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Trouble with physics: The roots of reality

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Trouble with physics: The roots of reality


What makes us so sure that mathematics can reveal nature's deepest workings, asks cosmologist Brian Greene

In the late 1800s, when James Clerk Maxwell realised that light was an electromagnetic wave, his equations showed that light's speed should be about 300,000 kilometres per second. This was close to the value experimenters had measured, but Maxwell's equations left a nagging loose end: 300,000 kilometres per second relative to what? At first, scientists pursued the makeshift resolution that an invisible substance permeating space, the aether, provided this unseen standard of rest.


It was Einstein who in the early 20th century argued that scientists needed to take Maxwell's equations more seriously. If Maxwell's equations did not refer to a standard of rest, then there was no need for a standard of rest. Light's speed, Einstein forcefully declared, is 300,000 kilometres per second relative to anything. The details are of historical interest, but I'm describing this episode for a larger point: everyone had access to Maxwell's mathematics, but it took the genius of Einstein to embrace it fully. His assumption of light's absolute speed allowed him to break through first to the special theory of relativity overturning centuries of thought regarding space, time, matter and energy and eventually to the general theory of relativity, the theory of gravity that is still the basis for our working model of the cosmos.


The story is a prime example of what the Nobel laureate Steven Weinberg meant when he wrote: Our mistake is not that we take our theories too seriously, but that we do not take them seriously enough. Weinberg was referring to another great breakthrough in cosmology, the prediction by Ralph Alpher, Robert Herman and George Gamow of the existence of the cosmic microwave background radiation, the afterglow of the big bang. This prediction is a direct consequence of general relativity combined with basic thermodynamics. But it rose to prominence only after being discovered theoretically twice, a dozen years apart, and then being observed through a benevolent act of serendipity.


To be sure, Weinberg's remark has to be applied with care. Although his desk has played host to an inordinate amount of mathematics that has proved relevant to the real world, far from every equation with which we theorists tinker rises to that level. In the absence of compelling experimental results, deciding what mathematics should be taken seriously is as much art as it is science.


Deciding which mathematics to take seriously is as much art as it is science


Einstein was a master of that art. In the decade after his formulation of special relativity in 1905, he became familiar with vast areas of mathematics that most physicists knew little or nothing about. As he groped towards general relativity's final equations, Einstein displayed a rare skill in moulding these mathematical constructs with the firm hand of physical intuition. When he received the news that observations of the 1919 solar eclipse confirmed general relativity's prediction that star light should travel along curved paths, he noted that had the results been different, he would have been sorry for the dear Lord, since the theory is correct.


I'm sure that convincing data contravening general relativity would have changed Einstein's tune, but the remark captures well how a set of mathematical equations, through their sleek internal logic, their intrinsic beauty and their potential for wide-ranging applicability, can seemingly radiate reality. Centuries of discovery have made abundantly evident the capacity of mathematics to reveal secreted truths about the workings of the world; monumental upheavals in physics have emerged time and again from vigorously following the lead of mathematics.


Nevertheless, there was a limit to how far Einstein was willing to follow his own mathematics. He did not take the general theory of relativity seriously enough to believe its prediction of black holes, or of an expanding universe. Others embraced Einstein's equations more fully than he, and their achievements have set the course of cosmological understanding for nearly a century. Einstein instead in the last 20 years or so of his life threw himself into mathematical investigations, passionately striving for the prized achievement of a unified theory of physics. Looking back, one cannot help but conclude that during these years he was too heavily guided some might say blinded by the thicket of equations with which he was constantly surrounded. Even Einstein sometimes made the wrong decision regarding which equations to take seriously and which to not.


Quantum mechanics provides another case study of this dilemma. For decades after Erwin Schrödinger wrote down his equation for how quantum waves evolve in 1926, it was viewed as relevant only to the domain of small things: molecules, atoms and particles. But in 1957, Hugh Everett echoed Einstein's charge of a half century earlier: take the mathematics seriously. Everett argued that Schrödinger's equation should apply to everything because all things material, regardless of size, are made from molecules, atoms and subatomic particles that evolve according to probabilistic rules. Applying this logic revealed that it is not just experiments that evolve in this way, but experimenters, too. This led Everett to his idea of a quantum multiverse in which all possible outcomes are realised in a vast array of parallel worlds.


More than 50 years later, we still do not know if his approach is right. But by taking the mathematics of quantum theory seriously fully seriously he may have had one of the most profound revelations of scientific exploration. The multiverse in various forms has since become a pervasive feature of much mathematics that purports to offer us a deeper understanding of reality. In its furthermost incarnation, the ultimate multiverse, every possible universe allowed by mathematics corresponds to a real universe. Taken to this extreme, mathematics is reality.


If some or all of the mathematics that has compelled us to think about parallel worlds proves relevant to reality, Einstein's famous query whether the universe has the properties it does simply because no other universe is possible would have a definitive answer: no. Our universe is not the only one possible. Its properties could have been different, and indeed the properties of other member universes may well be different. If so, seeking a fundamental explanation for why certain things are the way they are would be pointless. Statistical likelihood or plain happenstance would be firmly inserted in our understanding of a cosmos that would be profoundly vast.


I don't know if this is how things will turn out. No one does. But it is only through fearless engagement that we can learn our limits. Only through rational pursuit of theories, even those that whisk us into strange and unfamiliar domains by taking the mathematics seriously do we stand a chance of revealing the hidden expanses of reality.


This article appeared in print under the headline Roots of reality


Brian Greene is a theoretical physicist at Columbia University in New York. This article is adapted from his book The Hidden Reality (Allen Lane, 2011)


Trouble with physics: Seven experiments to change it all


With theory stalled, the next breakthrough in physics is likely to come from an experiment. We introduce seven potential game-changers

With theory at an impasse, the next breakthrough in physics is likely to come from an experiment. We introduce seven potential game-changers, starting with the behemoth that's soon to get bigger…


The Higgs boson is (probably) in the bag, but the Large Hadron Collider has plenty more to give. Starting late in 2014, the plan is to double the energy of the proton collisions at CERN's particle smasher.


That should be enough to produce particles predicted by next-generation theories such as supersymmetry. But it is a multibillion-dollar gamble. If it does not pay off, it is back to scrabbling around in cosmic rays or measuring tiny atomic effects to find answers.


Richard Webb


The Planck probe


Radiation left over from the big bang contains vital clues about the early universe. The most detailed maps of it are coming from the European Space Agency's Planck satellite, launched in 2009. It can capture the radiation precisely enough to measure cosmological quantities without making many theoretical assumptions, detect the rippling of gravitational waves and test various models of the inflation thought to have occurred during the big bang. It will even let us explore ideas outside of our standard cosmology, such as parallel worlds.


Valerie Jamieson


Advanced LIGO


General relativity predicts that ripples in space-time should constantly be passing through Earth. From 2014 Advanced LIGO, an upgrade of an existing gravitational-wave detector in the US (pictured), will use laser “rulers” several kilometres long to spy spatial disturbances equivalent to Earth moving one-tenth of an atomic diameter closer to the sun.


If it sees something, it will be the crowning triumph of Einstein's relativity. If it doesn't, it is back to the drawing board with our theories of gravity.


Richard Webb


LISA Pathfinder


The European Space Agency's LISA Pathfinder mission will primarily test gravitational-wave detectors, but from next year it could also confirm whether gravity is all general relativity says it is. By flying through the “saddle point” where the Earth and the sun's gravity cancel out, the craft might probe whether Einstein's theory still holds when gravitational accelerations are incredibly small. If it does, these gravitational lacunae will be the last resting place of other occasionally fashionable theories, such as Modified Newtonian dynamics (MOND).


Stuart Clark


Dark matter searches


Theory points to dark matter being made of so-far-unseen weakly interacting massive particles, known as WIMPs. Over a dozen exquisitely sensitive experiments have been built specifically to catch these slippery customers. Three – DAMA/LIBRA (pictured), CoGeNT and CRESST – have seen things that look suspiciously like them. Others have ruled out the same particles entirely. The trouble is we know too little about what we are looking for. We need more data and additional experiments to understand the experiments.


Valerie Jamieson


Neutrino factories


Neutrino experiments are a hit-and-miss affair. The properties of the ghostly particles are ill-defined, and they interact so rarely that vast floods of them are needed for us to spot anything. The solution could be nuSTORM, a proposed “factory” that will churn out precisely controlled beams of neutrinos or their antimatter counterparts, antineutrinos. That could at last pin down their nature and the number of varieties they come in – and so settle whether any additional types of non-interacting “sterile” neutrinos exist.


Valerie Jamieson


Quantum theory in space


Experiments beaming photons over sometimes hundreds of kilometres have so far only confirmed quantum theory's outrageous predictions of weird correlations and entanglements between the particles.


Soon the ante will be upped with plans to beam quantum transmissions via satellite between continents. It's a first step to testing quantum theory in space over distances at which relativity's warping becomes significant – and so seeing what happens when those two great and incompatible theories collide.


Richard Webb



the study of the laws that determine the structures of the universe with reference to the matter and energy of which it consist.


It is concerned not with chemical changes that occur but with the forces that exist between objects and the interrelationship between matter and energy.


Traditionally,the study was divided into separate fields:

heat, light, sound, electricity and magnetism, and mechanics (classical physics).


Since the turn of the century, however, quantum mechanics and relativistic physics have become increasingly important ; the growth of modern physics has been accompanied by the studies of atomic physics, nuclear physics and particle physics.


the physics of astronomical bodies and their interactions is know as astrophysics,the physics of the earth is know as geophysics,and the study of the physical aspects of biology is called biophysics.




The study of physics by formulating and analyzing theories that describe natural processes.


Theoretical physics is complementary to the study of physics by experiment,which is called experimental physics.


A large of theoretical physics consist of analyzing the results of experiments to see whether or not they obey particular theories.


The branch of theoretical physics concerned with the mathematical aspects of theories in physics is called mathematical physics.


another thing is,

anthropocentric whether we like it or not

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Quantum physics is a subset of physics. Basic math and/or logic dictates that if you discuss quantum physics, you are discussing physics.

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