Andrew Yee[_1_]
April 27th 07, 04:22 AM
Division of Public Affairs
Vanderbilt University
Nashville, Tennessee
Media Contact:
David F. Salisbury, (615) 343-6803
4-25-2007
Cosmologically speaking, diamonds may actually be forever
If you've ever wondered about the ultimate fate of the universe, Lawrence
Krauss and Robert Scherrer have some good news ... sort of.
Writing in the journal Physical Review D, the two physicists show that
matter as we know it will remain as the universe expands at an
ever-increasing clip. That is, the current status quo between matter and its
alter ego, radiation, will continue as the newly discovered force of dark
energy pushes the universe apart.
"Diamonds may actually be forever," quips Krauss, professor of physics and
astronomy at Case Western Reserve University (CWRU) who is spending the year
at Vanderbilt. "One of the only positive things that has arisen from the
dark-energy dominated universe is that matter gets to beat radiation
forever!"
Although this may not sound surprising, it actually runs contrary to
conventional wisdom among cosmologists. Today, there is more matter than
radiation in the universe. But there were periods during the early universe
that were dominated by radiation due to particle decays. The generally
accepted view of the distant future has been that ordinary matter particles
-- protons and neutrons in particular -- will gradually decay into radiation
over trillions upon trillions of years, leaving a universe in which
radiation once again dominates over matter; a universe lacking the material
structures that are necessary for life.
It is only in the last decade that the existence of dark energy has been
recognized. Before that Krauss and collaborators argued for its existence
based on indirect evidence, but the first direct evidence came in 1998 when
a major survey of exploding stars, called supernovae, revealed that the
universe is apparently expanding at an increasing rate. Dark energy acts as
a kind of anti-gravity that drives the expansion of the universe at large
scales. Because it is associated with space itself, it is also called
"vacuum energy." A number of follow-up observations have supported the
conclusion that dark energy accounts for about 70 percent of all the energy
in the universe.
"The discovery of dark energy has changed everything, but it has changed the
view of the future more than the past. It is among the worst of all possible
futures for life," says Krauss, who has spent the last few years exploring
its implications. In an eternally expanding universe there is at least a
chance that life could endure forever, but not in a universe dominated by
vacuum energy, Krauss and CWRU collaborator Glenn Starkman have concluded.
As the universe expands, the most distant objects recede at the highest
velocity. The faster that objects recede, the more that the light coming
from them is "red-shifted" to longer wavelengths. When their recessional
velocity reaches light speed, they disappear because they are traveling away
faster than the light that they emit. According to Krauss and Starkman, the
process of disappearance has already begun: There are objects that were
visible when the universe was half its present age that are invisible now.
However, the process won't become really noticeable until the universe is
about 100 billion years old. By ten trillion years, nothing but our local
cluster of galaxies will be visible.
From the perspective of future civilizations, this process puts a finite
limit on the amount of information and energy that will be available to
maintain life. Assuming that consciousness is a physical phenomenon, this
implies that life itself cannot be eternal, Krauss and Starkman argue.
"Our current study doesn't change the process, but it does make it a little
friendlier for matter and less friendly for radiation," says Scherrer,
professor of physics at Vanderbilt.
In their paper, Krauss and Scherrer analyzed all the ways that ordinary
matter and dark matter could decay into radiation. (Dark matter is different
from dark energy. It is an unknown form of matter that astronomers have only
been able to detect by its gravitational effect on the ordinary matter in
nearby galaxies. At this point, the physicists have no idea whether it is
stable or will ultimately decay like ordinary matter.) Given known
constraints on these various decay processes, the two show that none of them
can produce radiation densities that exceed the density of the remaining
matter. This is counter-intuitive because, when matter turns into energy, it
does so according to Einstein's equation, E=mc2, and produces copious
amounts of energy.
"The surprising thing is that radiation disappears as fast as it is created
in a universe with dark energy," says Krauss.
The reason for radiation's vanishing act involves the expansion of space.
Expanding space diminishes the density of radiant energy in two ways. The
first is by increasing the separation between individual photons. The second
is by reducing the amount of energy carried by individual photons. A
photon's energy is contained entirely in its electromagnetic field. The
shorter its wavelength and the higher its frequency, the more energy it
contains. As space itself expands, the wavelengths of all the photons within
it lengthen and their frequency drops. This means that the amount energy
that individual photons contain also decreases. Taken together, these two
effects dramatically reduce the energy density of radiation.
Protons and neutrons, by contrast, only suffer from the separation effect.
Most of the energy that they carry is bound up in their mass and is not
affected by spatial expansion. In an accelerating universe, that is enough
of an advantage to maintain matter's dominance ... forever.
NOTE: A multimedia version of this story is available on Exploration,
Vanderbilt's online research magazine, at
http://www.vanderbilt.edu/exploration/stories/matterdom.html
Vanderbilt University
Nashville, Tennessee
Media Contact:
David F. Salisbury, (615) 343-6803
4-25-2007
Cosmologically speaking, diamonds may actually be forever
If you've ever wondered about the ultimate fate of the universe, Lawrence
Krauss and Robert Scherrer have some good news ... sort of.
Writing in the journal Physical Review D, the two physicists show that
matter as we know it will remain as the universe expands at an
ever-increasing clip. That is, the current status quo between matter and its
alter ego, radiation, will continue as the newly discovered force of dark
energy pushes the universe apart.
"Diamonds may actually be forever," quips Krauss, professor of physics and
astronomy at Case Western Reserve University (CWRU) who is spending the year
at Vanderbilt. "One of the only positive things that has arisen from the
dark-energy dominated universe is that matter gets to beat radiation
forever!"
Although this may not sound surprising, it actually runs contrary to
conventional wisdom among cosmologists. Today, there is more matter than
radiation in the universe. But there were periods during the early universe
that were dominated by radiation due to particle decays. The generally
accepted view of the distant future has been that ordinary matter particles
-- protons and neutrons in particular -- will gradually decay into radiation
over trillions upon trillions of years, leaving a universe in which
radiation once again dominates over matter; a universe lacking the material
structures that are necessary for life.
It is only in the last decade that the existence of dark energy has been
recognized. Before that Krauss and collaborators argued for its existence
based on indirect evidence, but the first direct evidence came in 1998 when
a major survey of exploding stars, called supernovae, revealed that the
universe is apparently expanding at an increasing rate. Dark energy acts as
a kind of anti-gravity that drives the expansion of the universe at large
scales. Because it is associated with space itself, it is also called
"vacuum energy." A number of follow-up observations have supported the
conclusion that dark energy accounts for about 70 percent of all the energy
in the universe.
"The discovery of dark energy has changed everything, but it has changed the
view of the future more than the past. It is among the worst of all possible
futures for life," says Krauss, who has spent the last few years exploring
its implications. In an eternally expanding universe there is at least a
chance that life could endure forever, but not in a universe dominated by
vacuum energy, Krauss and CWRU collaborator Glenn Starkman have concluded.
As the universe expands, the most distant objects recede at the highest
velocity. The faster that objects recede, the more that the light coming
from them is "red-shifted" to longer wavelengths. When their recessional
velocity reaches light speed, they disappear because they are traveling away
faster than the light that they emit. According to Krauss and Starkman, the
process of disappearance has already begun: There are objects that were
visible when the universe was half its present age that are invisible now.
However, the process won't become really noticeable until the universe is
about 100 billion years old. By ten trillion years, nothing but our local
cluster of galaxies will be visible.
From the perspective of future civilizations, this process puts a finite
limit on the amount of information and energy that will be available to
maintain life. Assuming that consciousness is a physical phenomenon, this
implies that life itself cannot be eternal, Krauss and Starkman argue.
"Our current study doesn't change the process, but it does make it a little
friendlier for matter and less friendly for radiation," says Scherrer,
professor of physics at Vanderbilt.
In their paper, Krauss and Scherrer analyzed all the ways that ordinary
matter and dark matter could decay into radiation. (Dark matter is different
from dark energy. It is an unknown form of matter that astronomers have only
been able to detect by its gravitational effect on the ordinary matter in
nearby galaxies. At this point, the physicists have no idea whether it is
stable or will ultimately decay like ordinary matter.) Given known
constraints on these various decay processes, the two show that none of them
can produce radiation densities that exceed the density of the remaining
matter. This is counter-intuitive because, when matter turns into energy, it
does so according to Einstein's equation, E=mc2, and produces copious
amounts of energy.
"The surprising thing is that radiation disappears as fast as it is created
in a universe with dark energy," says Krauss.
The reason for radiation's vanishing act involves the expansion of space.
Expanding space diminishes the density of radiant energy in two ways. The
first is by increasing the separation between individual photons. The second
is by reducing the amount of energy carried by individual photons. A
photon's energy is contained entirely in its electromagnetic field. The
shorter its wavelength and the higher its frequency, the more energy it
contains. As space itself expands, the wavelengths of all the photons within
it lengthen and their frequency drops. This means that the amount energy
that individual photons contain also decreases. Taken together, these two
effects dramatically reduce the energy density of radiation.
Protons and neutrons, by contrast, only suffer from the separation effect.
Most of the energy that they carry is bound up in their mass and is not
affected by spatial expansion. In an accelerating universe, that is enough
of an advantage to maintain matter's dominance ... forever.
NOTE: A multimedia version of this story is available on Exploration,
Vanderbilt's online research magazine, at
http://www.vanderbilt.edu/exploration/stories/matterdom.html