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wolram
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Is the red shift evidence enough to define accelerated expansion
CalcNerd you have confused expansion and acceleration.CalcNerd said:Yes.
While Professor Hubble did find some galaxies were drifting towards us, most were moving away. And the farther these galaxies are from us, the faster they were moving away as determined by their red shift. Hence proof of an expanding universe.
Like most things, it's a combination of observations. The primary pieces of evidence are supernova surveys, baryon acoustic oscillation observations, cluster surveys, estimates of ##H_0## from relatively nearby, and the CMB.wolram said:Is the red shift evidence enough to define accelerated expansion
The expansion rate is not a speed. Superluminal recession velocities are admissible because special relativity applies only locally in the universe: two receding galaxies (comoving with the expansion) are in separate inertial frames.Quds Akbar said:Yes, the space between us and galaxies might be expanding. And some galaxies are moving away from us faster than the speed of light because the space in between us and them expands and the speed limit does not apply to the expansion of space itself.
Accelerated expansion of the universe is not related to accelerated observers in special relativity.slatts said:The difference between acceleration and non-accelerated motion is often neglected by people interested in physics, but The Stanford Encyclopedia of Philosophy (available online) points out the fact that, in the view of the philosopher and physicist Sklar, acceleration is the most mysterious component of relativity.
slatts said:Since Andromeda's the galaxy nearest our own, he plainly sees them as being in the same inertial frame, and you don't see that even as a possibility.
slatts said:He attributes, to S R, significant effects on the simultaneity of events in "a nearby galaxy" that result from infinitesimal changes in the local velocity of an observer here.
PeterDonis said:He's not describing our actual universe in this thought experiment; he's describing an idealized universe in which SR is valid even on large distance scales. In our actual universe, it's not. For the purposes of his thought experiment, the difference doesn't matter; but the fact remains that it's an idealized thought experiment only.
the red wavelength indicates that light is going away from us but on large scale it becomes game of time .if something in definite room goes away from us doesn't means that always room is expanding it might be the acceleration of object otherwise something unknown is working.am not sure about anything also not proving wronge anything because the expansion of universe is not totally proof.wolram said:Is the red shift evidence enough to define accelerated expansion
slatts said:(This crossed the reply by PeterDonis:) I understand that they are moving relative to each other (-in fact, I think I've heard that they're heading slowly toward a collision), so I'd figured that where Greene and Bapowell might be disagreeing is on whether Special Relativity applies to events in different inertial frames.
It's possible, alternatively, that Greene has (or had) a much broader view of the approximations adequate for the consideration of objects as being in the same inertial frame.
Greene's book's not free online, but the example, illustrated in its notes with "the usual concept of spacetime diagrams [italics his] taught in courses on special relativity" and including a relevant example of one, shows how a change in the direction taken by an observer walking (yes, walking) on a planet in Andromeda changes those earthly events which are simultaneous with his walk from events that are decades old in Earth's past (when the observer's walking further
PeterDonis said:He's not describing our actual universe in this thought experiment; he's describing an idealized universe in which SR is valid even on large distance scales. In our actual universe, it's not. For the purposes of his thought experiment, the difference doesn't matter; but the fact remains that it's an idealized thought experiment only.
slatts said:does anyone familiar with the concepts involved think this might be a possibility?
The evidence for an accelerated expanding universe comes from several sources. Firstly, observations of type Ia supernovae, which are a type of exploding star, have shown that they are dimmer than expected. This suggests that the universe is expanding at an accelerating rate, as the light from these supernovae has had to travel a longer distance to reach us. Secondly, measurements of the cosmic microwave background radiation, which is the leftover radiation from the Big Bang, also support the idea of an accelerating universe. The patterns and fluctuations in this radiation indicate that the universe is expanding at an accelerating rate.
The evidence for an expanding universe comes from the observation that galaxies are moving away from each other. This was first discovered by astronomer Edwin Hubble in the 1920s. By studying the light emitted from galaxies, he found that the light was shifted towards the red end of the spectrum, indicating that the galaxies were moving away from us and each other. This phenomenon, known as redshift, is a result of the expansion of the universe.
Dark energy is a mysterious force that is thought to make up about 70% of the universe. It is believed to be responsible for the accelerated expansion of the universe. However, its exact nature and origin are still unknown and continue to be a subject of research and debate among scientists. Some theories suggest that dark energy is a property of space itself, causing it to expand at an accelerated rate.
There are several theories that have been proposed to explain the evidence for an accelerating universe. One of these is the theory of modified gravity, which suggests that the laws of gravity are different on cosmic scales and can account for the observed acceleration. Another theory is the presence of a cosmological constant, which is a constant energy density that exists throughout space and causes the expansion of the universe to accelerate.
The Big Bang theory, which is the prevailing model for the origin of the universe, suggests that the universe began as a hot, dense singularity and has been expanding ever since. The idea of an accelerating universe fits into this theory by providing an explanation for the observed expansion of the universe. It suggests that the expansion is not slowing down, as previously thought, but rather is accelerating due to the influence of dark energy or other factors.