One of the chief astrophysicists behind the discovery of the acceleration of the expansion of the universe, among the most startling revelations in the history of cosmology, delights in the confusion about the observation. In fact, he wonders if the acceleration will end up being the most important feature in the ultimate explanation. “It might be something unexpected that looks like acceleration,” says Saul Perlmutter, leader of the Supernova Cosmology Project (SCP), which first announced the astonishing fact in 1998. Ever the experimentalist, the 48-year-old Perlmutter is waiting, and planning, for more observations: “Until we go for a long run of more data, this just isn’t a mature field.”

Perlmutter philosophizes about the strangeness of the cosmos from his office at Lawrence Berkeley National Laboratory, high in the western hills of the San Francisco Bay Area. The room is the scientist’s amalgam of too many computer screens, too many piles of papers and an equation-filled whiteboard that would have done Einstein proud. The spectacular view of the Golden Gate Bridge in the distance cannot help but promote lofty thinking.

It has been a decade since the science community learned of the shocking discovery made by Perlmutter’s group and, independently, by the High-Z Supernova Search Team led by Brian Schmidt of the Australian National University (with analyses pioneered by Adam Riess of the Space Telescope Science Institute). The cosmos, the researchers found, is not just expanding; for unknown reasons, it is speeding up in its expansion.

The discovery took years of innovation and problem solving. The key was supernovae—specifically, those called type Ia. Such events are surprisingly invariable—the explosions have an intrinsic brightness that predictably fades over time, enabling astronomers to use them as “standard candles” and thus determine their distances from Earth. Perlmutter worked with Carl Pennypacker of the University of California, Berkeley, in the 1980s to robotically search for supernovae at relatively nearby distances. The field was then so young that their main competition came from Robert Evans, an amateur astronomer in Australia who identified supernovae with a backyard telescope.

In the beginning, the difficulty for Perlmutter’s group lay in obtaining telescope time, always precious in the astronomical community. How would the researchers convince allocators to give them the chance to look for something—a supernova explosion—that had not yet taken place? So they worked out methods to predict and automatically detect supernovae in a given patch of the sky. But their goal of determining the universe’s dynamics—then thought to be a decelerating expansion dominated by matter—still required additional observation to plot supernovae’s brightness peaks and declines, which take place over a few weeks. Perlmutter twisted arms and begged colleagues for an hour or two on short notice, calling frantically around the world at all times of the day. Everyone knew him, he says, as half-annoying. “I was always worried about something that had to happen in the next 24 hours or sometimes the next two hours. It was a terrible way to lead an ordinary life,” he recalls.

But persistence paid off. Observations of distant type Ia supernovae found them to be dimmer than expected. After eliminating the possibility of intergalactic dust and after years of painstaking data gathering and analysis at telescopes around the world (and in orbit), Perlmutter’s team came to the conclusion that, incredibly, the universe is not only expanding, as Edwin Hubble discovered in 1929, but that its expansion rate is increasing. Some unknown force with negative pressure seems to be pushing the universe apart.

Subsequent balloon-borne observations of the cosmic microwave background made two years later showed that the universe is spatially flat—it was stretched out by an exponential expansion, called inflation, right after the big bang. The equations behind these experiments complemented those of the supernova teams taken a few years earlier, and together the results enabled scientists to calculate separately the density of dark energy in the universe and the density of matter.

10 Comments

1. 1. Ian Timothy 09:11 PM 5/3/08

   While matter may not travel faster than the speed of light, is it not possible that if the speed of light at some time in the long-distant past -- before the Big Bang maybe -- was significantly greater than it is currently, it may then have been able to travel just fractionally faster than the speed of light is now?
   (Yes, I know that the prevailing wisdom has it that there is no such thing as "before" the Big Bang. There is also a school of thought advocating be proposition that there is a constant sequence of Big Bangs, separated from each other by a period of expansion and contraction -- which leads to the next one...)
   I know that's not regarded as remotely likely but, might it not allow that those objects at the furthest reaches of the universe as we perceive it now might not actually exist? If that fundamental proposition was valid, those objects might actually be images of galaxies etc. that were heading in this direction from most, if not all quarters, their journey culminating in the Big Bang. Because of the differing speeds of light, the whole pre-Big Bang process would be seen in reverse but because we are new developments on the planet, we haven't been able to observe the last 14 billion years of it! It also occurred to me that if that were the case, it would explain why everything at the far reaches of the universe appears to be leaving us at ever-increasing speed.
   
   You'll have to excuse me -- I'm no scientist, so feel free to laugh!

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2. 2. Arnie B. 07:56 PM 5/24/08

   One concept not encountered on these premises is that of gravity acting on photons from a position ahead of the photon.
   From a position posterior to a photons path a black hole is known. Gravity sources laying alongside a photons path provides gravitational lensing.
   What of gravity anterior to a photons path, would acceleration not effect the photon as well? Would that effect be, since the photon is traveling at velocity limits, the stretching of the photons wavelength? Would the dopler shift noted by Hubble be accounted for by gravitational acceleration just as well as expansion of the universe? Both are distance/time dependent.
   Seems that gravitationl acceleration on the photon over time may be a better answer than shifting one universe, but then ...
   
   --
   Edited by Arnie B. at 05/24/2008 1:26 PM

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3. 3. Arnie B. 08:29 PM 5/24/08

   One concept not encountered on these premises is that of gravity acting on photons from a position ahead of the photon.
   From a position posterior to a photons path a black hole is known. Gravity sources laying alongside a photons path provides gravitational lensing.
   What of gravity anterior to a photons path, would acceleration not effect the photon as well? Would that effect be, since the photon is traveling at velocity limits, the stretching of the photons wavelength? Would the dopler shift noted by Hubble be accounted for by gravitational acceleration just as well as expansion of the universe?
   Seems that gravitationl acceleration on the photon over time is a better answer than shifting one universe, but then ...

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4. 4. jmilliken 01:39 PM 10/8/11

   It is all very intriguing. Given the original view that gravity would put a brake on expansion would this not suggest a weakening of the force in the region of the 1a Supernova?

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5. 5. hybrid 05:42 PM 10/8/11

   A better fit for all the "blacks" is "The Dynamic Ether" from Kunaki. One single assumption takes the mystery out all of the above and includes a proposal for a two fold type gravity, the tidal process, and even suggests a science based religion. Einstein could have been right for the wrong reasons, and Michelson/Moreley could have been wrong for the right reasons.

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6. 6. hybrid 04:44 PM 10/10/11

   Michelson was taking readings in a closed system, Since the ether, according to the Dynamic Ether, converges on and travels with the earth.
   'Michelson could have been trying, as it were, "to find the drag of the air with a pitot tube in a balloon."
   He was wrong to conclude there was no (measurable) ether, but was right to accept his readings for a nonexistent static ether.
   

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7. 7. demitrickster in reply to hybrid 03:21 AM 10/22/11

   I've seen you make a few posts about this "Dynamic Ether" by Kunaki. What is it exactly? All I found by on Google where more of your posts.

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8. 8. hybrid in reply to demitrickster 05:58 PM 10/22/11

   I am working on a link, sorry about that.

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9. 9. hybrid 06:16 PM 10/22/11

   Perhaps the Solar Wind could be ingeniously harnessed for some solar sailing. After all the Earth's magnetic field interacts and diverts the flow, so why not figure out the why's and wherefores to allow the space boat to tack, run and close haul itself upwind towards the sun. Get Michio Kaku busy on the good ship "Sollipop"

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10. 10. hybrid 02:56 AM 10/23/11

    The expanding universe
    quote -- "Perlmutter’s SCP team announced the discovery first, but Schmidt’s High-Z team beat the SCP group in publishing the finding."
    High-Z made a big mistake by informing SCP of their discovery, who then hastily got into the act (it was probably unnoticed in their own data) and before High-Z could formally publish, Perlmutter did his sooner stuff.
    -- Hitting all the media sources under the sun.
    My guess is that SCP's poor science threw out any data that did not show the universe was slowing down, and only found the opposite motion when Schmidt told him to check his data.
    Sorry for being meanish but there you are.

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