I'm wondering whether the residual light of the Big Bang comes from one particular direction and what possibilities do we have to detect its position?
[Physics] Where does the light of the Big Bang come from
big-bangcosmic-microwave-backgroundcosmologyelectromagnetic-radiation
Related Solutions
In the context of FRW cosmology, there is no difference in the rate of time between the epochs of the evolution of the universe. You can see that from the form of the line element
$$ds^2=-dt^2+a(t)^2\gamma_{ij}dx^idx^j.$$
That is a result of the symmetries that you assume for the matter distribution (homogeneous, isotropic) and the choice of observers that you make. So the observers that follow the expansion of the Universe, which are the galaxies more or less, perceive the same time wherever and whenever they are. The cosmological time is the proper time of all the comoving observers, as it is evident from the line element.
In the case of a Schwarzschild metric and static observers
$$ds^2=-(1-\frac{2M}{r})dt^2+(1-\frac{2M}{r})^{-1}dr^2+r^2d\Omega^2,$$
it is the factor in front of dt that makes the difference and you have different time rates for observers at different positions.
There is one more point. Someone mentions the redshift and the perceived difference of the rate of time for faraway objects. That would appear to contradict what I am saying, but it isn't. The redshift effect is an observer symmetric effect. Like in the case of SR where you have two inertial observers with different velocities and each of them thinks that the others time runs slower, when both of them actually experience proper time. That is very different from the case of the static observers near a gravitating object, where there is no such symmetry. The clock of the observer that is at bigger r runs faster than the clock of the one that is at smaller r.
Spacetime (probably) does indeed have at least one boundary. Crazy Buddy mentioned three related questions in his comment, and reading these will help you understand why spacetime has a boundary in the past i.e. the Big Bang. This is a singularity and it is a boundary because you cannot follow geodesics back through it to earlier times.
If the universe were closed (the experimental evidence is that it isn't) then there would be a similar boundary in the future i.e. the Big Crunch. This time it would be impossible to follow geodesics forward through the Big Crunch to later times.
In some of the theories of dark energy future boundaries may exist even though the universe is not closed. In particular there is a possible singularity called the Big Rip that would also act as a future boundary. However I should emphasise that these theories are highly speculative.
All the above boundaries are ones that co-moving observers hit by travelling in time. If you're asking if the universe has a boundary in space, i.e. there is a point where some observer could not move in that spatial direction, then as far as we know there are no such boundaries. If the universe is currently infinite then it has always been infinite. Alternatively if it is closed (presumably on some scale much large that the observable universe) then there would by definition be no edge.
On last caveat: I would guess most of us don't believe singularities exist, and some theory of quantum gravity will take over at very short distances and remove the singularity. This would also remove the boundaries I mentioned above. However no such theory of quantum gravity exists at the moment.
Response to comment:
It's a common misconception that the Big Bang was a point where everything came into existance, and therefore that the expanding universe must have an edge because it expanded from a point of finite size. However this is not the case. There are two possibilities:
- the universe is closed on some very large scale.
In this case consider the analogy of a balloon deflating. A (very small) ant crawling on the balloon would never encounter an edge as the balloon shrinks, so there would be no boundary. The Big Bang is analogous to the point where the ballon shrinks to zero size. What happens at zero size we can't say (because this is a singularity) but at any non-zero size, no matter how small, there is still no boundary.
- the universe is infinite
This is harder to stretch your brain around. If the universe is infinite then it has always been infinite and remains infinite in size even back to the Big Bang. At the Big bang you get the odd result that the spacing between every point in the universe is zero, but the universe is still infinite. But then this is what makes the Big Bang a singularity. Whatever the case, like the closed universe for any non-zero size, no matter how small, there is still no boundary because the universe is infinite.
Best Answer
By "the light from the big bang", you must mean the cosmic microwave background, which did not come from the big bang directly, but was emitted during recombination about 400,000 years after the big bang. At that time, it was emitted from basically all directions and locations in space. The universe was born hot, and cooled gradually as it expanded, meaning the photons were becoming gradually less energetic. Photons and matter in the universe were interacting constantly, and light could not travel very far before interacting with protons and electrons and changing direction. Electrons and protons were also coming together to form neutral hydrogen atoms, but these were quickly dissociated by photons.
The cosmic microwave background was emitted when there were no longer enough photons with sufficient energy to break neutral hydrogen apart in to free protons and electrons. Once this became true, photons just kept on traveling in whatever direction they were going, without interacting. As this happened everywhere in the universe at just about the same time, you can see light that is part of the cosmic microwave background from any point in the universe, that will happen to show you light that is 13.7 billion years old (the time in the past when the cosmic microwave background was emitted).