universe is probably infinite in size because universe means everything, and the Big Bang may not be everything. "The Universe is all of space and time (spacetime) and its contents,[12] which includes planets, moons, stars, galaxies, the contents of intergalactic space and all matter and energy." https://en.wikipedia.org/wiki/Universe Edited February 13, 2018 by Airbrush
Strange Posted February 13, 2018 Posted February 13, 2018 4 minutes ago, Airbrush said: My opinion is that the universe is probably infinite in size because universe means everything, and the Big Bang may not be everything. The universe could be everything and still finite in size. (You can't deduce the nature of the physical world from etymology!) And the Big Bang may be only a local event in a larger universe. There may be multiple periods of expansion from hot dense state in different times and place. I doubt we can ever know. But hence the multiverse concept (a new word, because "universe" may not mean everything!)
Itoero Posted February 13, 2018 Posted February 13, 2018 True infinity is like true randomness, it can never be 'proven'. Infinity does not refer to size but to the absence of boundaries.
Strange Posted February 13, 2018 Posted February 13, 2018 2 minutes ago, Itoero said: True infinity is like true randomness, it can never be 'proven'. I'm not sure about that. Mathematical infinity can be proven. Quote Infinity does not refer to size but to the absence of boundaries. And I'm even less sure of that. Basically, it is wrong. In current cosmological understanding, the universe could be finite or infinite, but either way it has no boundary. So "infinite" is only about size.
Itoero Posted February 13, 2018 Posted February 13, 2018 1 minute ago, Strange said: I'm not sure about that. Mathematical infinity can be proven. OK, but it remains mathematical. 8 minutes ago, Strange said: And I'm even less sure of that. Basically, it is wrong. In current cosmological understanding, the universe could be finite or infinite, but either way it has no boundary. So "infinite" is only about size. Why is there no boundary?
Strange Posted February 13, 2018 Posted February 13, 2018 45 minutes ago, Itoero said: Why is there no boundary? Interesting question. I don’t know why. Perhaps because it raises the question of what is beyond it. Or because it defines unnecessary boundary conditions on the equations. 1
Airbrush Posted February 13, 2018 Posted February 13, 2018 (edited) 6 hours ago, Strange said: The universe could be everything and still finite in size. (You can't deduce the nature of the physical world from etymology!) "Everything" includes space. What about space beyond the finite-sized "everything"? We can't forget about that region. How can space not be infinite? Edited February 13, 2018 by Airbrush
Strange Posted February 13, 2018 Posted February 13, 2018 27 minutes ago, Airbrush said: What about space beyond the finite-sized "everything"? There wouldn't be anything beyond. If space is finite, it is also unbounded (has no boundary). A 2D analogy would be the surface of a sphere: this has a finite area but no edge (and so nothing beyond it). If you start walking, you will eventually end up back where you started. The same could be true of space, but in 3 dimensions.
Airbrush Posted February 15, 2018 Posted February 15, 2018 Would such a sphere have a finite diameter? If it did then you can calculate a finite distance you would need to travel in a straight line before you return to your starting point. Then you would also be able to calculate the path you could take to not end up where you started from but rather tangent off the sphere at the necessary angle to leave the surface of the curved, finite everything.
Strange Posted February 15, 2018 Posted February 15, 2018 14 minutes ago, Airbrush said: Would such a sphere have a finite diameter? Yes, if the surface area is finite. However, this analogy only considers the surface; that is the only thing relevant to the analogy. Once you start thinking about the diameter or tangents, it means that you are no longer discussing the analogy. A bit like someone describing the "rubber sheet" analogy for GR and then being asked what colour the sheet is. Quote If it did then you can calculate a finite distance you would need to travel in a straight line before you return to your starting point. You can do that even if you only consider the surface. You can measure the (local) curvature and then assume that is the same everywhere. This is analogous to the fact that curvature in GR is intrinsic curvature; it does not require spacetime to be in a higher dimensional space. (Another reason you shouldn't;t think about the inside or the outside of the sphere in the analogy.)
StringJunky Posted February 15, 2018 Posted February 15, 2018 On 13/02/2018 at 6:15 PM, Strange said: Interesting question. I don’t know why. Perhaps because it raises the question of what is beyond it. Or because it defines unnecessary boundary conditions on the equations. The problem only arises when you think ofthe expansion as an explosion from an origin.
AbstractDreamer Posted March 1, 2018 Posted March 1, 2018 (edited) If, a long time ago, a quantum entangled pair of photons were separated such that, presently, one photon is outside the observable universe for an observer and another is measured in a specific orientation by that observer, does that mean information can travel beyond the observable universe? Can the reverse be true? If locality is violated, surely then it’s possible that the interactable universe is far larger than the observable universe? Edited March 1, 2018 by AbstractDreamer Typo
Strange Posted March 1, 2018 Posted March 1, 2018 4 hours ago, AbstractDreamer said: does that mean information can travel beyond the observable universe? There is no information transferred between entangled particles. (This has been discussed many times on the forum)
AbstractDreamer Posted March 1, 2018 Posted March 1, 2018 6 hours ago, Strange said: There is no information transferred between entangled particles. (This has been discussed many times on the forum) That is a conclusion, based off a theorem, underpinned by a number of assumptions, one being that no non-local influences are at play. But you didn't address the main point, which is about the difference between the size of the observable universe, and one that it is in a coherent state.
Silvestru Posted March 1, 2018 Posted March 1, 2018 On 2/14/2018 at 12:07 AM, Strange said: There wouldn't be anything beyond. If space is finite, it is also unbounded (has no boundary). A 2D analogy would be the surface of a sphere: this has a finite area but no edge (and so nothing beyond it). If you start walking, you will eventually end up back where you started. The same could be true of space, but in 3 dimensions. So kind of like the pac-man map where you end up on the other side if you pass the edge? If you would make it spherical. Interesting.
Strange Posted March 1, 2018 Posted March 1, 2018 48 minutes ago, AbstractDreamer said: That is a conclusion, based off a theorem, underpinned by a number of assumptions, one being that no non-local influences are at play. Well, I'm not going to get into a discussion about whether quantum theory is correct or not. Quote But you didn't address the main point, which is about the difference between the size of the observable universe, and one that it is in a coherent state. As far as I know, there is no limit on the distance over which entanglement can exist; even beyond the observable universe. But I haven't ever seen anything about that. 42 minutes ago, Silvestru said: So kind of like the pac-man map where you end up on the other side if you pass the edge? If you would make it spherical. Interesting. Exactly. But trying to visualise how that woks in 3D is a bit tricky.
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