At
first glance, there is not the slightest doubt: to us, the universe looks three
dimensional. But one of the most fruitful theories of theoretical physics in
the last two decades is challenging this assumption. The "holographic
principle" asserts that a mathematical description of the universe
actually requires one fewer dimension than it seems. What we perceive as three
dimensional may just be the image of two dimensional processes on a huge cosmic
horizon.
Up
until now, this principle has only been studied in exotic spaces with negative
curvature. This is interesting from a theoretical point of view, but such
spaces are quite different from the space in our own universe. Results obtained
by scientists at TU Wien (Vienna) now suggest that the holographic principle
even holds in a flat spacetime.
The Holographic Principle
Everybody
knows holograms from credit cards or banknotes. They are two dimensional, but
to us they appear three dimensional. Our universe could behave quite similarly:
"In 1997, the physicist Juan Maldacena proposed the idea that there is a
correspondence between gravitational theories in curved anti-de-sitter spaces
on the one hand and quantum field theories in spaces with one fewer dimension
on the other," says Daniel Grumiller (TU Wien).
Gravitational
phenomena are described in a theory with three spatial dimensions, the
behaviour of quantum particles is calculated in a theory with just two spatial
dimensions -- and the results of both calculations can be mapped onto each
other. Such a correspondence is quite surprising. It is like finding out that
equations from an astronomy textbook can also be used to repair a CD-player.
But this method has proven to be very successful. More than ten thousand
scientific papers about Maldacena's "AdS-CFT-correspondence" have
been published to date.
Correspondence Even in Flat Spaces
For
theoretical physics, this is extremely important, but it does not seem to have
much to do with our own universe. Apparently, we do not live in such an
anti-de-sitter-space. These spaces have quite peculiar properties. They are
negatively curved, any object thrown away on a straight line will eventually
return. "Our universe, in contrast, is quite flat -- and on astronomic
distances, it has positive curvature," says Daniel Grumiller.
However,
Grumiller has suspected for quite some time that a correspondence principle
could also hold true for our real universe. To test this hypothesis,
gravitational theories have to be constructed, which do not require exotic
anti-de-sitter spaces, but live in a flat space. For three years, he and his
team at TU Wien (Vienna) have been working on that, in cooperation with the
University of Edinburgh, Harvard, IISER Pune, the MIT and the University of
Kyoto. Now Grumiller and colleagues from India and Japan have published an
article in the journal Physical Review Letters, confirming the validity
of the correspondence principle in a flat universe.
Calculated Twice, Same Result
"If
quantum gravity in a flat space allows for a holographic description by a
standard quantum theory, then there must be physical quantities, which can be
calculated in both theories -- and the results must agree," says
Grumiller. Especially one key feature of quantum mechanics -quantum
entanglement -- has to appear in the gravitational theory.
When
quantum particles are entangled, they cannot be described individually. They
form a single quantum object, even if they are located far apart. There is a
measure for the amount of entanglement in a quantum system, called
"entropy of entanglement." Together with Arjun Bagchi, Rudranil Basu
and Max Riegler, Daniel Grumiller managed to show that this entropy of
entanglement takes the same value in flat quantum gravity and in a low
dimension quantum field theory.
"This
calculation affirms our assumption that the holographic principle can also be
realized in flat spaces. It is evidence for the validity of this correspondence
in our universe," says Max Riegler (TU Wien). "The fact that we can
even talk about quantum information and entropy of entanglement in a theory of
gravity is astounding in itself, and would hardly have been imaginable only a
few years back. That we are now able to use this as a tool to test the validity
of the holographic principle, and that this test works out, is quite
remarkable," says Daniel Grumiller.
This
however, does not yet prove that we are indeed living in a hologram -- but
apparently there is growing evidence for the validity of the correspondence
principle in our own universe.
Affirm: doğrulamak,
onaylamak
Assert: iddia etmek
Astound:şaşırtmak
At first glance: ilk
bakışta
Challenging: iddialı
Correspondence: uygunluk
Curvature: eğrilik
Curved: kavisli
Doubt:şüphe(lenmek)
Entangle: karıştırmak,
başını derde sokma
Entropy: dağınım,
entropi, düzensizlik
Gravitational: yer
çekimiyle ilgili
Hold true: doğru kalmak,
doğru olmak
In cooperation with:
işbirliği ile
Peculiar: özel mülk,
tuhaf, hususi
Phenomenon: olay, olgu, olağanüstü
şey, fenomen
Remarkable: dikkate değer
Slight: az, hafif,
önemsiz
Throw away: kaçırmak,
boşa harcamak
Journal Reference:
1.
Arjun Bagchi, Rudranil Basu, Daniel Grumiller, Max
Riegler. Entanglement Entropy in Galilean Conformal Field Theories and Flat
Holography. Physical Review Letters, 2015; 114 (11) DOI: 10.1103/PhysRevLett.114.111602
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