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RayYates
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After the big bang, did the cosmic inflation of space occur as a gravitational wave?
How so?RayYates said:It occurred to me that Dark Energy and Dark Matter seem to behave like enormous (galaxy sized) slow moving (relative to light) gravitational waves. Has anyone written about something like that?
bapowell said:Then wouldn't we see periodic fluctuations in the clustering of galaxies?
The dark flow phenomenon refers to the motions of galaxies relative to the background spacetime -- their peculiar velocities. The expansion of space itself, on sufficiently large scales, is uniform in agreement with the standard FRW cosmology. My point about your assertion, is that, if indeed gravity was sinusoidal in space and time, with a wavelength on the order of the size of a galaxy, we would see periodic changes in the strength of galaxy clustering. At first glance, it would also seem difficult to address the fact that structure in the universe is hierarchical -- there are galaxies, clusters of galaxies, and clusters of clusters...RayYates said:There has been work that shows some galaxy clusters seem to be moving together as group (dark flow http://en.wikipedia.org/wiki/Dark_flow) and that the expansion of space is not uniform.
Historically, dark matter was introduced to account for the unexpected galactic rotation velocities. But adding a bunch of dark matter to the universe has other consequences of cosmological significance. In particular, it affects the way galaxies form in the early universe, as well as the amplitudes of the acoustic peaks seen in the cosmic microwave background. These effects are actually in agreement with our latest data from the CMB and large scale structure surveys, and so they provide additional pieces of observational evidence for dark matter. Also, observations of astrophysical events like the Bullet Cluster strongly support the presence of particulate dark matter. So, yes, dark matter was introduced in a rather ad hoc way to explain an astrophysical anomaly. It has since, however, enjoyed additional strong support from a wide range of observations. In addition, particulate dark matter in the form of weakly interacting massive particles (WIMPS) can be rather easily accommodated in modest extensions of the Standard Model of particle physics. In addition, WIMPS fit snugly into early universe thermodynamics, with the correct primordial abundance needed to explain each piece of contemporary evidence.RayYates said:I envision galaxies sitting inside an enormous gravity well, keeping it from flying apart. Dark matter, as a concept, was added to explain this without know what it is.
We determine the geometry of the universe by measuring the location of the first peak in the CMB temperature spectrum. Physically, the first peak tells us the angular size of the observable universe when the CMB was generated. Together with an associated measure of "distance" to this event (provided by the Hubble Space Telescope and other methods), we can test the geometry of the universe with trigonometry.How do we know space-time on (a cosmic scale) is flat?
...WIMPS fit snugly into early universe thermodynamics...
We determine the geometry of the universe by measuring the location of the first peak in the CMB temperature spectrum. Physically, the first peak tells us the angular size of the observable universe when the CMB was generated. Together with an associated measure of "distance" to this event (provided by the Hubble Space Telescope and other methods), we can test the geometry of the universe with trigonometry.
Well, sure! They are hypothetical -- but that's the way science works. They are theoretical proposals intended to explain observable phenomena. We honestly don't know if particulate dark matter is the correct answer, but observational evidence supports this hypothesis and our theories can sensibly accommodate it.RayYates said:Unless I've missed something I though the existence of WIMPS, and other particles like the Higgs boson was still theoretical. Unfortunately I lack the background to comment on the Standard Module.
Distances are typically measured using "standard candles" or standard rulers, not redshifts. Common standard candles are supernovae and other astrophysical structures like the baryon acoustic oscillations seen in galaxy distributions provide a good standard ruler.Would light passing through a gravitational wave would be refracted (as it travels through stretched or compressed space) possibly altering the red shift (distance) and apparent location (direction)?
...Gravity, as a force, can only attract anyways.
Gravity can be repulsive -- it depends on the source stress-energy. Vacuum energy, for example, can be shown to lead to a repulsive gravitational force.RayYates said:Is gravity then always associated with matter, or can a distortion in space-time exert gravity.
Distances are typically measured using "standard candles" or standard rulers, not redshifts.
There is no repulsive force due to a gravitational wave...
Gravity can be repulsive -- it depends on the source stress-energy.
bapowell said:Gravity can be repulsive -- it depends on the source stress-energy. Vacuum energy, for example, can be shown to lead to a repulsive gravitational force.
Indeed. I have in mind the Newtonian potential as a perturbation about FRW. Sorry for the poor language.TrickyDicky said:When in the context of GR it is always better not to talk about gravity as a force (I know it just slips out but it still can be misleading) even if the attractive or repulsive force pictures borrowed from EM are very graphic they are simply not correct in general relativity.
So if we stick to the appropriate modelling of gravity as geometry, yes, a stress-energy tensor source such as vacuum has negative diagonal pressure components.
The tidal force that the + (and x polarized once you do a 45 degree rotation) polarized wave will exert on the ring of dust will operate in a manner such that, if the wave happened to be oriented along the z axis, the rate of change of the x component of the tidal force will be opposite to that of the y component. I would say this is "less" gravity, in your sense of the word, not "negative" gravity.RayYates said:Within the stretched phase, will the matter experience "less" gravity or "negative" gravity?
bapowell said:... our latest data from the CMB and large scale structure surveys ... the first peak in the CMB temperature spectrum. ...
Cosmic inflation is a theory that explains the rapid expansion of the universe in the first fraction of a second after the Big Bang. It suggests that the universe underwent a period of exponential expansion, causing it to grow from a subatomic size to the size of a grapefruit in just a fraction of a second.
One of the main pieces of evidence for cosmic inflation is the observation of the cosmic microwave background radiation. This radiation is the leftover heat from the Big Bang and is nearly uniform across the entire observable universe, suggesting a period of rapid expansion. Additionally, the patterns observed in the cosmic microwave background support the idea of inflation.
Gravitational waves are ripples in the fabric of spacetime caused by the acceleration of massive objects. Inflation theory predicts that the rapid expansion of the universe would have created gravitational waves, which have been observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO). These observed gravitational waves support the theory of cosmic inflation.
The detection of gravitational waves from the early universe supports the theory of cosmic inflation and provides valuable information about the early moments of the universe. It also opens up new avenues for studying the universe and allows us to test other theories, such as the theory of general relativity.
The discovery of gravitational waves has revolutionized our understanding of the universe. It has confirmed the existence of black holes and provided evidence for the theory of cosmic inflation. It also allows us to study the universe in a new way and may lead to further groundbreaking discoveries in the future.