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Universe' may collapse new studies predict

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  • blackstar7us
    Runaway universe may collapse in 10 billion years, new studies predict The recent discovery that the universe is expanding at an ever- increasing rate has
    Message 1 of 1 , Sep 18, 2002
      'Runaway universe' may collapse in 10 billion years, new studies
      The recent discovery that the universe is expanding at an ever-
      increasing rate has led many astronomers to forecast a dark and
      lonely future for our galaxy. According to some predictions, the
      rapidly accelerating universe will cause all galaxies to run away
      from each other until they are no longer visible. In this widely
      accepted scenario, our own Milky Way will become an isolated island
      adrift in a sea of totally black space 150 billion years from now.
      But two new studies by Stanford University cosmologists suggest that
      it may be time to rethink this popular view of a "runaway universe."
      Instead of expanding exponentially, our cosmos may be in danger of
      collapsing in a "mere" 10 to 20 billion years, according to the
      Stanford team.

      "The standard vision at the moment is that the universe is speeding
      up," said physics Professor Andrei Linde, "so we were surprised to
      find that a collapse could happen within such a short amount of time."

      Linde and his wife, Renata Kallosh – also a professor of physics at
      Stanford – have authored two companion studies that raise the
      possibility of a cosmic "big crunch." Both papers are available on
      the physics research website, www.arXiv.org. "We tried our best to
      come up with a good theory that explains the acceleration of the
      universe, but ours is just a model," Linde noted. "It's just part of
      the answer."

      If the Linde-Kallosh model is correct, then the universe, which
      appears to accelerating now, will begin to slow down and
      contract. "The universe may be doomed to collapse and disappear,"
      Linde said. "Everything we see now, and at a much larger distance
      that we cannot see, will collapse into a point smaller than a proton.
      Locally, it will be the same as if you were inside a black hole. You
      will just discontinue your existence."

      Einstein's "blunder"

      The fate of the cosmos has been hotly debated for decades.

      In the early 20th century, Albert Einstein, along with most
      physicists, believed that the universe was static – even though the
      equations he developed for his general theory of relativity in 1917
      suggested that space itself was either contracting or expanding. To
      ensure that his new theory was consistent with nature, Einstein
      invented the "cosmological constant": an arbitrary mathematical term
      he inserted into his equations to guarantee a static universe – at
      least on paper.

      To Einstein, the cosmological constant may have represented some kind
      of invisible energy that exists in the vacuum of empty space – a
      force strong enough to repel the gravitational force exerted by
      matter. Without this mysterious vacuum energy opposing gravity, the
      universe eventually would crash in on itself, according to general
      relativity theory.

      But observations by astronomer Edwin Hubble and others in the 1920s
      proved that distant galaxies are not stationary but are, in fact,
      moving away from one another. Since the universe was expanding,
      Einstein no longer needed an antigravity factor in his equations, so
      he rejected the cosmological constant as irrelevant.

      "First Einstein introduced the cosmological constant in his
      equations, then he said that this was the biggest blunder of his
      life," Linde observed. "But I recently heard that, apparently, he
      still liked the idea and discussed it many years later – and
      continued writing equations that included it."

      Dark energy

      Fast-forward to 1998, when two independent teams of astronomers
      discovered that not only is the universe expanding, it is doing so at
      an ever-faster pace. Their findings were based on observations of
      supernovae – exploding stars that emit extraordinarily bright light.
      A supernova is a rare event, but new telescopes equipped with
      sophisticated electronic sensors allowed the research teams to track
      dozens of stellar explosions in the sky. What they saw astonished the
      world of astronomy: The supernovae, it turned out, actually were
      speeding up at a rate that outpaced the predicted gravitational pull
      of matter.

      What force could be strong enough to overcome gravity and cause the
      universe to accelerate? Perhaps Einstein was right all along – maybe
      there is some kind of vacuum energy in space. Einstein called it the
      cosmological constant, and 80 years later, astronomers would give
      this invisible force a new name – dark energy.

      "The supernova experiments four years ago confirmed a simple picture
      of the universe where approximately 30 percent of it is made of
      matter and 70 percent is made of dark energy – whatever it is," Linde

      Overnight, a concept that Einstein had rejected was now considered
      the dominant force in the universe. "The cosmological constant
      remains one of the biggest mysteries of modern physics," Linde
      pointed out.

      Negative energy

      Current predictions that dark energy will continue to overwhelm
      gravity and produce a runaway universe are based on the assumption
      that the total density of dark energy in the universe is greater than
      zero and will remain so forever.

      This seems obvious at first glance, since logic dictates that the
      density of dark energy has to be a positive number. After all, how
      could the universe be filled with "negative energy"?

      But in the strange world of quantum physics and elementary particle
      theory, everyday logic doesn't always apply.

      "During the last year, physicists came to the realization that it is
      very difficult to understand the origin of positive dark energy in
      the most advanced versions of elementary particle theory – such as
      string theory and extended supergravity," Linde said.

      "We have found that some of the best attempts to describe dark energy
      predict that it will gradually become negative, which will cause the
      universe to become unstable, then collapse," he added. "People who
      studied general relativity many years ago were aware of this, but to
      them, this was an academic possibility. It was weird to think about
      negative vacuum energy seriously. Now we have some reasons to believe

      The Linde-Kallosh model produced another surprising result: The
      cosmos will collapse in 10 to 20 billion years – a timeframe
      comparable with the age of the universe, which is estimated to be
      about 14 billion years old.

      "This was really strange," Linde recalled. "Physicists have known
      that dark energy could become negative and the universe could
      collapse sometime in the very distant future, perhaps in a trillion
      years, but now we see that we might be, not in the beginning, but in
      the middle of the life cycle of our universe."

      The good news, wrote Linde and Kallosh, is that "we still have a lot
      of time to find out whether this is going to happen."

      Cosmic bubbles

      Linde is quick to acknowledge that the collapsing universe scenario
      is not the final word on the fate of the cosmos.

      "Astronomy is a science once known for its continuous errors," he
      quipped."There was even a joke: 'Astrophysicists are always in error
      but never in doubt.' We are just in the very beginning of our
      investigation of this issue, and it would be incorrect to interpret
      our results as a reliable doomsday prediction. In any case, our model
      teaches us an interesting lesson: Even the most abstract theories of
      elementary particles may end up having great importance in helping us
      understand the fate of the universe and the fate of humanity."

      Direct observation of space with state-of-the-art telescopes,
      satellites and other instruments will answer many unresolved
      questions, he added. "We're entering the era of precision cosmology,
      where we really can get a lot of data, and these data become more
      precise. Perhaps 10 years, 20 years, 30 years, I don't know, but this
      is the timescale in which we will get a map of the universe with all
      its observable parts. So things that were a matter of speculation
      will gradually become better and better established."

      Linde helped pioneer inflationary cosmology – the theory that the
      universe began not with a fiery big bang but with an extraordinarily
      rapid expansion (inflation) of space in a vacuum-like state.
      According to inflationary theory, what we call the universe is just a
      minute fraction of a much larger cosmos.

      "The universe actually looks, not like a bubble, but like a bubble
      producing new bubbles," Linde explained. "We live in a tiny part of
      one bubble, and we look around and say, 'This is our universe.'"

      If our bubble collapses into a point, a new bubble is likely to
      inflate somewhere else – possibly giving rise to an entirely new form
      of life, Linde said.

      "Our part of the universe may die, but the universe as a whole, in a
      sense, is immortal – it just changes its properties," he
      concluded. "People want to understand their place in the universe,
      how it was created and how it all will end – if at all. That is
      something that I would be happy to know the answer to and would pay
      my taxpayer money for. After all, it was never easy to look into the
      future, but it is possible to do so, and we should not miss our

      Graduate student Sergey Prokushkin and Marina Shmakova, a research
      associate at the Stanford Linear Accelerator Center, also contributed
      to the studies. Research was supported with grants from the National
      Science Foundation, the Templeton Foundation, the U.S. Department of
      Energy and the Stanford Graduate Fellowships program.
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