“Multiverse is a concept which we know frighteningly little about”: These words by Doctor Strange to Peter Parker in the recently released Spider-Man: No Way Home is not absolutely incorrect. Last week, too, the teaser for Doctor Strange In The Multiverse Of Madness also shows this concept of multiple universes.
So, is there any scientific backing to this fantasy? Though some physicists have proposed that our universe may just be one among multiple realities, others say that this is nothing but speculation.
Sabine Hossenfelder, a German theoretical physicist had an interesting take on the multiverse. In a video published in 2019 on her YouTube channel, she says that “believing in the multiverse concept is logically equivalent to believing in God. Therefore it’s religion, not science”. She explains that science does not tell us anything about universes we cannot observe.
To understand more about this, indianexpress.com spoke to Dr Kinjalk Lochan, Assistant Professor of Physics at IISER Mohali, who specialises in the fields of general relativity, black holes, and early universe.
Most physicists say that the concept of multiverse is speculation or science fiction. Then, why do some believe that it might exist?
Let me infuse some optimism for the sake of discussion, without committing to being a supporter of the concept. With the advent of quantum mechanics, there came a wonderful insight — that it is unimaginably difficult to completely rule out something. Every process has some probability of occurrence — low or high — but seldom zero.
Whatever we usually see, learn and fathom is based upon experiences we have — experiences gained at the scale (of size and energy) we typically live in. There is usually a well-understood flow of events from which we deduct some inferences as per logic. For example, if a person stands in front of me, I will infer that he/she is not at any other place at that time.
At the microscopic level, however, two or more realities may coexist — an electron, for example, may simultaneously live “here” and “there” (proven by experiments). The famous Schrodinger’s cat example shows that the cat may simultaneously be dead and alive if it gets coupled with a microscopic particle whose being “here” or “there” either kills the cat or spares it.
These concepts lead to the idea (speculations if you may like to call it) that when the universe was born, it was also a microscopic entity. Hence, it must also have had a million possibilities to coexist in. The question is what happened to those other possibilities? Did they fade away in favour of the one we see or all of them do really co-exist? I dare say we do not know for sure.
Are there any published scientific papers about this concept?
The idea has been around for many years in one form or another. Some think that this idea has its roots in the famous paper on the many world interpretation of quantum mechanics by Hugh Everett III (1957) where he proposed quantum systems do not collapse to one reality but continue to live with different “worlds” capturing different realisations.
Similar ideas later appeared in various forms in terms of the existence of multiple “vacua” (initial seeds of the universe) in theories such as chaotic inflation and string theory among others.
Many famous scientists like Leonard Susskind and Andrei Linde seemingly vouch for its existence.
If we are in a multiverse, shouldn’t different universes interact? Wouldn’t we see some effect?
This is a very pertinent question with no clear and acceptable answer for everyone. We know that the microscopic systems indeed simultaneously live all the realities and those realities do interact — interference being a buzzword for that.
However, somehow, when the systems grow larger, the interference disappears as we do not see it in our daily lives — possibly through a mechanism called decoherence.
Whether the many worlds of the multiverse — if they exist — have decoherred (undergone decoherence) enough as the universe expands and grows is not clear theoretically.
Can LIGO, Webb or newer advances help shed light on this question?
The scientific mandates of the advanced experimental proposals being run now or proposed in near future are not for testing the multiverse. They are precisely designed to carry out experiments that shed light on some unknown aspects of scientific queries within this universe.
Having said that, such experimental runs often get some spurious signals, something they were not looking, thereby opening the horizon for other possibilities. However, I do not imagine people will run to a “multiverse explanation” for any of them so easily as there are still so many things within our universe that need proper understanding.
I’ve read that a certain Copernican principle shows that a multiverse is possible. Is it true?
The Copernican principle suggests that in the universe, no position or frame is special, including that of the Earth. So there is no special condition that miraculously occurred on Earth to sustain life or science as we know it.
Ours is a very average position in the comic landscape and there is ample scope that very similar conditions are prevailing at other locations too. For example, in a classroom, many students will be found with marks near the average and very few far away from it.
This, per se, is not related to the idea of the multiverse but one can stretch the argument to microscopic configurations to ask if the occurrence of our universe is something special? Is our universe a miraculous entity or just an average one like many others? This is just stretching the initial argument.
Can you explain what string theory is? Does it explain the existence of a parallel universe?
String theory is a theoretical framework. It was initially envisioned to unite all the known forces of nature into one, in terms of a new fundamental entity — the strings.
Such unification requires that there ought to be more than four dimensions (the three spatial and the one-time dimension) we perceive, which is just the low energy manifestation of the grand picture.
Imagine it in this way — if you see a mural from close quarters, you will see only a small part of it. To see the full picture, you have to zoom out, but “zooming out” in case of a string theory needs extremely high energy.
Interesting, in many aspects, this leads to the question: Can we have different realisations of different 3+1 dimensions at low energy?
Carrying forwards the painting analogy, if you start coming close to the canvas, what is the guarantee that you will end up focussing on the same spot every time? There is always the likelihood of ending up on a different part of the painting the next time.
Similarly, you may end up getting a different 3+1 dimensional space in each low-energy migration. If so, can many co-exist? Do they constitute a multiverse? Many think that this is a possibility.
Many famous scientists like Leonard Susskind, Andrei Linde seemingly vouch for the existence of multiverse.
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