Strange

But are you thinking of the start of expansion, or a change from a collapsing to an expanding universe? Or something else? To my mind, these are just stages or changes in the evolution of the universe rather than the unique "creation" event many people seem to use "big bang" to refer to.

To avoid going round in circles, what do you think such an event could be?

And there isn't really any good reason to think there was any such event. Hence even more confusion!

Surely, it is the distance between the source and the mirror that needs to meet this condition?

Maybe we are talking slightly at cross purposes here. I am not trying to make a distinction between the model and reality (although that is an important to distinction to keep in mind). Rather, I am trying to make a distinction between the (arguably incorrect) use of the term "big bang" to refer to a one-off event which is popularly described as an explosion or creation of the universe, versus the use of "big bang" to refer to the way the universe evolves over time. I agree that is a perfectly valid question and an active area of research. So, ultimately, you are right: it is just a matter of words. I just happen to think the common use of the words "big bang" is, or can be, very misleading.

No use at all. That's the point. The big bang model says nothing about what happens then. Of the universe and, more specifically, how it evolves over time. This is part of my problem with the phrase "before the big bang"; does it mean "before the universe"? If so, why would anyone think there was anything before the universe? By which I mean, why would anyone think there was a time when the universe didn't exist (in some form)? Maybe. But I am always worried when people seem to be referring to "the big bang" as an event (rather than a process or a model). Right. But there is no reason (as far as I know) to think there is a "beginning" (other than t=0 in the current big bang model, which we agree probably doesn't represent reality).

Can you provide a reference to this "Silvertooth Experiment"? All I could find was mentions on various crank science and conspiracy sites.

The singularity at t=0 is sometimes described as "the math breaking down". But it is, perhaps, more accurate to say that the theory no longer works (provides meaningful results) at that point. All theories have a limited domain where they are valid. You tend to get invalid results when you go outside those limits. I don't think anyone doubts that. But it is the only one we have! The big bang is a model (cosmology based on the FLRW metric, commonly described as the Lambda-CDM model). It isn't a "thing" or a point in time. So if there was a "big crunch" then that would be part of the same model. If the universe is infinitely old (which some attempts to merge quantum theory with GR suggest) then that would be part of the model.

I don't think it would answer the question. Even if half the dark matter was dark-antimatter because the problem isn't just "why isn't (*) there as much matter as matter, but "why aren't there as many anti-electrons as electrons, as many anti-protons as protons, etc." If these particles were formed from the initial conditions of the universe, then you would expect them to be formed in matter-antimatter pairs. (*) The question is, I think, more accurately, "why wasn't there an equal amount of antimatter" because if there had been, then it would have all annihilated and we would live in a universe made almost entirely of photons. Or rather, we wouldn't.

I guess I don't really understand what people are asking when they say "before the big bang". It sounds as if they are referring to the big bang as an event (which it isn't). The only thing I can think of which, theoretically, counts as such an event is the idea of the singularity at time zero. Even though this is probably not physically realistic it is still the only scientific theory we have. (There are all sorts of hypotheses and speculations about how to remove the singularity but none are confirmed or generally accepted yet.) If by "before the big bang" people just mean "before the earliest known hot dense state" then I agree the question make sense (it is just badly phrased).

How long have they been bombing Syria?

Refugees are migrants (but not all migrants are refugees). Millions fled Syria due to its civil war and the rise of IS, long before "we" got involved. No. Evidence? The overwhelming number of refugees from Syria (and neighbouring countries caught up in the conflict) have stayed in places like Lebanon and other middle-Eastern states. So your argument doesn't hold water.

It didn't "start". It is pretty well understood that there is a singularity at t=0 in the FLRW metric. If you are claiming otherwise, it is up to you to support that claim. More discussion here, if you are interested: http://physics.stackexchange.com/questions/151027/interpretation-of-a-singular-metric "the FLRW spacetime is a combination of the manifold [math]\mathbb{R}^{3,1}[/math] and the FLRW metric [math]g[/math]. The metric [math]g[/math] has a singularity at [math]t=0[/math] because at that point the proper distance between every pair of spacetime points is zero."

In classical GR there is a singularity at t=0, therefore the is no "before". If there is no singularity then there is no "time zero", no "first event" and therefore there is nothing to be "before". Either way, I can't see that the question makes sense. As to how you would test it: hopefully a theory of quantum gravity would make some predictions about what to look for on the CMB (or elsewhere) to confirm its predictions. For example, Penrose has claimed that there are patterns in the CMB that confirm his ideas.

But the question still doesn't make sense; if there was no starting point, then what does "before" mean? Before what? Is the question just "what happened earlier than the earliest time we know about"? In which case, the answer is a rather obvious "we don't know (yet)".

In the mathematics of GR there is a singularity at time t=0. That is roughly equivalent to a pole: in the same way that the lines of longitude converge at the north pole and go no further, space=time converges at the singularity and goes no further. Of course, most people don't think that the singularity represents physical reality. We probably need a theory of quantum gravity to better understand the universe at that stage. It may turn out that there was no "big bang" in the sense of an initial starting point. The universe may be infinitely old. Or it may have collapsed and re-expanded. Or it could have been in some unknown state prior to expanding.

So that explains why bricklayers are driving round in gold-plated Ferraris and bankers are living on the breadline.

Not really, I am talking about how the universe is described in GR (i.e. the big bang model). There are various estimates of how much bigger than the observable universe is the whole universe is. Based on the flatness determined from the CMB, it is thought to be at least 150 times larger than we can see. On the other hand, it might be infinite.

OK. Putting aside science means you can choose whatever answer you want. But, based on the images we currently have of atoms and molecules, a hydrogen atom would look like a fuzzy sphere of cloud. And it wouldn't radiate anything. Unless it had absorbed a photon, in which case, it would enit it again some time later.

You need to explain that. It is pretty meaningless unless you tell us what they symbols mean. And what the evidence or theory is for this structure.

Asking what was "before" the big bang is like asking what is further north than the North Pole. It doesn't really mean anything. It isn't expanding into anything. The universe is all there is.

Well, really, just for dramatic effect! But you could interpret that as his "present" changing around him as his past actions catch up with him. Or that he is slowly being pushed from one timeline to another. But any of these explanations only make sense in terms of the world that is created in a particular story or movie. All one can expect is that the storytellers remain consistent with their own assumptions and conventions.

It would be better if you used Google Translate because you have no ability to write in English. "Sería mejor si usted utiliza el Traductor de Google porque no tienes capacidad de escribir en Inglés." https://translate.google.com/

I wonder if (i) and (iii) are actually any different - in terms of what is perceived. Taking Back to the Future as the canonical example, is it possible to distinguish between being in the same timeline that has changed versus a different timeline? Maybe Marty et al. actually ended up in a different universe but then managed to get back to the original one (or one very similar to the original). All of these can create great fiction. Case (ii) is used in several stores, for example Twelve Monkeys and the gag in Bill and Ted where they hide a key for their earlier selves to find so they can escape from the police station. Bill and Ted also introduces the paradox of where information comes from: the only way that Bill and Ted know Rufus's name is because the future Bill and Ted tell them. How do the future Bill and Ted know, because they were told by Bill and Ted. But maybe his name isn't Rufus at all ...

I have no idea. You certainly haven't shown that there is one. There is a contradiction in those two statements. So which is it? Also, simply repeating this assertion does not make it true. How about some evidence? Why? Maybe he thinks it is good idea for people to look after each other. Maybe he thinks it is good to reduce the population. He told me that He thinks you are wrong.