Strange Posted August 19, 2019 Posted August 19, 2019 1 hour ago, dimreepr said: So lets start with a definition. Searching for the phrase "time is what clocks measure" pulls up this interesting article: https://www.pitt.edu/~jdnorton/Goodies/What_is_time/index.html 1 hour ago, Airbrush said: This is a model of a big bang that had no beginning? The scientific language and math intimidate me. It is above my level of understanding, so could you summarize it for us please? As far as I can tell, rather than saying that you can extrapolate back (linearly and naively) to get to a zero sized universe of infinite density, instead you can go further and further back presumably asymptotically approaching that state but never getting there. This may be related to an odd paradox in symmetry breaking (that I came across years ago and haven't been able to find again) where a system can be in a metastable state (imagine balancing a ball bearing on the top of a sphere) for an infinite time before it spontaneously decays to a stable state (the ball bearing rolls down). This is kinda like the "universe from nothing / quantum fluctuation" idea, but instead of being from "nothing" is is from a hot, dense, metastable state. But I may well be reading too much into it. I haven't seen a good, comprehensible description of that research. And it is very preliminary; using an approximation of quantum effects in GR.
StringJunky Posted August 19, 2019 Posted August 19, 2019 41 minutes ago, Strange said: Searching for the phrase "time is what clocks measure" pulls up this interesting article: https://www.pitt.edu/~jdnorton/Goodies/What_is_time/index.html As has been said before: one does not agonise over distance and pontificate on the ontological properties of it, nor should one do the same for any other parameter, of which time is one.
Strange Posted August 19, 2019 Posted August 19, 2019 To paraphrase Gag Halfrunt, “Time’s just this parameter, you know”
StringJunky Posted August 19, 2019 Posted August 19, 2019 (edited) Yep. It is deeply resistant to a complex explanation because it's, like, simple. Edited August 19, 2019 by StringJunky
koti Posted August 19, 2019 Posted August 19, 2019 (edited) 1 hour ago, StringJunky said: Yep. It is deeply resistant to a complex explanation because it's, like, simple. Simple - Yes and no. I think. We know its got an arrow, we know it „bends” along with space under conditions which implies its got „interactive features” which further might imply that time is a thing. But that does not have to be true... just like space is volume, time might just be analogous to volume. On the other hand, we don’t even know if time had a beginning and it might not be a valid question whether there was a beginning to the Universe because conditions at t=0 were so much different from what we see now. Most theorerical physicists agree that GR has to be eventually complemented by a fuller theory and not just because we need to marry gravity under QM and GR but more fundamentally, we don’t know what gravity and spacetime fundametally is. It is pretty obvious (at least to my lame, amateur mind) that what we define as gravity is just a „leak” of something more fundamental, maybe time and the concepts of beginning/before/after are a part of something larger too on the cosmic scales. One thing we can be sure of, our gut is a bad adviser due to our evolutionary handicap of living is our small Earth bubble. There hasnt been a revolution in my lifetime in physics, I hope the next ~30 years will erect one so I can witness it Edited August 19, 2019 by koti 2
MigL Posted August 19, 2019 Posted August 19, 2019 Space-time is geometry. We know that at sufficiently small scales ( Planck ), geometry ceases to have meaning. Until we can be sure of the 'size' of the seed from which our universe sprang, we can't be sure if space-time is a meaningful concept that can be applied ( in that primordial era ).
Airbrush Posted August 20, 2019 Posted August 20, 2019 23 hours ago, Strange said: As far as I can tell, rather than saying that you can extrapolate back (linearly and naively) to get to a zero sized universe of infinite density, instead you can go further and further back presumably asymptotically approaching that state but never getting there. This may be related to an odd paradox in symmetry breaking (that I came across years ago and haven't been able to find again) where a system can be in a metastable state (imagine balancing a ball bearing on the top of a sphere) for an infinite time before it spontaneously decays to a stable state (the ball bearing rolls down). This is kinda like the "universe from nothing / quantum fluctuation" idea, but instead of being from "nothing" is is from a hot, dense, metastable state. But I may well be reading too much into it. I haven't seen a good, comprehensible description of that research. And it is very preliminary; using an approximation of quantum effects in GR. Are you saying that the big-bang region of the universe (because we know nothing about the region beyond our visual horizon) may have existed for an infinite time in a strange state before changing at the moment the big bang began expanding?
Strange Posted August 20, 2019 Posted August 20, 2019 1 hour ago, Airbrush said: Are you saying that the big-bang region of the universe (because we know nothing about the region beyond our visual horizon) may have existed for an infinite time in a strange state before changing at the moment the big bang began expanding? That’s about it. But I don’t think it is necessarily a strange state; just hot and dense. And ready to expand.
Mordred Posted August 20, 2019 Posted August 20, 2019 There were a few theories on this. They didn't last long for whatever reason.
Strange Posted August 20, 2019 Posted August 20, 2019 Yes. Disappointed not to have seen any follow up on this.
Gater Posted September 5, 2019 Author Posted September 5, 2019 On 8/11/2019 at 11:45 AM, Mordred said: Belief isn't science. As mentioned you need to show a scientific reason not based on belief that the universe is infinite and that it has always been here. Current observational data shows that our Observable universe is finite to the limit of our observation. However we know there is more beyond that. It also shows that the Observable portion had a beginning when you extrapolate expansion back into the past. As far as the entire universe we have no way of knowing if it's finite or infinite. So what evidence can you present other than belief for an infinite universe over a finite universe? Space is the absence of matter - I say it can not end - just as Aristotle said - Logically it can not end. What do you believe and why?
Mordred Posted September 5, 2019 Posted September 5, 2019 (edited) Well space is simply volume that is correct however belief in whether a volume can end or be created is pretty much meaningless and irrelevant to the universe creation scenario. What the BB model under LCDM describes is our observable portion which amounts to our shared causality region. Reverse expansion and that shared causality region is smaller than an atom. Prior to that is speculative Edited September 5, 2019 by Mordred
Gater Posted September 5, 2019 Author Posted September 5, 2019 I think a lot of the misunderstanding comes from not being clear on what each term means. Some use the term Universe as infinite space, and some use Universe as Observable space. Most use the term "space" and think of the night sky. When I look at the night sky I see space and matter.
Mordred Posted September 5, 2019 Posted September 5, 2019 Well that is certainly true a lot of confusion arises in simply not realizing our models describes our Observable universe which in itself is finite and had a hot dense state as far back as we can model. Unfortunately space as in outer space and the physics/geometric definition of space often get confused. As far as the universe in its entirety beyond our observable universe it could be finite or infinite. We have no way of knowing and are likely to never have a means of knowing.
Gater Posted September 5, 2019 Author Posted September 5, 2019 So why wouldn't space be the same as the geometric model?
iNow Posted September 5, 2019 Posted September 5, 2019 4 minutes ago, Gater said: So why wouldn't space be the same as the geometric model? Because non-mathematical human language is imprecise 1
Mordred Posted September 5, 2019 Posted September 5, 2019 Excellent answer +1. A good example of imprecise verbal descriptives is spacetime curvature. When you study the math itself without wordplay you learn it means the freefall paths become curved. Example the worldline of a photon
Gater Posted September 5, 2019 Author Posted September 5, 2019 Im talking about endless space - how could it ever end?
Mordred Posted September 5, 2019 Posted September 5, 2019 (edited) The model descriptive for an infinite universe (more accurate in this case ) would be an open universe. With closed universe being finite. For the latter case it could be something like the surface of a ball. Ie loop back onto itself ( toriod shapes got discounted on CMB measurements). Give you an example after the 2012 Planck results and the slight positive (closed) error margin. A study if closed and on that dataset if you were to stop expansion a light would take 880 Billion years to transverse and loop back to the emitter. Though measurement of a critical dense universe (flat) ie extremely close to it we are also viable for an infinite universe. (Open) due to Lambda cosmological constant. Edited September 5, 2019 by Mordred
Strange Posted September 5, 2019 Posted September 5, 2019 6 hours ago, Gater said: Some use the term Universe as infinite space, and some use Universe as Observable space. Some use the term universe for the entire universe which may be finite or infinite as we have no way of knowing how large it is.
Gater Posted September 5, 2019 Author Posted September 5, 2019 You still haven't given an a answer as to how it could end - Aristotle called the Universe borderless - im going with him. Until the scientific community can come up with a plausible explanation of HOW it can end - im going with infinity.
Strange Posted September 5, 2019 Posted September 5, 2019 11 minutes ago, Gater said: You still haven't given an a answer as to how it could end - Aristotle called the Universe borderless - im going with him. Modern cosmology says it is borderless too. But that doesn't tell us whether it is finite or infinite. You have been given an answer as to how this could be. You either missed it, failed to understand it or just dismissed it because it didn't agree with your belief system. How about a 2D analogy? If we have a 2D surface which has no boundary then it can be infinite (for example, a flat surface that goes on for ever) or it can be finite (for example the surface of a sphere). The same is true in 3 (or more) dimensions.
Gater Posted September 5, 2019 Author Posted September 5, 2019 On 8/12/2019 at 5:53 PM, J.C.MacSwell said: +1 Perfect logic requires the right assumptions, and we can't be absolutely sure about the ones we have taken on. Right - So if the Universe has always been here - any attempt to discover a "beginning" would be logically flawed. 1 hour ago, Strange said: Modern cosmology says it is borderless too. But that doesn't tell us whether it is finite or infinite. You have been given an answer as to how this could be. You either missed it, failed to understand it or just dismissed it because it didn't agree with your belief system. How about a 2D analogy? If we have a 2D surface which has no boundary then it can be infinite (for example, a flat surface that goes on for ever) or it can be finite (for example the surface of a sphere). The same is true in 3 (or more) dimensions. If its borderless - it means its infinite.
J.C.MacSwell Posted September 5, 2019 Posted September 5, 2019 45 minutes ago, Gater said: If its borderless - it means its infinite. The surface of a sphere is borderless...yet finite.
Strange Posted September 5, 2019 Posted September 5, 2019 1 hour ago, Gater said: Right - So if the Universe has always been here - any attempt to discover a "beginning" would be logically flawed. Why is it logically flawed? You are just saying that without showing any logic. You may believe the universe has always been here but you have provided no evidence or logic to support that belief. 1 hour ago, Gater said: If its borderless - it means its infinite. Did you miss this: 1 hour ago, Gater said: How about a 2D analogy? If we have a 2D surface which has no boundary then it can be infinite (for example, a flat surface that goes on for ever) or it can be finite (for example the surface of a sphere). The same is true in 3 (or more) dimensions. The surface of a sphere is unbounded but finite. In case you missed it again: The surface of a sphere is UNBOUNDED but FINITE.
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