guenter

E.g. photons, neutrinos Uncharged particles don't annihilate with their antiparticles.

imatfaal, the homogeneity of the CMB (the temperature variation is around 10^-5) originates from the thermal equilibrium of the plasma at that time. This excludes annihilation radiation areas.

No, at least not according to the present knowledge. The matter including dark matter exceeds the matter of the black holes by far. Further, the microwave background shows no signature of matter-antimatter annihilation.

Justin, interestingly there are two possibilities. In both cases the scientists in this research are relatively optimistic: Primordial gravitational waves can in principle be detected as a signature in the microwave background (ongoing research of Planck) or as radiation reaching us today by interferometer techniques, e.g. LIGO ect. The microwave photons have been emitted 380000 years after the big bang (before the universe wasn't transparent for them), primordial gravitational waves however were created very shortly after the big bang (for them the universe is transparent), thus providing hopefully direct information about the early universe.

Misunderstanding. Here Wiki explains 'orbit decay', Justin's question however was "do gravitational waves decay over time?" in the context of primordial black holes. There aren't even massive bodies whose orbit could decay.

Justin, you are right, as reportet here: I am not sure what you mean with "decay". Like electromagnetic waves gravitational waves too get redshiftet while the universe expands. DrRocket, the strongest signals are expected from the merger of massive objects, neutron stars, black holes. Unfortunately such events are rather seldom.

No one says this. It might be advisable to read the "Overview" in Lambda - CDM model.

During the merger of black holes gravitational waves will be emitted, not electromagnetic waves. The latter depend on electric charges. But there are none, if you disregard the accretion disk.

What happens to the infalling matter finally is not known. Besides being compressed it is also exposed to high tidal forces. Matter-Antimatter-Annihilation however seems rather unlikely, because Antimatter doesn't fall in as far as we know. But its an interesting question, whether under high energy conditions (like in the early universe) the conservation of the baryon number could be violated. Has someone an idea?

The early universe expanded extremely fast. This might have limited the growth of the primordial black holes. Its just a guess. In addition to that, the redshift of the CMB photons tell us that the universe expanded by 1100 times since their emission.

This is a weird discussion in a physical forum. It is unphysical to expect matter being radiated away. Should someone be interested in Physics, this is the right explanation, which coincides with my post #8.

In deed, the masses of the elementary particles are considered as physical constants.

The term null-geodesic means the light-like path of a photon. Background: The space-time intervall for a photon is zero. You can easily search for that in Wikipedia, to lern more. I will not comment anymore, because its off-topic. MODERATION: Is it possible to contact an expert in GRT/Gravitational waves, who could clarify my questions? I appreciate any help. Thanks, guenter

According to General Theory of Relativity the sign of the curvature parameter k depends on the ratio total energy density / critical density = Ω. The curvature determined by this means the local curvature, which is important to know. And since the cosmological principle is the foundation of the FRW-model it follows that the local curvature is constant, means it is the same on each place in the entire universe. To avoid a possible misunderstanding: Imagine the torus e.g., which is one of the 5 possible topologies in case k = 0 (flat). The torus as a whole looks round, however is flat locally everywhere. It is thus advisable not to mix up geometry with topology. GRT says nothing about the topology, but there is a chance to detect it via the CMB. Why are most of the cosmologists convinced that the universe is locally flat (see above), inspite of the uncertainty of Ω? If Ω would have been even very slighty >1 before inflation, then the entire universe would have collapsed within seconds and in the case of Ω <1 (even slightly) it would have expanded so fast that no galaxies could have been formed, because it is a slow process. This one has to believe as a result of the einsteinian equations. The conclusion is that the early universe (entire) was by a factor of 10^-15 closer to Ω = 1 than today (cosmologist G. Hasinger). Sorry, I don't understand this point. Perhaps the above clarifies it.

Supposed Ω = 1.02 exactly (what we don't know), then it seems (almost flat) here in our observable universe and also in other arbitrary places thereout, because the value is close to 1. But infact it would be spherical, yes. Sorry, I am in a hurry and will come back to your post later.

Let me try. Wikipedia says: "The WMAP data are consistent with a flat geometry, with Ω = 1.02 +/- 0.02" This is in agreement with Paul Davis. There is a very slight possibility, that the universe isn't flat, it could be a hypersphere. The majority of the cosmologists expect exact flatness however. They are arguing there should be a specific reason for that and that is inflation. It is very unlikely to arrive at Ω = 1.02 after blowing up the universe by a factor of 10^30. The Planck mission will increase the accuracy of Ω, then we know more. So, Davis argues correctly with a lack of accuracy. He doesn't say the universe can be flat here and spherical or hyperbolic there. His message is, if it seems flat here then it still could be spherical. And of course, the larger the assumed radius, the lesser one can exclude spherical geometry, even in case Planck would yield Ω = 1.001 +/- 0.001. If your claim that the cosmological principle applies only to the observable universe was correct, then why are cosmologists writing papers concerning the topology of the universe, the global structure of the universe as a whole? This wouldn't make any sense, if the cosmological principle wouldn't hold for the entire universe. But, it seems, I repeat myself. It is the Copernician idea, that the observable universe isn't special. On the other hand, you can stay with your claim, why not. The standard cosmology is based on more or less plausible assumptions. In my opinion nobody can proof that you are not correct. Should you identify papers which support your claim, I would be interested.

There is a way, Anilkumar. The Friedmann-Robertson-Walker cosmological model is derived from the einsteinian equations. Here the mass density is thought homogeneous like sugar in the tea. Being perfectly structureless, the curvature as expressed by the sum of the angles in a triangle can be hyperbolic, euclidian or spherical. Depending on the mass density. @IM Egdall: "As to why mass/energy causes the warping of spacetime -- I think we need new physics to answer that." Why? There is no need, as long as the predictions of the theory are in excellent agreement with the observation. The problem of General Relativity is the singularity.

Ω = Ω_M + Ω_lambda = 1 over time, whereby Ω means the resp. energy density / critical density. Sorry, I can't write the correct symbols. The microwave background revealed Ω = 1 (universe is flat) and Ω_M = 0.3 (roughly). So, an important contribution Ω? = 0.7 was missing. To detect this missing energy, later called dark energy, by analysing supernova Ia data independent of the CMB in the wright amount was a tremendous success. From this it should be clear that the ratio Ω_M / Ω_lambda was very large in the past and will be very small in the future. In case you talk about chaotic inflation, meaning various universes, then you can expect a variation of geometry from universe to universe. However this is highly speculative and not standard cosmology.

Look here : and It would be meaningless to talk about a 3-torus-topology (signature of WMAP data) of the universe, if the cosmological principle wouldn't hold for any location on the torus, including our observable universe.

Replacing the rocket by radar signals, we talk about the Shapiro Delay. Those signals reflected by mars take more time to return to earth in case they pass near by the sun than compared to an analogous measurement without the sun. The effect is tiny but measurable and demonstrates the spacetime curvature due to the sun.

No, because according to the cosmological principle (FWR-cosmology), the local geometry is the same in arbitrary locations in the universe. Using PorpoiseSeeker's wording, if it is flat here, it's flat there. But one should keep in mind, that the cosmological principle is an assumption.

They are the distortions carried when matter will radiate. Needless to say, a large amount of time is required before matter will radiate away in the form of gravitational waves. Gravitational waves are transverse waves like electromagnetic waves (and water waves). Matter will not be radiated away. A binary neutron star e.g. looses gravitational binding energy while emitting gravitational waves, which results in an orbital decay of the system. Finally the stars are coalescing due to the loss of angular momentum.

Yes, nobody can exclude the possibility that the observable universe is a special place. However the standard FRW cosmology seems more likely.

Where is the path from the null geodesic to my questions? Perhaps these are non trivial.

Ω_M and Ω_lambda can vary with time. However their sum, the density parameter Ω = Ω_M + Ω_lambda = 1 over time. So, the universe had, has und will have euclidian geometry.