Обнаружен квантовый гравитационный эффект

19:00 16 January 02
Hazel Muir
 
Gravity's subtle influence in the quantum world has been directly
observed for the first time.

On tiny scales, nature makes particles behave according to
curiously rigid rules. For instance, negatively charged electrons
trapped around a positive nucleus under the pull of the
electromagnetic force cannot have any energy they want -they
have to fall into a set of distinct energy levels.

In the same way, the pull of gravity should make particles fall
into discrete energy levels. But because gravity is extremely
weak on small scales, the effect has been impossible to spot.
"To be able to measure it, you need to suppress interference
from all the other fields," says Valery Nesvizhevsky of the
Laue-Langevin Institute in Grenoble, France.

Now Nesvizhevsky and his colleagues have achieved the feat
using a beam of neutrons. Neutrons were ideal because they're
neutral, so they don't feel the electromagnetic force and can
ignore its quantum rules.

Experts say it is a convincing result from an extremely tricky
experiment. "The difficulty of this measurement should not be
underestimated," says Thomas Bowles of Los Alamos National
Laboratory in New Mexico. "In the quantum realm, the
gravitational force is so weak that it is difficult to observe
quantum effects."


Bouncing neutrons

Nesvizhevsky's team took a beam of ultracold neutrons with tiny
energies, moving from left to right at less than eight metres per
second. Under the force of gravity, the neutrons fell down onto a
reflecting mirror and bounced off it before arriving at a detector.

The team could limit the energies of the neutrons arriving at the
detector by placing an absorbing material at different heights
above the mirror. The material mopped up all the neutrons that
bounced too high.

Forgetting quantum mechanics, you would expect neutrons with
any energy to arrive at the detector. But no neutrons appeared
unless the neutron-mop was at least 15 micrometres above the
mirror. This means the neutrons have to have a certain,
minimum energy (equal to 1.41 x 10-12 electronvolts) in the
Earth's gravitational field.


Step up

There were also hints that neutron transmission took little leaps
at different, higher energies, corresponding to higher quantum
levels. However, the team has still to confirm this.

Nesvizhevsky says the technology is exciting because it could
test some other key ideas in physics - for instance, whether or
not the neutron carries some minuscule amount of electric
charge. "If it's there, it's very, very small," says Nesvizhevsky.

It could also put on trial the equivalence principle, a famous
concept of Einstein's. It says that all particles, regardless of
their mass or composition, should fall with the same
acceleration in a uniform gravitational field.

Journal reference: Nature (vol 415, p 297)

Мне результат опыта кажется удивительным.

В ОТО сказано, что гравитация - это искривление пространства. Сейчас мне слабо найти решения уравнения Шредингера для пучка в слабо искривленном пространстве, но по наитию кажется, что спектр должен быть непрерывным. Волны будут "кривоватыми", а спектр непрерывным, поскольку движение неограниченное.

А тут дискретный спектр. Он может получиться из решения уравнения Шредингера в "прямом" пространстве с гравитационной энергией, включённой в потенциал.

То есть, получается, что гравитация - более обыкновенное поле, чем мы думали?

Конечно, всё это пока на уровне трёпа: надо действительно нарисовать два гамильтониана и найти собственнные значения. Будем надеяться, в ближайшие месяцы это сделают.

Аж жаль, что ушёл из физики

Спасибо за интересную статью.