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Nobel Dreams: 2011 Physics Prize Honors Accelerating Universe


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A few years ago, soon after moving to Los Angeles, an old grad school buddy of the Time Lord came to town, Brian Schmidt, and we took him to a nearby tapas eatery for nibbles and pisco sours. I remember they were shooting a scene from a Will Smith movie that night, so nearby storefronts were riddled with fake bullet holes, and the odd fake gunfire and explosion interrupted our conversation. Unfazed, Brian regaled us with tales of his life in Australia, where he juggles research with running his very own winery — hence his Twitter handle, @CosmicPinot.

After saying farewell, I commented to the Time Lord as we walked back home how much I liked Brian: “You have really nice friends.” (It’s true; pretty much all of the Time Lord’s pals are delightful, but then, I’m partial to physicists.) He agreed, and added, “And you know what else? He will absolutely win the Nobel Prize some day.”

That day has arrived, perhaps a bit earlier than even Schmidt and his colleagues on the research expected. This morning it was announced that the 2011 Nobel Prize in Physics had been awarded to Saul Perlmutter of the University of California, Berkeley; Brian Schmidt of the Australian National University in Weston Creek; and Adam Riess, an astronomy professor at Johns Hopkins University and the Space Telescope Science Institute, “for their studies of exploding stars that revealed that the expansion of the universe is accelerating.”

Schmidt was the leader of the High-Z Supernova Search Team and Reiss was lead author on the resulting paper; Perlmutter was the leader of the Supernova Cosmology Project and also lead author on that resulting paper. They’ve had a friendly mock rivalry going on ever since. (Photo: Schmidt, left, dukes it out with Perlmutter, right, over who made the best measurement of the rate of expansion. Credit: Texas A&M cosmologist Nicholas Suntzeff.)

It’s a fitting coda to what turns out to be just the beginning of an epic saga of the quest to unlock the mysteries of the cosmos. Because the most likely explanation we have (so far) for this observed acceleration is a mysterious thing called dark energy that makes up a whopping 73% of all the “stuff” in the universe.

Einstein’s Fudge Factor

Once upon a time, physicists believed the cosmos was static and unchanging, a celestial clockwork mechanism that would run forever. When Albert Einstein was forming his theory of general relativity in 1917, his calculations indicated that the universe should be expanding. But all the observations up to then showed a static universe. So he figured his calculations were incorrect, and introduced a mathematical “fudge factor” into his equations, known as the cosmological constant, or lambda. It implied the existence of a repulsive force pervading space that counteracts the gravitational attraction holding the galaxies together. This balanced out the “push” and “pull” so that the universe would indeed be static.

Einstein should have trusted his instincts. Twelve years later, Edwin Hubble was studying distant galaxies, and noticed an intriguing effect in the light they emitted: it had a pronounced “Doppler shift” toward the red end of the electromagnetic spectrum. Basically, when a light source is moving towards an observer, the wavelength of its emitted light compresses and shifts to the blue end of the spectrum. When moving away from the observer, the wavelength stretches, and the light shifts to the red end of the spectrum.

Hubble reasoned that this could only be happening if the light were traveling across space that is expanding. The conclusion was inescapable. Einstein’s original equations had been correct, and there was no need for a cosmological constant. The cosmos was still expanding. That’s why Einstein famously denounced lambda as his “greatest blunder.”

That discovery turned cosmology on its head. If the universe were still expanding, scientists reasoned, eventually the attractive force of gravity would slow down the rate of expansion. They spent the next 70 years trying to measure that rate. If they knew how the rate of expansion was changing over time, they could deduce the shape of the universe. And its shape was believed to determine its fate.

Matter curves space and time around it and gives rise to what we recognize as gravity. The more matter there is, the stronger the pull of gravity, and the more space will curve – making it more likely that the current expansion would halt and the universe would collapse back in on itself in a “Big Crunch.” If there’s not enough matter, the pull of gravity would gradually weaken as galaxies and other celestial objects move farther apart, and the universe would expand forever with essentially no end. A flat universe, with just the right balance of matter, would mean that the expansion will slow down indefinitely, without recollapsing.

A flat universe was the favored option; scientists just needed to precisely measure the acceleration rate to confirm the prediction.

Faster, Faster….

Once again, Einstein was a bit too hasty in dismissing his work. In 1998, two separate teams of physicists measured the change in the universe’s expansion rate, using distant supernovae as mileposts: one led by Perlmutter, the other by Schmidt. The Time Lord shared an office with Schmidt back in the early 1990s. As he tells it in his book, From Eternity to Here:

I was the idealistic theorist and he was the no-nonsense observer. In those days, when the technology of large-scale surveys in astronomy was just in its infancy, it was a commonplace belief that measuring the cosmological parameters was a fool’s errand, doomed to be plagued by enormous uncertainties that would prevent us from determining the size and shape of the universe with anything like the precision we desired.

Brian and I made a bet concerning whether we would be able to accurately measure the total matter density of the universe within 20 years. I said we would; Brian was sure we wouldn’t. We were poor graduate students at the time, but purchased a small bottle of vintage port, to be secreted away for two decades before we knew who had won. Happily for both of us, we learned the answer long before then. I won the bet, due in large part to the efforts of Brian himself. We split the bottle of port on the roof of Harvard’s Quincy House in 2005.

Why supernovae? They’re the best “standard candles” we’ve got. Because they are among the brightest objects in the universe, these exploding stars can help astronomers determine distances in space.

By matching up those distances with how much the light from a supernova has shifted, the two teams could calculate how the expansion rate has changed over time. Light that began its journey across space from a source 10 billion years ago would have a red shift markedly more pronounced than the light that was emitted from a source just 1 billion years ago.

When Hubble made his 1929 measurements, the farthest red-shifted galaxies were roughly 6 million light years away. If expansion was now slowing, supernovae in those distant galaxies should appear brighter and closer than their red shifts would suggest.

Instead, just the opposite was true. At high red shifts, the most distant supernovae are dimmer than they would be if the universe were slowing down. The only plausible explanation for this is that instead of gradually slowing down, the expansion of the universe is speeding up.

It was bizarre and completely unexpected. Since 1998, cosmologists have been grappling a whole new set of questions implied by that momentous discovery, the foremost of which is the makeup of the mysterious dark energy that appears to be winning the cosmic tug-of-war.

And once again, the discovery turned cosmology on its head. Now the story goes something like this: very early in the universe’s existence, dark matter dominated. Everything was closer together, so its density was higher than that of the dark energy, and its gravitational pull was stronger. This led to the clumping that formed early galaxies. But as the universe continued to expand, the dark matter density, and hence the gravitational pull, decreased until it was less than that of the dark energy. So instead of the expected slow-down in the expansion rate, the now-dominant dark energy began pushing the universe apart at ever-faster rates.

Where does this dark energy come from? That’s the big question. But it’s a testament to Einstein’s genius that even his blunders prove to be significant. Remember his “fudge factor,”  Lambda implied the existence of a repulsive form of gravity, and the simplest example of that is the vacuum energy. Quantum physics holds that even the emptiest vacuum is teeming with energy in the form of “virtual” particles that wink in and out of existence, flying apart and coming together in an intricate quantum dance. This roiling sea of virtual particles could give rise to dark energy, giving the universe a little extra push so that it can continue accelerating.

The problem is that the numbers don’t add up. The quantum vacuum contains too much energy: roughly 10120 times too much. So the universe should be accelerating much faster than it is. An alternative theory proposes that the universe may be filled with an even more exotic, fluctuating form of dark energy dubbed “quintessence.” Yet all the observations to date indicate that the dark energy is constant, not fluctuating.

So scientists must consider even more possibilities. The dark energy could be the result of the influence of unseen extra dimensions predicted by string theory. Alternatively, the dark energy could be due to neutrinos – the lightest particles of matter – interacting with hypothetical particles called “accelerons.” Some scientists have theorized that dark matter and dark energy emanate from the same source – they just don’t know what that source might be. Yet it’s just as likely that there is no connection, and the two are very different things. Or perhaps there is no such thing as dark energy, and we need to revise Einstein’s general theory of relativity, and/or devise a theory of quantum gravity.

Scientists love to explore the unknown, so these are exciting times for cosmologists. Congratulations to Schmidt, Reiss and Perlmutter for a well-deserved honor — and here’s to the future Nobel-worthy discoveries yet to be made!

Jennifer Ouellette About the Author: Jennifer Ouellette is a science writer who loves to indulge her inner geek by finding quirky connections between physics, popular culture, and the world at large. Follow on Twitter @JenLucPiquant.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. eihab 3:45 am 10/6/2011

    Does this discovery put an end to the big crunch theory?
    thanks.

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  2. 2. HubertB 8:36 pm 10/6/2011

    This could simply be a validation of a prediction made at the Leningrad Institution some 35 years ago based on the gravitational section of The Theory of Relativity. The differential equations in the gravitational section produced the idea that a gravity wave front would be produced every time mass was lost in a nuclear explosion. The chaos of the gravity wave front would make it a repulsive force. However, when it got halfway around the universe, the gravity wave front would turn into a gravon and become an attractive force.
    So, the Leningrad prediction was that the mass within a galaxy times the gravitational constant would be powerful enough to hold the galaxy together. However, as galaxies separated and the force of gravity dropped off as the square of the distance, then the power of the gravity waves would begin to accelerate the rate of separation. Finally, the gravity waves would become attractive and reverse.
    I have no idea why this was not mentioned.

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  3. 3. Arcturus_Sky 6:35 am 10/7/2011

    “The only plausible explanation for this is that … the expansion of the universe is speeding up.”

    Never has a Noble prize in Physics been awarded based upon experimental results with such little theoretical explanation. There is in fact no plausible explanation as to why the universe is possibly speeding up. Yes, there are many theories out there, “dark energy”, quintessence, ekpyrotic scenario, etc., but there is no definitive physics that explains such a result. Heck, physicists are still working on why the universe is expanding at all. Yes there is the big bang and inflation and all that but the primordial cause for expansion as we know it is still something of a mystery.

    The astronomers that won this prize did a remarkable job collecting the data that they did and observing that the velocity curves did not fit what was expected. But such an unexpected result does not automatically mean the universe is accelerating when astronomers still do not know what “dark energy” or even dark matter is. There could easily be another explanation of these results that has not been considered yet. Until then we are still in the dark.

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  4. 4. Vaggelis Talios 7:02 am 10/7/2011

    Congratulations to Saul Perlmutter, Adam Riess and Brian Schmidt, for the nobel prize.
    I agree to the accelerating expansion of the Universe. In recent times comes to light theories, which reverse the current model of physics. In my book “From the inside of quarks and up to beyond the universe”, page 125, I describe an interesting, new proposal on the cause, of the accelerating expansion of the Universe as follows:

    “In the beginning, along with matter, antimatter is created. Then the matter and the antimatter, creates sets of masses of matter and sets of masses of antimatter, which are formed in, solar systems and galaxies of matter and sets of solar systems and galaxies of antimatter. Between the systems of matter and antimatter there is developed a repulsion. This repulsion is dynamically creates the accelerating expansion of the universe, -or better the acceleration of the universes and anti universes-”. More details there are in my book.

    Ι’am writing these few lines, to highlight the case that besides ‘dark matter’, there are many other reasons, for which, we can attribute the phenomenon, of the acceleration of the expansion of the universe. There is no, any particular reasons, after the award ceremony, we all start, to look for ‘dark matter’ or ‘dark energy’.

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  5. 5. Philippe00001 12:39 pm 10/7/2011

    Vaggelis Talios: Following on your matter and antimatter repulsing each other….
    I always thought that matter and antimatter were identical in nearly everything except charge: both have +ve mass, one is not the -ve of the other.
    Is the term ‘Antimatter’ a misnomer… it should say ‘anticharge’
    The particles should therefore attract each other.
    They then combine and give off energy (also +ve).

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  6. 6. Vaggelis Talios 7:49 pm 10/7/2011

    Philippe00001. Based on the existing data of science, you’re absolutely right. Beware, however, two quite small details:

    -The word matter, are always, a word we corresponded to mass and antimatter to antimass, -not to anticharge – and
    -In terms of atoms, is the opposite that of the charged particles, with the same atoms to be pulled.

    Of course, the same should be done at antiatoms, with the same antiatoms,to be pulled again.
    Following the above considerations, it is perfectly normal to assume that atoms repel antiatoms.
    All this, proves the theory, in my new book, that will be released in 2012.
    I predict, that if science does not understand this very small detail, in the future it will have great adventures.

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  7. 7. wondere 6:21 pm 10/8/2011

    So if space is accelerating, then time is constant or it is accelerating too?

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  8. 8. Vaggelis Talios 6:26 am 10/9/2011

    Wondere. I wonder why, we all get confused with time. The time is time, nothing more or less. I do not know what say several theories, but ‘events’ are those that accelerate or decelerate through the time.

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  9. 9. christinaak 3:32 pm 10/11/2011

    “The dark energy could be the result of the influence of unseen extra dimensions predicted by string theory.” Actually that is what I propose in my book: “The Short Range Anti-gravitational Force and the Hierarchically Stratified Space-time Geometry in 12 Dimensions”. In my book I suggest that the cosmic space-time geometry is hierarchically stratified into 3 strata (1, dark energy with 4 space-time dimensions, 2, dark matter- that oscillates within bottom 8 space-time dimensions, and 3. baryonic matter- which oscillates through the entire 12 space-time dimensional structure). the dark energy stratum of space-time represents the vacuum of space and is filled with dark energy particles that possess a short range repulsive force that will reverse to an attractive force when the universe dies leading to recollapse of the universe. now if it is true that energy can neither be created or destroyed then the acceleration of the expansion of the universe can only be fueled by the conversion of some other form of matter or energy. I suggest that new dark energy particles may be continuosly produced through photon or neutrino decay (during which these particles cease to oscillate through the entire 12 dimensional space-time stucture and instead begin to oscillate within the bottom 4 space-time dimensional structure. when the production of dark energy ceases at the end of the cosmic lifecycle (which will be when photon or neutrino decay has ceased) then the dark energy will reverse from a repulsive to an attractive property. this will then accelerate cosmic collapse. the antigravitational force will halt the contraction of space at a subplength distance throughout infinite space (the universe always remains infinite the only thing that changes is its density-which is inevitably true if there are no singularities and space is quantized) and the universe will reexpand starting a new cycle

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  10. 10. christinaak 5:05 pm 10/12/2011

    I meant to say” The antigravitational force will halt the contraction of space at subplanck length distance throughout infinite space…” (sorry about the typo.) The extra dimensions of time arise as a consequence of the difference in space-time structure between the three strata of space-time. Because each strata possesses variation in the constant c (as well as the constants G and h), then there will be a variation in space contraction, and time dilation as particles oscillate through the multi-stratum structure (this means stratum dependent variations in planck time, and planck temperature as well). There is also a variation in the velocity at which the forces interact between particles within each strata or as particles oscillate within each strata. I suggest this may provide an explanation to how entanglement works (the so-called spooky action at a distance). Because the velocity for c is greater in the lower two strata (as I propose) then particles can communicate at a velocity faster than c as measured in the baryonic matter stratum (as they oscillate through the lower strata) . Like Einstein I believe that there is an underlying reality that explains all of the peculiarities of quantum behavior, and the ideas contained in my book are an attempt to explain that reality.

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