# Tag Info

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Thank you all responses. We know that these approaches are carried the string theory (as well as mathematical and physical). In fact I have to ask my question as follows: How can we model mathematically parallel universes without any restriction (for example topology on the universe)? I mean, is it can be modelled using only set-theoretic. If there exists ...

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We all know that energy is never lost, but it transforms into another form.  Actually, in General Relativity it is possible for energy to change. But energy is also frame dependent (in any theory) and there is no obvious frame in General Relativity in general. Doesn't that mean that energy is not unlimited? No, even if you used Special Relativity ...

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It is indeed possible to both have a infinite universe with finite total energy. Pose that there is only a part of the universe that is occupied with energy. This region will grow at the speed of light but will still be finite. The other way around (finite universe-infinite energy) is the only combination i find impossible because it implies an infinite ...

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There are probably duplicates/variants of this question on this site. Expressing the problem in mass terms seems a bit odd to me though, as it's been put in energy terms every other time I have seen it asked, unless I have misunderstood your question. Here is an answer (to an identically worded question) based on the link: Predicted Mass of Quantum Vacuum ...

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Photons (radio waves, "light", gamma-rays, etc.) and neutrinos contribute negligibly to the total energy density of the Universe. By far, most of the photons that exists today are the cosmic microwave background, with 450 photons per cm$^{3}$ (e.g. Hobson et al. 2006). The number density of neutrinos is similar, 330 per cm$^{3}$. In total, the energy density ...

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Okay, let's start with the basics. The Big Bang was not like an explosion in space from which spewed all matter in the universe. The Big Bang was a moment in time. We have this thing called a spacetime metric. I won't bore you with the details, but essentially it is the equation we use to describe all of the geometry in the universe. It includes all the ...

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If you're asking whether there is any chance we'll be able to do this in the forseeable future then answer is no. If, however, you're asking whether general relativity allows constructions like this then the answer is yes. Your question refers to a brane which would exist inside a bulk of our own design, and I don't know how literally you meant this but it ...

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The "catches" as you call them are at least threefold: Cellphones require transmission and receiving hardware that fit in your hand / desktop computer and be almost omnidirectional, i.e. able to receive transmissions from any direction. In contrast, deep space probes are tracked with extremely directional, huge antennas of hundreds of meters diameter ...

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I) If there are boundaries, how can we know about what happens there with entropy? The preferred way to think of the universe today is that it does not have any boundaries. But there is no way to be sure unless we find such a boundary. If our universe was enclosed inside a perfectly rigid hull impenetrable to everything including gravity (infinite ...

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Firstly, string theory is a mathematical hypothesis that is currently speculative. It is a possible candidate for a quantum theory of gravity - a unification of QM with Einstein's theory of gravity - General Relativity. The idea of superstring theory emerged from another theory called supergravity. Supergravity was an attempt at a supersymmetric theory of ...

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The hubble relation is: $$v = H d$$ where $v$ is the velocity of the galaxy relative to the Milky way, and $d$ is the distance of the galaxy relative to the milky way. The velocity is measured using redshift. The distance is measured through a complicated series of standard candles, along with the relationship $I = \frac{I_{0}}{4\pi r^{2}}$. If you ...

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The number of atoms in the universe is not known to be infinte or finite. The biggest problem is that we cannot see all of the universe. The universe is only 13.8 billion years old, meaning that we can only see 13.8 billion light years in any given direction. This portion of the universe, usually called the "observable universe", has been estimated to ...

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However, if that is the case, than everything would technically pull on everything, right? No. A gravitational field is a place where space is "neither homogeneous nor isotropic". You can See Einstein talking about that here. And the FLRW metric "starts with the assumption of homogeneity and isotropy of space". I'm confident that this is correct ...

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I describe how to calculate the Hubble parameter in How does the Hubble parameter change with the age of the universe?. You should have a quick read through this as it's relevant to the rest of your question. We know the universe is expanding. We describe its size by a parameter called the scale factor, $a$. The rate of expansion is the rate of change of ...

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I am attempting answering my question based on one fact and one assumption (actually there are one more fact/ observation - Redshift): The fact is: inertial frame. which, to a good approximation, earth itself (ignore its rotation, irrelevant to our discussion) is an inertial frame. The assumption is: Earth is no special place. Hence the logical ...

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Lie down and fall asleep. Right on the razor's edge between awake and asleep, look at what it all looks like. See yourself and the world in unison, fading away... slowly, and at the same time instantaniously. Then, in the morning, be thankful that your experience was merely that of falling asleep, and not a more permanent heat-death. (The question is ...

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General Relativity is about describing (the dynamics of) a curved spacetime. So you need a collection of events, and a metric that tells you the interval between nearby events. That's it. You can a stress energy source term too. But anything else is either unphysical or a straight up bias brought into a theory for no reason. There are some easily ...

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I think you have a fundamental misunderstanding of what the heat death really is. Any observer, whether they are a time traveler, observer from another universe, or whatever, would just see a lot of empty space. The first thing to know is that the heat death is not a single event. The universe, after heat death, is dead in the sense that nothing is ...

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Some people have very long explanations of why the universe can be created out of nothing "because the universe always does this". As a counter argument: There is no proof that the universe always does this. It is only theoretical. If you believe that the whole universe can be created out of nothing, it means you could create energy and matter out of ...

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I would say it looks like nothing. The heat death requires that the whole universe is thermodynamically homogeneous, and that the universe has reached its maximum entropy. This means that every thing becomes a disordered lump of very sparse matter, without anything to see whatsoever. It's as if the universe is in a state akin to the "chaotic nothingness" ...

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From a thermodynamical point of view, living beings are able to reduce their entropy by exporting entropy to the external world. This does not contradict the 2nd principle, since living beings are open systems. For this reason, in a thermodynamically homogeneous universe (heat death), no change in the entropy can occur, and consequently no living beings (nor ...

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These types of theories that physicists such as Krauss espouse of a "Universe Coming From Nothing" are quite flawed, as by no means are they talking about nothing! Further, the concepts of particles, mass, and energy are not even well-defined when talking about the universe in general. I wrote a paper on this (excuse the shameless self-promotion), it can be ...

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Can space be destroyed? I can only give an opinion here, not some authoritative answer. But my opinion is based on Big-Bang cosmology and general relativity, so hopefully it isn't total junk. We have evidence that the universe is expanding, and this evidence looks pretty good. When we project backwards by 13.8 billion years, we surmise that all the ...

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Some galaxies are known to be expanding away from us faster than the speed of light. This is only possible if it is the underlying universe getting bigger. It isn't possible that these galaxies are simply moving faster than the speed of light as your argument suggests as this violates the principles of special relativity.

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