Did photons exist at the singularity of the Big Bang? If they did not, then does that mean that it is impossible to see what happened at the big bang?
[Physics] Photons at the big bang
big-bangcosmic-microwave-backgroundcosmological-inflationphotons
Related Solutions
The Big Bang is a mathematical model of how the observable universe evolved , based on fitting astrophysical observations. Like all models it has its region of validity. When I read cosmology fifty years ago, the model included a singularity at the origin, because that is what the mathematical functions of the General Relativity solutions showed. The model at the time fitted the observed expansion of the universe, which showed clusters of galaxies receding from each other at a certain rate. In that model, all (x,y,z) points at t=0 were at (0,0,0) and it makes no sense to talk outside of this point within this model, a singularity. It was as if an explosion started from the origin, in this model.
It is well known though that when singularities appear in a physics model, it is a sign for the need of an extension of the model or a different model, as happened with the introduction of quantum mechanics for the microcosm of particles, which avoids singularities with the Heisenberg uncertainty principle.
The need for a quantum mechanical framework came from the new astrophysical observations of the last sixty years. The cosmic microwave background observations could not be reconciled with classical thermodynamics within General Relativity. The CMB showed great homogenization, with differences in the temperature map of order of 2*10^-5. This homogenization could not happen at that early time of photon separation, 380.000 years in the history, and quantum mechanics was introduced at the beginning of the universe to homogenize the system.
At the same time observations showed that the expansion of the universe is not constant, a bang and free tracks, but is accelerating and new physics is introduced, dark energy , to explain the phenomenon and still keep a shell of the original Big Bang General Relativity solution.
A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of "inflation" produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light; it also forms a backlight for later developments of the universe.
Now to your questions:
1). As I said, everything was at one point at t=0 in the theoretical model. In the present history there is a quantum mechanical uncertainty as to the region which projects to a point from the classical BB.
2). speculations there are many. The standard physics status is in the picture above
3).is answered by my exposition above
This seems to be a common misconception about the big bang.
At present our theories can only suggest what happened AFTER the "bang". We cannot formulate what occurred AT the singularity with our current knowledge of physics.
At a small neighborhood around a spacetime singularity quantum gravity becomes important and we simply have no clue at present how to deal with the general relativistic singularities (e.g. black holes as well!)
When you hear of physicists talking about the big bang it is almost always a discussion of the dynamics AFTER the singularity.
When physicists discuss what happened during the planck era or at a singularity it is entirely (very) educated guesswork within the bounds of current theory (much like how theoretical physicists like hawking have come up with convincing theories about some black hole properties).
Hope that helps!
Best Answer
You are discussing a cosmological model with a singularity, which is not considered a good model, since when singularities appear in classical physics, and General Relativity is a part of classical physics, quantum effects take over and modify the results. Example the hydrogen atom. Classically an electron and a proton are modeled with a singularity of the potential, 1/r , and classically there could be no hydrogen atom as the electron would finally fall on the proton and disappear. Quantum mechanics solved this by the fixed energy ground level of the Hydrogen atom solution of the Schrodinger equation.
The standard cosmological model still called Big Bang has no postulated singularity at the beginning any longer, an effective quantization of gravity model is used and the quantum mechanical "particles" present in the postulated beginning of the universe are the inflatons.
The inflation period postulated instead of the singularity with quantum mechanical arguments has no photons.
As the universe cools quarks gluons electrons etc appear in a plasma soup , and before symmetry breaking all particles have zero mass, i.e. are photon like. What will develop into photons are the four gauge bosons which are all photon like because their mass is zero.
At symmetry breaking , when the universe has cooled enough, the gauge zero mass particles become the Z W+/- and the photon, so that is the first appearance of the photon as we know it, at 10^-36 to 10^-32 seconds after the beginning of the universe.
We can only model what happened at the fuzzy beginning of the Big bang with the data we can gather. The Ligo data show that we can measure gravitational waves, so that would give us a handle for measurements on the inflationary period, before the electroweak period, if smart enough exeriments can be proposed and devised. At the moment it is with photons that we have a picture of the early universe, and their measurement gave the data that required to model the beginning of the "bang" as an inflationary quantum mechanical period.