by Kristin Houser
The Nature of
Space and Time
A pair of researchers have uncovered a potential bridge between
general relativity and quantum mechanics - the two preeminent
physics theories - and it could force physicists to rethink the very
nature of space and time.
Albert Einstein's theory of general relativity describes
gravity as a geometric property of space and time. The more massive
an object, the greater its distortion of space-time, and that
distortion is felt as gravity.
In the 1970s,
physicists Stephen Hawking and Jacob Bekenstein
noted a link between the surface
area of black holes and their microscopic quantum structure, which
determines their entropy.
This marked the
first realization that a connection existed between Einstein's
theory of general relativity and quantum mechanics.
Less than three
decades later, theoretical physicist Juan Maldacena observed
link between between gravity and the quantum
world. That connection led to the creation of a model
that proposes that space-time can be created or destroyed by
changing the amount of entanglement between different surface
regions of an object.
In other words,
this implies that space-time itself, at least as it is defined in
models, is a product of the entanglement between objects.
To further explore
this line of thinking, Chun Jun Cao and Sean Carroll
of the California Institute of Technology (CalTech) set
out to see if they could actually derive the dynamical properties of
gravity (as familiar from general relativity) using the framework in
which space-time arises out of quantum entanglement.
Their research (Bulk
Entanglement Gravity without a Boundary - Towards finding Einstein's
Equation in Hilbert Space) was recently published in
Using an abstract
mathematical concept called
Hilbert space, Cao and Carroll were
able to find similarities between the equations that govern quantum
entanglement and Einstein's equations of general relativity.
This supports the
idea that space-time and gravity do emerge from entanglement.
Carroll told us the
next step in the research is to determine the accuracy of the
assumptions they made for this study.
"One of the
most obvious ones is to check whether the symmetries of
relativity are recovered in this framework, in particular, the
idea that the laws of physics don't depend on how fast you are
moving through space," he said.
A Theory of Everything
everything we know about the physical aspects of our universe can be
explained by either general relativity or quantum mechanics.
The former does a
great job of explaining activity on very large scales, such as
planets or galaxies, while the latter helps us understand the very
small, such as atoms and sub-atomic particles.
However, the two
theories are seemingly not compatible with one another.
This has led
physicists in pursuit of the elusive "theory
of everything" - a single framework that would explain it
all, including the nature of space and time.
Because gravity and
space-time are an important part of "everything," Carroll said he
believes the research he and Cao performed could advance the pursuit
of a theory that reconciles general relativity and quantum
Still, he noted
that the duo's paper is speculative and limited in scope.
doesn't say much, as yet, about the other forces of nature, so
we're still quite far from fitting ‘everything' together," he
Still, if we could
find such a theory, it could help us answer some of the biggest
questions facing scientists today.
We may be able to
finally understand the true nature of,
other mysterious cosmic objects.
researchers are tapping into the ability of the quantum
world to radically improve our
computing systems, and a
theory of everything could potentially speed up the process
by revealing new insights into the still largely confusing
theoretical physicists' progress in pursuit of a theory of
everything has been "spotty," according to Carroll, each new
bit of research - speculative or not - leads us one step
closer to uncovering it and ushering in a whole new era in
humanity's understanding of the universe.