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  2. Pressure, as commonly understood, is not easily related to General Relativity. However, if we think of space-time as a coiled spring, it is easy to understand that if you compress that spring, you increase its energy, and the curvature of space-time around it. An easy to understand excerpt from https://ned.ipac.caltech.edu/level5/Guth/Guth3.html explains the relationship between pressure, energy density, space-time curvature ( gravity ) and expansion/inflation. "THE PRESSURE OF THE FALSE VACUUM can be determined by a simple energy-conservation argument. Imagine a chamber filled with false vacuum, as shown in the diagram below. For simplicity, assume that the chamber is small enough so that gravitational effects can be ignored. Since the energy density of the false vacuum is fixed at some value uf, the energy inside the chamber is U=ufV, where V is the volume. Now suppose the piston is quickly pulled outward, increasing the volume by dV. If any familiar substance were inside the chamber, the energy density would decrease. The false vacuum, however, cannot rapidly lower its energy density, so the energy density remains constant and the total energy increases. Since energy is conserved, the extra energy must be supplied by the agent that pulled on the piston. A force is required, therefore, to pull the piston outward, implying that the false vacuum creates a suction, or negative pressure p. Since the change in energy is dU = ufdV, which must equal the work done, dW = -pdV, the pressure of the false vacuum is given by p = -uf. The pressure is negative, and extremely large. General relativity predicts that the gravitational field which slows the expansion of the universe is proportional to uf + 3p, so the negative pressure of the false vacuum overcomes the positive energy density to produce a net repulsive gravitational field. "
  3. All forms of redshift are additive. It is plausible to counter cosmological redshift by gravitational or Dobbler shifts. They may have different causes however the effects upon frequency is the same. It's simply a matter of finding the right combination.
  4. I enjoy MOM from US, and 'Somewhere street' on NHK.
  5. Today
  6. Because you can’t actually be in equilibrium during the process and have it take a finite time
  7. The worst thing about "free to air TV" in Australia, is the flooding with these idiotic so called "reality" TV shows. They literally make me want to be sick!!
  8. it doesn't sound right because ratio of distance traveled by the body to distance traveled by light is 6/28000. and the redshift definitely won't happen at the destination. it happens through time. so it already happened when they meet (little less than intended but look at the ratio, the damage is done) but it should be like what you said. because if we consider hubble constant (or if we need to, the accelerating rate) the spacetime is expanding with that rate and considering the direction of light toward body and direction of body toward earth and light ray, then expanded distance and time would be accounted for. can some one help me with this?
  9. Sorry, I've been a rather busy little beaver. Others have explained the BH, EH and GR correctly. Secondly all matter/energy warps or affects the geometry of flat spacetime, [it curves, warps, twists spacetime] and we feel that geometry as gravity. So any perfect vacuum, that is space without any light or any form of energy would be perfectly flat. The only possible perfect vacuum state I think [willing to be corrected on this] is inside the EH of a dormant BH, that has obtained perfect temperature equilibrium with the outside. And while this is certainly curved by the collapsed mass at the core, it does not "no gravitational influence of its own" to pinch the phrase from Phi for All.
  10. Can you explain what you mean? For example suppose I take [0,1] and reorder it in the reverse standard order. So that a <* b iff b < a. Then the reordered set looks like this: 1-----3/4----1/2----1/4----0 I don't see how you get a square from this. > Edit: I might say (S,<*) is S with a and b removed and = {x: a<*x<*b}. What exactly is S? What are a and b? It would help if you clearly define your notation. If S is some set, then S = S throughout your discussion. And if S is an ordered set with standard order <, then (S, <*) must be the EXACT SAME SET with a different order. You can't change the meaning of S in mid-argument. You could say that T is S with a and b removed, but you can't say that S loses elements by virtue of reordering. That's bad notation and confusing exposition. What is a reordering of a set? A reordering is just a bijection from the set to itself. The set is exactly the same before and after. A reordering is just a choice of some bijection from the set to itself. The elements remain the same.
  11. Of course one must consider that distances will vary with solar sails due to having to tack. Just like a sail boat if you are approaching the sun then the route will be longer There is advantages in a propellant craft in this regard. Though it is quite advantageous to have a combination to save on fuel payload where viable
  12. Why there is no reversible process in the nature? At any level? What about quantum level? So, if reversible processes would exist in the nature and practically achievable in a reasonable time intervals, then we would be able to create a perpetuum mobile which is capable to produce some sizable useful work? Or...not?
  13. Another solar-powered, propellentless craft described here: https://www.universetoday.com/142894/lightsail-2-is-sending-home-new-pictures-of-earth/
  14. Why are you asking? Or, more specifically, why are you asking me?
  15. ! Moderator Note As the OP has been given a a few days holiday from the site, this thread is closed. (Also because it is nonsense.)
  16. The water would rush to fill the empty space. This would be an extreme form of cavitation: https://en.wikipedia.org/wiki/Cavitation There is no negative state, in terms of mass or energy (or the presence of matter). No. A (perfect) vacuum is zero mass (and energy). There is nothing less than that.
  17. There is no connection between them. The uncertainty principle is about a limit to which things can be measured, even without any effect from the observer.
  18. ! Moderator Note If you have a new idea, please feel free to start a new thread in Speculations. If you want to ask questions to clarify your understanding, please start anew thread for your questions. Thank you.
  19. I was mostly thinking for kids . Its annoying sometimes when porn is all over the place when you don't want it . There is too much porn related ads in the mobile devices too these days . Only YouTube kids is sort of free from it . I am from India , It has banned at least 800 porn sites here even though it is a democratic country . I thought it would be a nice rule to be implemented No too serious about it like the beginning of thread says
  20. It seems odd that the biggest search engine throws everything at you by default and compromises your privacy and StartPage and DDG protect your privacy and make exposure to nudity porn an opt-in feature.
  21. I have a new theory about this, but I don't know if things work as I expected. So I need to make sure certain things before I feel comfortable to talk about what I came up with.
  22. I would change "no gravity" in this instance to "no gravitational influence of its own". If you had such a vacuum, and suddenly introduced matter into it, it would still be affected by spacetime curvature from any nearby massive objects. I'm being nit-picky, but "not generating any gravity in the area of a vacuum" is different from "gravity doesn't affect the area inside a vacuum", so I wanted to make sure of what you meant by "no gravity".
  23. Are there any scientists tried to relate the two, in hypothesis and calculations?
  24. The right wing has wanted a war with Iran for decades. With today's news of a British tanker "accidentally" veering into Iranian waters, it seems everything is being done to stoke a conflict at this point. https://www.theguardian.com/world/2019/jul/19/british-tanker-iran-capture-fears-stena-impero-uk-ship-latest Everything that's happening now seems like a provocation.
  25. Thanks guys. It's very clearly explained. Thanks Strange and Mordred.
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