noctua Posted January 13, 2015 Share Posted January 13, 2015 I tried looking for a number, but everywhere they just say "FTL" could you help me out with the specifics? Link to comment Share on other sites More sharing options...
Strange Posted January 13, 2015 Share Posted January 13, 2015 Expansion is not a speed. It is a rate of proportional increase in distance. The speed of separation of two points is proportional to how far apart they are. The "faster than light" description of expansion is just journalism. Link to comment Share on other sites More sharing options...
noctua Posted January 13, 2015 Author Share Posted January 13, 2015 Expansion is not a speed. It is a rate of proportional increase in distance. The speed of separation of two points is proportional to how far apart they are. The "faster than light" description of expansion is just journalism. Yet I hear everywhere that nothing can go beyond the speed of light (mostly when talking about matter) But from what i get the speed of light is more or less the speed limit of our universe. Now, there are ways to cheat it, obviously, but I want to find the number, at which the expansion happened if the limit wasn't there, so sort of the layman's speed of expansion. Link to comment Share on other sites More sharing options...
Strange Posted January 13, 2015 Share Posted January 13, 2015 Yet I hear everywhere that nothing can go beyond the speed of light (mostly when talking about matter) But from what i get the speed of light is more or less the speed limit of our universe. That speed limit comes from special relativity, in other words it is only a "local" limit. It doesn't necessarily apply to general relativity. There are (and always have been) galaxies we can see that are receding faster than light. but I want to find the number, at which the expansion happened if the limit wasn't there, so sort of the layman's speed of expansion. I don't really know the answer to this. I think the early value of the Hubble parameter (which is what you are asking about) depends on the amount of matter, energy and dark energy in the universe so may not be known exactly. A quick google shows this: https://www.sciencenews.org/article/speed-early-universe%E2%80%99s-expansion-determined- which says that the rate of expansion 11 billion years ago was 1% in 44 million years. And then there is (hypothetical) inflation, which complicates the picture further. https://en.wikipedia.org/wiki/Inflation_%28cosmology%29 Link to comment Share on other sites More sharing options...
Mordred Posted January 14, 2015 Share Posted January 14, 2015 The greater than c you hear about is whats called the recessive velocity. This is an apparent velocity not an actual one due to inertia. The speed limit is an inertial limit. In expansion there is no inertia seperation distances is simply increasing. Now keep in mind as Strange pointed out the recessive velocity depends on the seperation distance. Hubbles law states the greater the distance the greater the recessive velocity. [latex]v_{recessive}=H_oD[/latex] Locally and everywhere the rate of expansion is 70km/Mpc/sec However recessive velocity depends on the measurement distance. At roughly 4239 Mpc (Hubble sphere ) the recessive velocity is 1 c, at the furthest we can see it's 3.2 c However to the first Mpc from us it's only 70km/sec. If you could teleport to the furthest observable distance. The measurement would be the same for the first Mpc 70 km/sec. Inflation is calculated by number of E folds and the number depends on the inflation model. More than 60 Link to comment Share on other sites More sharing options...
cosnut Posted March 11, 2015 Share Posted March 11, 2015 What happened in the beginning is still much of a mystery - and may always be. If you assume the velocity distance law represents real changes in velocity of nebula, then you can use it to get an estimate of what is happening at the present. For an accelerating universe H can be taken as invariant in which case since v = Hr, then dv/dt = H(dr/dt), but at the Hubble sphere dr/dt = c, so dv/dt = Hv = c^2/R If the same formula applied near the beginning the initial expansion rate would be very large owing to the small size of the universe - in some theories expansion rates are many times that of light during early epochs. But the STR does not apply to expansion velocities inasmuch as the nebula are considered to be commoving with space Link to comment Share on other sites More sharing options...
Airbrush Posted March 11, 2015 Share Posted March 11, 2015 How many light years is an Mpc? Most people are not familiar with Mpc. Link to comment Share on other sites More sharing options...
Strange Posted March 11, 2015 Share Posted March 11, 2015 3,261,633.44 light years Link to comment Share on other sites More sharing options...
Spyman Posted March 11, 2015 Share Posted March 11, 2015 1 Megaparsec (Mpc) is roughly 3.26 million light years. A parsec is the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond (the diagram is not to scale). http://en.wikipedia.org/wiki/Parsec Link to comment Share on other sites More sharing options...
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