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Showing content with the highest reputation on 07/19/19 in all areas

  1. 2 points
    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. "
  2. 1 point
    I assume you mean ST (string theory) rather than SR (special relativity) ? It is true that string theory does not make any currently testable predictions. In that sense it is not falsifiable. I would reserve unfalsifiable for the stronger sense of "not falsifiable in principle"; i.e. whatever technology or techniques are used. Examples are solipsism or last-Thursdayism or Creationism. I would define string theory as untestable rather than unfalsifiable. There have been examples of theories in the past that could not be tested at the time. But later advances in technology (or a better understanding of the theory) allowed tests to be developed (which either confirmed or falsified the theory).
  3. 1 point
    At the beginning of Internet there used to be just server-client communication. i.e. centralized network, server is providing content, and clients connecting to powerful server, and eventually overloading it, because it has to handle too many requests and physically is unable to do so. Later programmers invented p2p. i.e. decentralized network, every peer in network is either server and client at the same time (dynamic and private IP addresses being the most troublemakers) Wireless communication can go this route as well. i.e. every smartphone/device connected to network could be what cell tower is now. For static, the same data, it could be convenient method of decreasing of cell-only communications. F.e. you watch Internet TV channel, device is downloading 100 KB of data, and informing devices around you (within f.e. 100m), "I have 100 KB of file X from offset Y", if owners of these devices watch the same Internet TV channel, their devices ask machine which downloaded data they don't have yet to give them these missing chunks. and immediately sharing (sending, offering to download) them with other peers.
  4. 1 point
    This one. A few important things to note... The expansion of space only happens at very large scales. At the level of galaxies and clusters of galaxies, gravity stops things moving apart. The surface of a balloon comparison only works if you consider the just the surface of the balloon being a 2D analogy for 3D space. This also explains how a finite universe can have no boundary: the surface of the balloon (or the Earth) has a finite area, but has no edge. Dark energy is an extra factor that causes the rate of expansion to increase (this started about 4 billions years ago, I think) The speed at which things move apart is related to how far apart they are. This is nothing special, it is just because expansion is a scaling effect. Consider a number of galaxies separated by the same distance (far enough apart that the expansion of space is significant and the same between all of them). At time 0, they are 1 unit apart: A.B.C.D.E.F After some time they are 2 units apart: A..B..C..D..E..F After the same time again, they are 3 units apart: A...B...C...D...E...F And so on: A....B....C....D....E....F Now, if we look at the distance between B and C, for example, it increases by 1 at every time step. But the distance between B and D increases by 2 at every step. So the distance between B and D is increasing twice as fast as the distance between B and C; i.e. the speed of separation is twice as great. Choose any pairs of galaxies and you will see that apparent the speed of separation is proportional to the distance between them. Take two objects far enough apart and the speed of separation will be greater than the sped of light. (We can see galaxies that are receding faster than light.) We observe that (distant) galaxies are moving away.
  5. 1 point
    Yes...The expansion of the universe affects light and this is observed by the lengthening of the wavelength or shift to the red end of the spectrum, and is known as "cosmological redshift" The actual trajectory is affected by spacetime curvature or warping by intervening objects.
  6. -1 points
    I wont do any of those thing because they are silly.
  7. -2 points
    Does Time Really Exist? I know all physics and chemistry regardless of what you think . You cant just understand me because you are stuck with your math or you dont want to understand .
  8. -3 points
    Well I dont understand why people accept QFT since Relativity and QM are not "physically" connected? This shows how stupid Paul Dirac and all those who continued his work.