Part 12 (2/2)

Each satellite will e the laser bea from the other two satellites, each satellite will be able to construct an interference pattern of light If a gravity wave disturbs the laser beae the interference pattern, and the satellite will be able to detect this disturbance (The gravity wave does not make the satellites vibrate It actually creates a distortion in the space between the three satellites) Although the laser bea They will be able to detect vibrations to within one part in a billion trillion, corresponding to a shi+ft 1/100 the size of an atoravity wave froht-years, which covers most of the visible universe

LISA has the sensitivity to potentially differentiate between several ”prebig bang” scenarios One of the hottest topics in theoretical physics today is calculating the characteristics of the prebig bang universe At present, inflation can describe quite well how the universe evolved once the big bang took place But inflation cannot explain why the big bang took place in the first place The goal is to use these speculative ravity radiation e theoriesradiation predicted by the Big Splat theory, for example, differs from the radiation predicted by soht be able to rule out several of these theories Obviously, these prebig bang models cannot be tested directly, since they involve understanding the universe before the creation of time itself, but we can test them indirectly since each of these theories predicts a different radiation spectru

Physicist Kip Thorne writes, ”So Bang singularity will be discovered There will ensue an era, lasting at least until 2050These efforts will reveal intiularity, and will thereby verify that soravity”

If LISA is unable to differentiate between different prebig bang theories, its successor, the Big Bang Observer (BBO) ht It is tentatively scheduled for launch in 2025 The BBO will be able to scan the entire universe for all binary syste neutron stars and black holes with mass less than one thousand tioal is to analyze gravity waves e In this sense, the BBO is specifically designed to probe the predictions of the inflationary big bang theory

The BBO is son It will consist of three satellites ether in an orbit around the sun, separated from each other by 50,000 kilometers (these satellites will be much closer to one another than LISA's satellites) Each satellite will be able to fire a 300-watt laser bearavity wave frequencies between LIGO and LISA, filling an iravity waves froravity waves of frequency 10 microhertz to 10 millihertz BBO will be able to detect frequencies that include both ranges) ”By 2040 ill have used those laws [of quantuh-confidence answers to What caularity, or was there even such a thing as a 'before'? Are there other universes? And if so, how are they related to or connected to our own universe?Do the laws of physics perhly advanced civilizations to create and maintain wormholes for interstellar travel, and to create time machines for backward time travel?”

The point is that in the next few decades there should be enough data pouring in froravity wave detectors in space to differentiate between the various prebig bang theories

THE END OF THE UNIVERSE

The poet T S Eliot asked the question, Will the universe die with a bang or a whimper? Robert Frost asked, Will we all perish in fire or ice? The latest evidence points to the universe dying in a Big Freeze, in which teent life will be extinguished But can we be sure?

Some have raised another ”impossible” question Hoe ever know the ultimate fate of the universe, they ask, since this event is trillions upon trillions of years in the future? Scientists believe that ”dark energy” or the energy of the vacuualaxies apart at an ever increasing rate, indicating that the universe seems to be in a runaway mode Such an expansion would cool the te Freeze But is this expansion temporary? Could it reverse itself in the future?

For exa Splat scenario, in which two membranes collide and create the universe, it appears as if the membranes can collide periodically If so, then the expansion that appears to lead to a Big Freeze is only a te the current acceleration of the universes is dark energy, which in turn is probably caused by the ”cosical constant” The key, therefore, is to understand this y of the vacuum Does the constant vary with time, or is it really a constant? At present, no one knows for sure We know fro the Earth that this cos the current acceleration of the universe, but we don't know if it is permanent or not

This proble back to 1916 when Einstein first introduced the coseneral relativity the previous year, he worked out the cosical implications of his own theory Much to his surprise, he found that the universe was dynamic, that it either expanded or contracted But this idea see the Bentley paradox, which had bedeviled even Newton Back in 1692 the Reverend Richard Bentley wrote Newton an innocent letter with a devastating question If Newton's gravity was always attractive, Bentley asked, then why doesn't the universe collapse? If the universe consists of a finite collection of stars that ether and the universe should collapse into a fireball! Neas deeply troubled by this letter, since it pointed out a key flaw in his theory of gravity: any theory of gravity that is attractive is inherently unstable Any finite collection of stars will inevitably collapse under gravity

Nerote back that the only way to create a stable universe was to have an infinite and unifor pulled in all directions, so that all the forces cancel out It was a clever solution, but Neas sh to realize that such stability was deceptive Like a house of cards, the tiniest of vibrations would cause the whole thing to collapse It was ”htest perturbations caused it to crash Newton concluded that God was necessary to periodically nudge the stars a bit so the universe did not collapse

In other words, Newton saw the universe as a gigantic clock, wound up by God at the beginning of ti automatically ever since, without divine intervention However, according to Newton, God was necessary to tweak the stars once in a while so the universe did not collapse into a fireball

When Einstein stumbled on the Bentley paradox in 1916, his equations correctly told hi or contracting-and that a static universe was unstable and would collapse due to gravity But the astronomers insisted at that ti So Einstein, bowing to the observations of the astronoravity force that pushed the stars apart to balance the gravitational pull causing the universe to collapse (This antigravity force corresponded to the energy contained within the vacuum In this picture even the vast ee quantities of invisible energy) This constant would have to be chosen very precisely in order to cancel out the attractive force of gravity

Later, when Edwin Hubble showed in 1929 that the universe was, in fact, expanding, Einstein would say that the cosreatest blunder” Yet now, seventy years later, it appears as if Einstein's ”blunder,” the cosest source of energy in the universe, y content of the universe (By contrast, the higher elements that make up our bodies constitute only 03 percent of the universe) Einstein's blunder will likely determine the ultiical constant co of tih to cause the universe to inflate, creating the big bang Then it suddenly disappeared, for reasons that are unknown (The universe was still expanding during this period, but at a slower pace) And then, about eight billion years after the big bang, the antigravity force resurfaced again, causing the galaxies to push out and causing the universe to accelerate once again

So is it ”impossible” to determine the ultimate fate of the universe? Perhaps not Most physicists believe that quantuical constant A naive calculation, using a priical constant is off by a factor of 10120 This is the greatest mismatch in the history of science

But there is also a consensus a physicists that this anoravity Since the cosical constant arises via quantu-a theory that will allow us to calculate not just the Standard Model, but also the value of the cosical constant, which will determine the ulti is necessary to determine the ultimate fate of the universe The irony is that some physicists believe that it is i

A THEORY OF EVERYTHING?

As Icandidate for a ”theory of everything,” yet there are opposing ca theory lives up to this claimark write, ”In 2056, I think you'll be able to buy a T-shi+rt on which are printed equations describing the unified physical laws of our universe” On the other hand, there is an e bandwagon has yet to deliver No matter how many breathless articles or TV docu theory, it has yet to produce a single testable fact, so, rather than a theory of everything, claim the critics The debate heated up considerably in 2002 when Stephen Hawking switched sides, quoting the incoht even bethat the debate has pitted physicist against physicist, because the goal is so lofty, if elusive The quest to unify all the laws of nature has tantalized and lured philosophers and physicists alike for millennia Socrates hi-to know the explanation of everything, why it comes to be, why it perishes, why it is”

The first serious proposal for a theory of everything dates back to about 500 BC, when the Greek Pythagoreans are credited with deciphering thethe nodes and vibrations of a lyre string, they showed that music obeyed remarkably simple mathematics They then speculated that all of nature could be explained in the hars back the dreaiants of twentieth-century physics tried their luck with a unified field theory But, as Freeround of physics is littered with the corpses of unified theories”

In 1928 the New York Tireat discovery; resents intrusion” The news story helped spark athat hipped up to a feverish pitch Headlines blared ”Einstein is amazed at stir over theory Holds 100 journalists at bay for a week” Scores of journalists swaril, waiting to catch a glirab a headline Einstein was forced to go into hiding

Astronoton wrote to Einstein: ”You reat departes) has posted on itsyour paper (the six pages pasted up side by side) so that passers-by can read it all through Large crowds gather around to read it” (In 1923 Eddington proposed his own unified field theory on which he worked tirelessly for the rest of his life, until he died in 1944) In 1946 Erwin Schrodinger, one of the founders of quantum mechanics, held a press conference to propose his unified field theory Even Ireland's Prime Minister, Eamon De Valera, showed up When a reporter asked hier replied, ”I believe I a” (Schrodinger was humiliated when Einstein politely pointed out the errors in his theory) The harshest of all critics of unification was physicist Wolfgang Pauli He chided Einstein, saying, ”What God has torn asunder, let no ether” He mercilessly put down any half-baked theory with the quip: ”It's not even wrong” So it is ironic that the supre In the 1950s he proposed his own unified field theory with Werner Heisenberg

In 1958 Pauli presented the Heisenberg-Pauli unified theory at Columbia University Niels Bohr was in the audience, and he was not impressed Bohr stood up and said, ”We in the back are convinced that your theory is crazy But what divides us is whether your theory is crazy enough” The criticis Since all the obvious theories had been considered and rejected, the true unified field theory -Pauli theory was simply too conventional, too ordinary, too sane to be the true theory (That year Pauli was disturbed when Heisenberg commented on a radio broadcast that only a few technical details were left in their theory Pauli sent his friends a letter with a blank rectangle, with the caption, ”This is to show the world I can paint like titian Only technical details are ”) CRITICISMS OF STRING THEORY

Today the leading (and only) candidate for a theory of everything is string theory But, again, a backlash has arisen Opponents claiet a tenured position at a top university you have to work on string theory If you don't you will be uneood for physics

I smile when I hear this criticism, because physics, like all human endeavors, is subject to fads and fashi+ons The fortunes of great theories, especially on the cutting edge of hue, can rise and fall like he theory was historically an outcast, a renegade theory, the victi theory was born in 1968, when two young postdocs, Gabriel Veneziano and Mahiko Suzuki, stumbled on a formula that seemed to describe the collisions of subatomic particles Quickly it was discovered that this marvelous fors But by 1974 the theory was dead in its tracks A new theory, quantu interaction, was a juggernaut flattening all other theories People left string theory in droves to work on QCD All the funding, jobs, and recognition went to physicists working on the quark model

I remember those dark years well Only the foolhardy or the stubborn persisted in working on string theory And when it becas could vibrate only in ten di pioneer John Schwarz at Cal Tech would sometimes bump into Richard Feynman in the elevator Ever the joker, Feynman would ask, ”Well, John, and how many dimensions are you in today?” We used to joke that the only place to find a string theorist was in the unemployment line (nobel laureate Murray Gell-Mann, founder of the quarktheorists and created a ”nature preserve for endangered string theorists” at Cal Tech so people like John wouldn't lose their jobs) Given that today sotheory, Steve Weinberg has written, ”String theory provides our only present source of candidates for a final theory-how could anyone expect thattheorists would not work on it?”

IS STRING THEORY UNTESTABLE?

Onetheory today is that it is untestable It would take an atoalaxy to test this theory, critics clailects the fact that most science is done indirectly, not directly No one has ever visited the sun to do a direct test, but we know it is en because we can analyze its spectral lines

Or take black holes The theory of black holes dates back to 1783, when John Michell published an article in the Philosophical Transactions of the Royal Society He claiht emitted from such a body would be ravity” Michell's ”dark star” theory languished for centuries because a direct test was i that such a dark star could not form by natural means The criticism was that these dark stars were inherently untestable because they were, by definition, invisible Yet today the Hubble space Telescope has given us gorgeous evidence of black holes We now believe that billions of the black holes could exist in our own galaxy But the point is that the evidence for black holes is all indirect; that is, we have gathered infor the accretion disk that swirls around them

Furthermore, many ”untestable” theories ultimately become testable It took two thousand years to prove the existence of atoms after they were first proposed by De Boltz in that theory, yet today we have gorgeous photographs of atoms Pauli himself introduced the concept of the neutrino in 1930, a particle so elusive it can pass through blocks of solid lead the size of an entire star system and not be absorbed Pauli said, ”I have committed the ultimate sin; I have introduced a particle that can never be observed” It was ”impossible” to detect the neutrino, so it was considered little more than science fiction for several decades Yet today we can produce beams of neutrinos

There are, in fact, a number of experiments that will provide, physicists hope, the first indirect tests of string theory: The Large Hadron Collider (LHC) h to produce ”sparticles,” or superparticles, which are the higher vibrations predicted by superstring theory (as well as by other supersymmetric theories)

As I mentioned earlier, in 2015 the Laser Interferometer space Antenna (LISA) will be launched in space LISA and its successor, the Big Bang Observer, ” theories, including versions of the string theory

A nuher di at deviations from Newton's famed inverse-square law at the milliravity should fall by the inverse cube, not the inverse square) The latest version of string theory (M-theory) predicts there are eleven di to detect darkin a cos theory makes specific, testable predictions about the physical properties of dark her vibration of the string (eg, the photino)

It is hoped that a series of additional experi, on neutrino polarization in the south pole) will detect the presence ofanoies can easily exceed those of the LHC Cos frontier beyond the Standard Model

And there are so was so explosive that perhaps a tiny superstring was blown up into astronomical proportions As physicist Alexander Vilenkin of Tufts University writes, ”A very exciting possibility is that superstringscan have astronomical dimensionsWe would then be able to observe the theory” (The probability of finding a huge, relic superstring that was blown up during the big bang is quite s helped to spark interest in a theory of everything with his lecture entitled ”Is the End in Sight for Theoretical Physics?” in which he said, ”We may see a complete theory within the lifetime of some of those present here” He claimed that there was a fifty-fifty chance that the final theory would be found in the next twenty years But when the year 2000 arrived and there was no consensus on the theory of everything, he changed hisit in another twenty years

Then in 2002 Hawking changed histhat Godel's incoinal line of thinking He wrote, ”Some people will be very disappointed if there is not an ultimate theory that can be for to that caed my mindGodel's theorem ensured there would always be a job for mathematicians I think M-theory will do the saument is an old one: since e of physics is mathematics, there will always be true physical statements that are forever beyond our reach, and hence a theory of everything is not possible Since the inco all true state forever beyond our reach

Freeman Dyson said it eloquently when he wrote, ”Godel proved the world of pure mathematics is inexhaustible; no finite set of axioms and rules of inference can ever encoous situation exists in the physical world If my view of the future is correct, it means that the world of physics and astronoo into the future, there will always be new things happening, new infor in, neorlds to explore, a constantly expanding domain of life, consciousness, and ic this way: ”Science is based on mathematics; mathematics cannot discover all truths; therefore science cannot discover all truths”