Önce Quora.com'dan aldığım bir metni ve onun çevirisini aldım aşağıya; ardından da bu metne dair claude'un değerlendirmesi ekledim. Meraklısı kaçırmasın derim.
Roger Penrose says, "String theory is fashion, quantum physics is
faith, and cosmic inflation is fantasy." Is he right?
To call Penrose a mathematician,
using a derisory tone, is a gross misrepresentation of Penrose’s areas of
expertise. The correct characterisation is that Penrose is one of the few
mathematical physicists who really understands General Relativity and has very
credible criticisms of mostly US trained particle physicists who moved into
unification and cosmology with only an undergraduate knowledge of GR. GR is far
more than just a theory of gravitation, its contains deep truths about what we
mean by location, and duration, and about the non-existence of coordinate
location. It is false to point at a point in space and give it any meaningful
existence. The only thing meaningful is the location of fields and matter in
relation to each other and in particular in relation to the gravitational
field. Those who think that GR describes a space with a metric which determines
distance and duration are very mistaken. The entire diffeomorphic symmetry of
GR dictates that under all general coordinate transformations, the underlying
structure is invariant. This is what makes location so slippery, because its
only real matter (energy-momentum) in relation to the gravitational field
(curvature) which specifies a co-location.
The particle physicists neglect the
important contribution of the gravitational degrees of freedom, and they way
they dominate over matter in the early universe. Inventing inflation to ensure
that the matter and temperature are uniform, is wagging the dog. If the
gravitational modes were active before inflation, the result would be a
non-uniform mess. Penrose, as usual, points out that the fundamental problem is
the extremely low entropy of the initial big bang state, which is responsible
not only for the homogeneity of the cosmos, but the very arrow of time,
generating all the complexity we now see after 13.6 billion years. He points
out that for this to be true, right at the Big Bang, a quantity called the Weyl
Tensor, (responsible for bending of starlight during an eclipse), must have
been exactly zero, meaning the gravitational field was perfectly uniform. Since
all matter fields are created out of the vacuum, this condition is necessary
for inflation to produce a uniform state, it does not in itself solve the
problem. The inflation proponents just look at this and scratch their heads,
what do particle physicists understand about General Relativity?
I am getting tired of pointing out
that String Theory arose out of particle physicists attempting to quantise the
linearised version of GR, normally used in make perturbations to Newton’s laws
in the solar system. This produces a free spin-2 graviton at 0th-level, and
then they attempt to use first order interactions to construct a full
interacting quantum field theory of gravitons - in FLAT space - which has none
of the full symmetries of GR, and it fails miserably by throwing up infinities
at all orders. Not to be daunted, they added supersymmetry to cancel the
infinities, but that did not work as expected, so they invented Strings instead
of points, to remove the short distance interactions. Why would this ad-hoc
procedure produce anything like Quantum GR? It gets worse, they quantise this
strings in FLAT spacetime, but find that they need 10 dimensions instead of 4,
so they then ‘compactify’ 6 to get something like our world. Problem is, there
is about 10^500 different ways to do this - hence the multiverse. Never before
has such a failed theory taken on such a life of its own, at least the
Aristotelian epicycles produced decent predictions.
As it turns out, when a group of
physicists including Lee Smolin and Carlo Rovelli, who understood GR, actually
found a way to quantise the arbitrary curved spacetime of GR directly,
respecting its symmetries, what dropped out was a real theory of quantum
gravity, with no extra dimensions, no supersymmetry, no 10^500 different
universes, just a set of quantum states of space, based on simple geometrical
solids connected like Lego, each with unique quantum numbers, which at the
large scale looks like the space-time of General Relativity. This theory is
Loop Quantum Gravity. It turns out that the mathematical structure of these
quantum states, had been found two decades earlier by Penrose, while looking
for possible quantum states of gravity. Like String Theory, LQG is not yet
experimentally verifiable either, but it has been used to specify exact states
of a black-hole horizon, and in the early universe to avoid an initial
singularity. It does what a quantum theory of gravity, which respects GR, would
be expected to do. There is much to do, but GR has always been very hard to
find and understand its solutions, and any quantum version would be equally
difficult. There are proposals for experiments to look at light from distant
galaxies, for any sign of the granularity of space, accumulated over billions
of years, which may just be detectable in the near future.
Penrose’s views on Quantum Theory are speculative, but
there are many different interpretations, and at least he makes proposals which
can be experimentally falsified. He speculates on dimensional grounds, that the
Planck Mass, usually associated with a quantum black hole, when turned into
everyday units, is about 2 x 10–5 grams, which is tantalisingly close to the
scale above which quantum properties are not observed. He conjectures that the
gravitational disturbance caused by the movement of this mass, is responsible
for the “collapse of the wavefunction” which occurs during quantum measurement
on a macroscopic system. Perhaps more controversial, he suggests that there may
be processes in the human brain at this scale, which may allow quantum
mechanical effects to be related to consciousness. He enlisted a medical
researcher Stuart Hameroff to assist his development of these ideas. But none
of this is anything other than scientific enquiry, ultimately decidable by
experimental data.
*** Çeviri
Roger Penrose şöyle diyor: "String teorisi
bir moda, kuantum fiziği bir inanç, kozmik enflasyon ise bir fantezidir."
Haklı mı?
Penrose'u küçümseyici bir tonla "sadece bir
matematikçi" olarak nitelemek, onun uzmanlık alanını ciddi şekilde
çarpıtmaktır. Doğru tanım şudur: Penrose, Genel Görelilik'i (GR) gerçekten
anlayan ender matematiksel fizikçilerden biridir ve çoğunlukla ABD'de eğitim
görmüş, GR konusunda yalnızca lisans düzeyinde bilgiyle birleştirme
(unification) ve kozmolojiye yönelmiş parçacık fizikçilerine yönelik son derece
güvenilir eleştiriler getirmektedir. GR yalnızca bir yerçekimi teorisi
değildir; konum ve süre ile ne kastettiğimize, koordinat-konumun var olmayışına
dair derin gerçekler içerir. Uzayda bir noktayı işaret edip ona anlamlı bir
varlık atfetmek yanlıştır. Anlamlı olan tek şey, alanların ve maddenin
birbirlerine göre, özellikle de yerçekimi alanına göre konumudur. GR'nin,
mesafeyi ve süreyi belirleyen bir metriğe sahip bir uzayı tanımladığını
düşünenler büyük yanılgı içindedir. GR'nin bütünüyle diffeomorfik simetrisi,
tüm genel koordinat dönüşümleri altında temel yapının değişmez kaldığını
buyurur. Konumun bu kadar "kaypak" olmasının sebebi budur; çünkü
gerçekte var olan yalnızca enerji-momentumun yerçekimi alanına (eğriliğe) göre
konumudur ve bu da bir "ortak-konumlanma" belirler.
Parçacık fizikçileri, yerçekimsel serbestlik
derecelerinin önemini ve bunların erken evrende maddeye baskın gelme biçimini
göz ardı etmektedir. Madde ve sıcaklığın homojen olmasını sağlamak için
enflasyonu icat etmek, "kuyruğun köpeği sallaması" gibidir. Eğer
enflasyondan önce yerçekimsel modlar aktif olsaydı, sonuç homojen olmayan bir
karmaşa olurdu. Penrose her zamanki gibi, temel sorunun Big Bang'in başlangıç
durumundaki son derece düşük entropi olduğuna işaret eder; bu düşük entropi yalnızca
kozmosun homojenliğinden değil, aynı zamanda 13,6 milyar yıl sonra gördüğümüz
tüm karmaşıklığı üreten zamanın okundan da sorumludur. Bunun doğru olabilmesi
için, Big Bang anında, Weyl Tensörü adı verilen ve (bir tutulma sırasında
yıldız ışığının bükülmesinden sorumlu) niceliğin tam olarak sıfır olması
gerektiğini belirtir; bu da yerçekimi alanının mükemmel derecede homojen olduğu
anlamına gelir. Tüm madde alanları vakumdan yaratıldığından, bu koşul
enflasyonun homojen bir durum üretebilmesi için gereklidir, ancak sorunu kendi
başına çözmez. Enflasyon savunucuları buna bakıp şaşkınlıkla kafa kaşırlar;
parçacık fizikçileri Genel Görelilik hakkında ne anlıyor ki?
