A Critique of Hugh Everett's Multiverse
CMAP (Centre de Mathématiques APpliquées) UMR CNRS 7641, École polytechnique, Institut Polytechnique de Paris, CNRS, France
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[en français/in french]
Keywords: Multiverse, Multivers.
The state of a quantum system is described by its wave function,
whose time evolution is governed by the Schrödinger equation. This allows us to calculate the possible
outcomes {Ri} of a measurement on this system, as well as their probabilities {Pi} of occurrence.
During the act of measurement, only one result will appear among the set of possible outcomes {Ri}.
If the experiment is repeated, the different results {Ri} will appear according to the probabilities
{Pi}, as is verified daily with astonishing precision.
However, one of the great mysteries
of Quantum Mechanics is understanding what is known as the collapse of the wave function that
is, the selection of a single result among N possibilities. Is this an intrinsically random
process [01], or is there a hidden "mechanism" [02] that governs this selection?
In 1975,
Hugh Everett proposed a deterministic solution to this problem in his thesis: at each measurement,
the Universe "splits" into as many copies as there are possible outcomes.
This proposition has the
elegance of simplicity, even though it severely challenges Occam's razor...
At the same time, I find myself asking two questions about it, to which I do not know the answer, and which might challenge its validity:
- What happens to the probabilities {Pi}?
Indeed, in general,
not all measurement outcomes Ri have the same probability Pi of occurring. Yet, in Hugh Everett's
process, the splitting occurs unconditionally. How, then, can these probabilities be evaluated experimentally in this Multiverse?
- Is Special Relativity respected?
Since 1905 and Einstein's
Special Relativity, we know that the notion of simultaneity is relative. This means that for
two events, E1 and E2, in spacetime, depending on an observer's motion,
E1 and E2 may be perceived
as simultaneous (E1=E2),
or E1 may precede E2 (E1<E2),
or E1 may follow E2 (E1>E2).
In Hugh Everett's model, the events E correspond
to measurements M, and at each measurement, the Universe bifurcates by duplicating itself
into as many copies as necessary so that each branch of this tree structure corresponds to one of the
possible outcomes Ri. But if we consider not just one measurement but two, M1 and M2,
in what temporal order should the Universe split? Should the bifurcations occur
as M1 then M2 (M1<M2),
or M2 then M1 (M1>M2),
or in some other (a priori indeterminate) way when M1=M2?
Under these conditions, can these demultiplications have any physical meaning? Is Reality thus made?
If we naively add to this the idea that the Universe is "spatially and temporally" much, much vaster [03] than any
of our Physics laboratory, then these questions can only be further justified...
- [01]
Of course, we recall Einstein's famous "God does not play dice".
- [02]
Despite numerous experiments suggesting otherwise.
- [03]
Will still don't know whether it is finite or infinite...
Copyright © Jean-François COLONNA, 2025-2025.
Copyright © CMAP (Centre de Mathématiques APpliquées) UMR CNRS 7641 / École polytechnique, Institut Polytechnique de Paris, 2025-2025.
