For a long time, scientists believed that space was infinite and rigid, and that time flows universally on... the universe was the perfect stage on which humans could act. Einstein came onto the stage in the early 20th century and posited that time was merely a 4th dimension, and that space and time were actually unified- spacetime. Dr Dijkgraaf then displayed an animation of a 4-dimensional cube being rotated, similar to this video, noting that this is actually a 2-dimensional rendition of a 4-dimensional cube being rotated. He noted that, the retina being flat, the eye doesn't see in three dimensions, but the brain fills in the third dimension when the image is interpreted. Dr Dijkgraaf joked about a colleague who, on seeing a representation of a 4th dimension hypercube casting a shadow onto the third dimension, commented, "It's more simple to see in five dimensions."
Dr Dijkgraaf compared spacetime to a roll of film, with each particular instant being a frame- he displayed a video of two particles moving through spacetime, then displayed an image of the video broken down into a stack of frames, so that the image of the particles' motion appeared as two strands- he noted that everything happens at once in spacetime. He then joked that every formula should fit on a T-shirt, using Einstein's E = mc2 as an example. The equal sign in the formula connects the two sides of the equation, connecting two different worlds- in the Energy/Mass equivalence formula, energy and mass are 'talking to each other'- a small amount of mass can be converted into a vast amount of energy. Walking across the stage, Dr Dijkgraaf noted that he weights more as he moves across the stage (about one millionth more) than he does while he is standing still. He then displayed an image of Einstein's Field Equations:
He noted that, according to General Relativity, mass tells spacetime how to curve and that spacetime tells mass how to move.
Dr Dijkgraaf then presented a basic history of the Theory of General Relativity, noting that Arthur Eddington's 1919 observation of a total solar eclipse (PDF) offered proof that light was deflected by gravity- the stars behind the sun were visible due to this deflection. Einstein quickly became famous after this proof of his Theory of General Relativity, though communications were fairly slow in those days. Dutch physicist Hendrik Lorentz acted as the intermediarycommunications-relay between Eddington and Einstein. The NY Times responded to the news with a whimsical headline:
Einstein was hailed as a 'new giant in world history' in the German press.
Einstein's calculations indicated that the universe is not static, but is expanding. At one stage, the universe was smaller, perhaps even a mere point. Einstein believed in a static universe, and added a cosmological constant to his equations in order to achieve a static universe. Urban legend has Einstein labeling the cosmological constant as his 'biggest blunder'. The model of an expanding universe was first proposed by Belgian priest and astrophysicist Georges Lemaître, who pioneered the Big Bang theory with his model of a 'primeval atom' or 'cosmic egg'. Edwin Hubble observing a redshift in light from distant galaxies, proved that space is expanding. In 1965, engineers Arno Penzias and Robert Woodrow Wilson accidentally discovered the cosmic microwave background radiation as they adjusted a radio telescope. Dr Dijkgraaf joked that the engineers had scooped the physicists, who were working on the problem of finding evidence for the Big Bang. The immediate post Big Bang period is known as First Light... and for people familiar with the old broadcast televisions, about 1% of TV static was due to radiation from the Big Bang.
In 2003, the WMAP satellite created an image of the cosmic microwave background radiation, an image refined by the Planck spacecraft. Dr Dijkgraaf likened the image of the 300,000 year old universe (from 13.8 billion years ago) to the universe's 'baby photo':
Dr Dijkgraaf noted that instruments cannot 'see' farther than the pointillist painting obtained by WMAP and Planck.
After the Big Bang, matter condensed, stars formed, and galaxies coalesced- the cosmic evolution started to be pieced together in the last one-hundred years, and a different history of the universe is being written. There are unknown facts, but the cosmologists know what they don't know. Dark matter is one mystery, it comprises five times the mass of baryonic matter... Dr Dijkgraaf stated that 'transparent matter' might have been a better name for the stuff. He likened dark matter to a Christmas tree, with the baryonic matter being the lights. Dark energy is the name proposed for the force which causes the increasing rate of expansion of the universe, the force in empty space which pushes the universe apart. Between dark matter and dark energy, 96% of the universe is 'missing', only 4% is known to us. Dr Dijkgraaf noted that other scientific fields work with a lot of 'dark knowledge'- for instance, paleontologists have to reconstruct evolutionary relationships with a fossil record that has huge gaps.
The topic of the lecture then shifted to black holes. There are two broad categories of black holes- stellar black holes are extinct stars which collapse under their own gravity while galactic black holes, also known as supermassive black holes, have a mass of millions or billions of stars. These galactic black holes spew vast radiotion plumes as gigantic, violent explosions constantly occur on their periphery. Stars in the galactic center revolve around the galactic black hole in elliptical orbits. A proposed Event Horizon Telescope would look into the center of the galaxy to obtain more information about the conditions around the black hole in the the galactic center.
Dr Dijkgraaf also noted the discovery of gravitational waves by the Laser Interferometer Gravitational Wave Observatory- this gravitational wave detector observed small waves which probably resulted from the interaction of binary black holes merging into one larger object. The LIGO is sensitive enough to measure the gravitic effects of an overhead cloud- Dr Dijkgraaf joked about 'lying on your back, feeling uplifted'.
A collision between two black holes detected in September 2015, which occurred over 1.3 billion years ago, resulted in the most violent explosion ever measured, a cataclysm which released more energy than that released by the entire visible universe.
Dr Dijkgraaf then shifted the topic of the lecture to particle physics and the Standard Model. He displayed a diagram of the years from concept to discovery:
Looking at the scant duration between theorizing about the existence of the muon and it's discovery, he noted that the joke concerning the discovery was, "Who ordered this?" The Higgs Boson took five decades to find. Peter Higgs, 86 years old when the discovery was made, stated that he was happy that the boson which bears his name was discovered during his lifetime. In contrast, it took a century between Einstein's proposal about gravitational waves and their discovery. Dr Dijkgraaf noted that science is a relay race, and that researches must pass the baton on to their successors.
Black holes took a longer time to discover- in the 18th Century, John Michell proposed the existence of stars with gravitational forces which were so powerful that light could not escape. In terms of mass, if the earth were compressed to the point where its gravitational field was so strong that light couldn't escape, it would be a mass two centimeters in diameter. In 1939, Robert J. Oppenheimer and Hartland Snyder described how a collapsing mass, such as a star collapsing under its own weight, could form a black hole. The black hole itself can be likened to a gravitational singularity, the boundaries of a black hole are known as the event horizon. An object within the event horizon is doomed. Dr Dijkgraaf noted that, if our sun collapsed into a black hole, it would have an event horizon three kilometers in diameter, which he jokingly described as 'Brooklyn sized'.
Time inside the event horizon flows differently, possibly stopping altogether. If the Big Bang represents time's beginning, black holes represent an end of time. The term black hole was coined by John Wheeler, who noted that black holes were a paradox- the laws of physics that we know break down. Nevertheless, the universe works, and we need to formulate a new theoretical framework. Originally, Einstein did not like the Big Bang and black holes, preferring a static universe, but he changed his mind as new evidence accumulated. Dr Dijkgraaf quipped, 'Sometimes, a theory is smarter than its discoverer.'
The topic then shifted to quantum theory- Dr Dijkgraaf posed the question, 'Why is every electron the same, does Nature have a perfect electron factory?' Richard Feynman recounted a telephone call from John Wheeler on this subject:
I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, "Feynman, I know why all electrons have the same charge and the same mass" "Why?" "Because, they are all the same electron!"
Dr Dijkgraaf asked us to consider an electron moving up and down through spacetime, making copies of itself and weaving a Big Knot- is the result many particles, or are they all the same? Richard Feynman drew diagrams representing the behavior of particles, showing the splitting and recombination of particles. The Feynman diagrams even graced the family van. In quantum mechanics, there is one edict- 'Everything which is allowed is obligatory, everything which can happen will happen.' The duplication of particles through quantum mechanics might form an explanation for dark energy.
The Planck length (×10-35 meter range) represents the size of the tiny 'pixels' which make up the universe, while the Hubble Scale (×1025 meter range) represents the size of the universe. About smack dab in the middle we find the scale at which life is organized (×10-5 meter range). The hot Big Bang was preceded by a period of rapid expansion of space known as the Cosmic Inflation Period. The classical density perturbations, the small disturbances at the quantum level, determined the large structure of the universe... the very small determines the structure of the very big. Dr Dijkgaard quipped that empty space is an exciting subject, and that more money should be dedicated to the study of Nothing.
Thermal energy, known as Hawking radiation is expected to be emitted from the event horizon of a black hole- two particles are thought to be produced at the event horizon, one which cannot escape and one of which is liberated due to quantum mechanics. Dr Dijkgraaf paused in the lecture to joke, 'What is the sound before the Big Bang? Oh, shit!" He noted that black holes are the most mysterious objects that we are aware of... they are the most complex objects, the objects which collect the most 'information'.
This formed Dr Dijkgraaf's shift into string theory and the role of black holes in string theory. He brought up such topics as AdS/CFT correspondence and the holographic principle, noting that a 'holographic universe' can be projected on black holes because of the physics that occurs on the event horizon. Space can warm and time can wrap. The visible universe can be explained by the interaction of light and matter, but the interactions are complicated and chaotic. The basic building blocks of the universe, though, are simple. Particle physicists see simplicity, but complexity can be seen in the interaction of molecules in a glass of water. Hydrodynamics and thermodynamics are emergent properties... the laws that regulate spacetime might emerge from something more simple, perhaps pure information acting as a matrix.
In the Q&A, some bastard in the audience asked the good doctor to comment on this recent model calling into question the role of dark energy. He responded that physics is an ever-changing field and that, ten years from now, the entire model might be different due to refinements and new observations, though it must be noted that Einstein was usually correct. In response to another question, Dr Dijkgraaf recounted an amusing family anecdote- his son asked him, 'What happened before the Big Bang?' He replied, 'That's what Daddy is working on.' The next day, his son asked, 'And?'
All in all, Dr Dijkgraaf delivered a great lecture- it was a combination of grand overview of physics and mind-bending string theory that I really need to read up on more. He is an engaging, informative lecturer who has a huge following online... if you can read Nederlandish, he has a lot of material. Once again, the Secret Science Club dished up a fantastic lecture- kudos to Dr Dijkgraaf, Dorian and Margaret, and the staff of the beautiful Bell House. I'll try to hunt down video links to illustrate these topics, but right now I have to run out for a second night of beer-drinking in a row. It's bar trivia night, and what better way to celebrate Useless Knowledge is there?
2 points:
ReplyDelete1.) The Higgs Boson did NOT take five decades to find. Once we had an accelerator that could generate sufficient energies, it only took four years. Before the design, funding and building of the LHC, we had no tool with which to 'look for' the Higgs.
2.) PLEASE do not waste your time, brain and curiosity on String Theory. You've got much better things to do. String theory is a kind of mathematical religious faith - utterly untestable, utterly unfalsifiable, and makes no testable predictions whatsoever. It's mathematical masturbation.
If you are thinking about digging into String Theory, first skip it all before QFT - basically everything called 'string theory' today is QFT and LQG. But first, read Peter Woit's seminal book 'Not Even Wrong' and Lee Smolin's brilliant 'The Trouble with Physics'.
Essentially, at this point String Theory is dead - people are still using the term to maintain some credibility for their past work, but it's evolving into other more scientific disciplines.
Worth noting is also the ongoing demise of SUSY. At the current LHC energies and luminosity, it's pretty clear that if there were superparticles out there, we would have found the lighter ones already. Some of the big bets that were made over ten years ago are being paid off this year...
The Higgs Boson did NOT take five decades to find. Once we had an accelerator that could generate sufficient energies, it only took four years. Before the design, funding and building of the LHC, we had no tool with which to 'look for' the Higgs.
ReplyDeleteI should clarify- five decades from theoretical basis to actual discovery.
If you are thinking about digging into String Theory, first skip it all before QFT - basically everything called 'string theory' today is QFT and LQG. But first, read Peter Woit's seminal book 'Not Even Wrong' and Lee Smolin's brilliant 'The Trouble with Physics'.
I'd pretty much written it off- I remember Neil Degrasse Tyson stating that it was an avenue of inquiry which didn't bear any fruit. Thanks for the recommended reading.