Expert: Courtney Seligman - 12/3/2010

Question
Hi Courtney, some further points,if i may. You gave me a run-through of quantum mechanics,which i understand fairly well. Forgive me, but i felt you didn't answer my specific point about this as mechanism for the bb. Quantum mechanics is a feature of 'our universe'. IS IT SCIENTIFIC for us to offer this as a possible cause of the bb, whether its many bbs or not etc. Many physicists, through the media, tell me as a layman, that i cannot offer any comments on a pre-bb era-it is 'senseless and unscientific'. Yet many physicists do offer explanations! Which is it? Admittedly they can make a far more educated 'guess' than me but what im asking is the principle. The following statement may look petty-i don't mean to be. When i open a can of coke, the pressure release causes many bubbles. Could a similar mechanism have been the cause of our bb (being one of those bubbles!). Please don't answer this question-it is not a serious question. Its just to illustrate my point. By saying quantum mechanics may be a cause of our bb, are we not just taking a phenomenon in our universe to explain an event in pre bb 'space', that may not even have had quantum effects, as we know them? If we accept a bb, do we not have to accept that we will never know what caused it? Would you agree that physicists have more readily accepted that we fundamentally cannot know all quantum states (momentum position etc), better than, we cannot fundamentally know pre bb (or pre planck time)events. Physicists seem to have readily accepted a limit to knowledge in one area but not another. To summarise, a quantum fluctuation causing the bb is pure guesswork?? Thankyou once again Courtney for your time Regards Richard.

Answer
(Sorry about the delay in answering you. I've been swamped with work for a project that was due today, and just haven't had time to check my personal mail.)

It seems to me your question is, can we be sure that the physics we presume to be true in our Universe would have also been true in a previous Universe, so that the argument I made in my previous answer might be correct.

The answer to that would be no, we can't. In fact, there is a subset of physics (which in times past would have been called metaphysics) which covers such questions as, Are the laws of physics required to be the way they are, or could different Universes have different laws of physics? The answer, depending upon whose theories sound most reasonable, is yes, no, or maybe.

Since we don't know why the laws of physics are the way they are, it is possible that other Universes could have different laws. Presumably they would be similar in some ways, in that whatever the laws are they are the same everywhere and at all times in a particular Universe, but different in the details. The question is usually amended by asking, if the laws were different, would there be anyone around to notice it? That is, would life (or stars or planets) be possible, in a Universe with different laws of physics? If the only way for someone to be around to notice what the Universe is like is for it to have the laws of physics that our Universe has, then there could be Universes that have different laws, but no one would notice. (I think I put that correctly, but the statement is inherently redundant, so I may have overstated it.)

At any rate, there would seem to be a few possibilities:

(1) All Universes do have to have the laws ours does, so the previous answer was more or less correct.

OR

(2) Different Universes could have different laws, but for our Universe to have sprung from such a prior Universe, its laws must allows the creation of new Universes, in a process at least vaguely similar to the previous answer. (If not, they would be "sterile" and produce no new Universes, which would make them irrelevant to the discussion.)

If (1) is correct, then all Universes are sort of like ours. If (2) is correct, then the infinity of Universes could have a large number which produce no new Universes, and a large number which produce new Universes, of which some (such as ours) would have lifeforms wondering about this sort of thing, and others (with laws which do not allow for lifeforms) would exist without observers, leading to the question "If a Universe has no observers, how can you tell if it exists?" Which isn't as silly or as profound as it might sound, since we can't tell if any other Universes exist, as it is.

In other words, you are correct in assuming that we can't really know the laws of physics in whatever Universe led to ours. We can say that a Universe such as ours should produce an infinite number of new Universes, but we can't say what any of them would be like, just that they must spring into being and simultaneously cease to have any connection with ours. So going forward, things are very uncertain. And going backward, they are even more uncertain, as all we can say is that the CBR has characteristics which appear to agree with calculations of what the early Universe should look like if it came into being in the way I described earlier. But that doesn't tell us anything about the nature of the Universe from which ours sprang, save that it must have been capable of creating new Universes.

At this point, it feels like any further discussion on my part (without further query or input from you) would be meaningless rambling, akin to medieval arguments about the number of angels who can dance of the head of a pin -- the answer presumably being, whatever number God chooses to allow. In the same way, the correct answer to the origin of the Universe is probably whatever the Universe(s) "choose" it to be, based on the laws of physics which govern(ed) them. My previous answer was based on what we know of physics here and now. I would like to presume that the correct answer isn't infinitely far from that one, and I presume the physicists you discuss would like to presume the same thing. But as the song said, "It Ain't Necessarily So"...