-
You don't exist in an infinite number ofplaces, say scientists25
January 2013, by Lisa Zyga
Infinite repetition, the idea that planets and living beingsmust
be repeated an infinite number of times, cannot belogically deduced
from current physics and cosmologytheories. Credit: NASA/Apollo
17
(Phys.org)If you've read about how moderncosmology may imply
that, in an infinite universe,the existence of planets and the life
forms that liveon them must be repeated an infinite number oftimes,
you may have been just a little bit skeptical.So are a couple
scientists from Spain, who haveposted a paper at arXiv.org
criticizing the conceptof the infinite repetition of histories in
space, anidea closely related to the concepts of
"alternatehistories," "parallel universes," and the "manyworlds
interpretation," among others.
Francisco Jos Soler Gil at the University of Sevillaand Manuel
Alfonseca at the AutonomousUniversity of Madrid have looked at two
differentproposals one based on classical cosmology andthe other on
quantum mechanics that contendthat we live in an infinite universe
in which historyis repeated an infinite number of times in
space.They have picked apart both proposals and arguethat both are
highly speculative, despite oftenbeing presented as plausible
ideas. Moreover, theyargue that we really don't know whether we
live inan infinite universe, as a finite one seems
equallylikely.
The basic idea of the infinite repetition of historiesin space
is that, if you take yourself right now andchange one thing (say
make your red shirt a blueone), then there's another you somewhere
who isexactly the same except for that one difference.Change your
shirt to purple, and that's a third you.
Change the drink in your hand from soda to tea, andthere's
another one. Plus, there are copies of all ofthese universes an
infinite number of copies. Intheir paper, Soler Gil and Alfonseca
quote thepopular science book "The Music of the Big Bang,The Cosmic
Microwave Background, and the NewCosmology" by Amedeo Balbi: "In an
infiniteuniverse, every possible event does happen. Notjust that:
it happens an infinite number of times."
This infinite repetition idea can be found in earlyphilosophy,
ancient mythology, and today's sci-filiterature. But can it be
derived from physicaltheories about the universe, and does it have
aplace in science?
In the first proposal that Soler Gil and Alfonsecaanalyze, Ellis
and Brundrit argue that infiniterepetition logically arises from
classic relativisticphysics. A more detailed summary can be found
inthe arXiv paper, but the general argument is asfollows. If the
universe, the number of planets andgalaxies, and the number of
possible histories (theone we're familiar with is our
13.7-billion-yearhistory) are all infinite; and if the probability
of DNA-based life is greater than zero; and if the number oftypes
of DNA-based living things is finite (becausethe size of the DNA
molecules cannot be arbitrarilylarge); then an infinite universe
must contain aninfinite number of copies of the finite number
ofDNA-based living things, and some of these livingthings will
follow very similar and even identicalhistory lines. In other
words, infinite histories plusfinite types of living things means
that those livingthings' histories are infinitely repeated.
Soler Gil and Alfonseca take issue with several ofthese
assumptions. One of their maincounterarguments at first seems odd:
they say thatwe can't be sure that the probability of DNA-basedlife
is greater than zero. Neither our existence nor
1 / 3
-
our discovery of a finite number of cases of life onother
planets can, at least in the logical sense, beused to deduce that
the probability is greater thanzero. As a result, the infinity of
histories is largerthan the infinity of living individuals, so each
planetcompatible with life could have its own uniquehistory.
"If there is an infinite number of possible histories,the fact
that there is a given history (or a finitenumber) leading to life
does not make that historyprobable: its probability would be 1
divided byinfinity, which is zero," Alfonseca explained to
Phys.org. "To have a greater-than-zero probability,you need an
infinite number of approaches. But inany case, with this scenario,
the number ofhistories would always be larger than the number
ofbeings, so the same beings infinitely repeatedwould still have
different histories."
The second proposal, by Garriga and Vilenkin,does involve a
finite number of histories, but isrooted on the idea in quantum
theory that discreteregions of space have finite amounts of energy.
Inthe decoherent histories (DH) interpretation ofquantum mechanics,
the infinite universe can bedivided into an infinite number of
regions thatcannot influence one another (i.e., they're
causallydisconnected) because they are separated byevent horizons.
Then Garriga and Vilenkin deducethat the number of possible
histories in each regionis finite because the energy in each region
is finiteand, according to quantum mechanics, energy isquantified.
To put it briefly, an infinite number ofregions plus a finite
number of possible histories ineach region means that every history
must berepeated an infinite number of times.
Soler Gil and Alfonseca criticize almost all of theassumptions
in this proposal, starting with theapplication of quantum theory to
cosmology, whichis currently mere conjecture without evidence.Other
problems arise when considering thegravitational effects of black
holes and theexpansion of the universe, which can
potentiallyincrease the number of possible historiesindefinitely,
preventing repetitions.
But the scientists' biggest criticism of the idea ofinfinite
repetition in both proposals is theassumption that the universe is
infinite. Whetherthe universe is infinite or finite is a big
open-endedquestion in cosmology that scientists may neveranswer.
Soler Gil and Alfonseca note that, lookingback at the history of
physics, situations emergedwhere infinities seemed impossible to
avoid, yetimproved theories eliminated the infinities.Currently the
two basic theories in physics, generalrelativity and quantum
theory, both predict infinities.In relativity, it's gravity
singularities in black holesand the big bang. In quantum theory,
it's vacuumenergy and certain parts of quantum field theory.Perhaps
both theories are simple approximations ofa third more general
theory without infinities. SolerGil and Alfonseca also note that,
Paul Dirac oncestated that the most important challenge in
physicswas "to get rid of infinity."
While Soler Gil and Alfonseca can't disprove theproposals of
infinite repetition, they emphasize thatthe point of their critique
is to show that the idearemains in the realm of philosophy,
mythology, andsci-fi tales, not modern cosmology. They call
thespeculation "ironic science," a term used byscience journalist
John Horgan to describe optionsthat do not converge on truth but
are at best"interesting." Despite the accounts of many
popularscience books, the idea that our lives are beingrepeated an
infinite number of times somewhereout in the universe is in no way
certain and far fromeither probable or plausible.
More information: Francisco Jos Soler Gil andManuel Alfonseca.
"About the Infinite Repetition ofHistories in Space."
arXiv:1301.5295 [physics.hist-ph]
2013 Phys.org
2 / 3
-
APA citation: You don't exist in an infinite number of places,
say scientists (2013, January 25) retrieved 19March 2015 from
http://phys.org/news/2013-01-dont-infinite-scientists.html
This document is subject to copyright. Apart from any fair
dealing for the purpose of private study or research, no partmay be
reproduced without the written permission. The content is provided
for information purposes only.
Powered by TCPDF (www.tcpdf.org)
3 / 3
