"cosmic bruises" as evidence for the multiverse

[noons]

So I've done some reading about theories concerning the multiverse and inflation theory. One such theory basically states that universes are constantly popping into existence, and occasionally "bump" into each other. According to the theory, these collisions would leave "cosmic bruises" in the background radiation. Apparently, such "bruises" have been found in the last few years, and the new European Planck Satellite should be able to give more accurate readings this year.

Has anyone else read anything about this?

[bvgdez]

I see no-one has replied to this yet. I can't help either but I can throw in a couple of related questions. Maybe someone else ( I believe James is a physicist) can shed more light on this?

While I was over in England last week I happened to watch a programme entitled "How Big is the Universe?" in which this theory or hypothesis was put forward.
I had always thought that each universe creates its own space so to speak, i.e. that it's wrong to think of a universe coming into existence within space. If that's the case, how can two universes share the same space? (which would be a prerequisite for a collision, wouldn't it?).
And assuming they can occupy the same space then would the fact that our universe is surrounded by others explain why the expansion of the universe is accelerating (as the gravity from other unverses pulls our one towards the others)? Probably not, as I have a very patchy grasp of cosmology but I do find these questions really interesting.

[sankari]

I'd like to contribute, but unfortunately this entire topic is beyond my comprehension.

[Mike D]

I'm a bit of a n00b (as the young people would say) in this area too: after seeing the OP, I did a little reading. And for what it's worth, my thoughts on this are:

1. It feels strange (to me) describing this as evidence for multiverses: the whole idea that something could be described as 'another universe' if it can actually physically affect this one (even to the extent of altering background radiation) seems counter-intuitive.

2. It may all be apparent patterns in the data that turn out to be random fluctuations. A quote from www.technologyreview.com/view/421999/astronomers-find-first-evidence-of-other/:

So, what to make of these discoveries. First, these effects could easily be a trick of the eye. As Feeney and co acknowledge: "it is rather easy to find all sorts of statistically unlikely properties in a large dataset like the CMB." That's for sure!

There are precautions statisticians can take to guard against this, which both Feeney and Penrose bring to bear in various ways.

But these are unlikely to settle the argument. In the last few weeks, several groups have confirmed Penrose's finding while others have found no evidence for it. Expect a similar pattern for Feeney's result.

3. Given that evidence of *something* has been found in the background radiation, why do some physicists believe it evidence of universes bouncing off each other? Are there any competing theories to explain this result, assuming the result is real?

[ignorantianescia]

Because the improbably low entropy of the universe is one of the fine-tuning problems, sometimes a high entropy multiverse with smaller low-entropy universes inside as small scale decreases in entropy is suggested as a solution (though it leads to the notorious Boltzmann brains problem, though some theories seem to avoid it). Maybe that is the idea they were talking about? Otherwise I can only agree with everybody else.