String Theory is probably the best candidate for a Theory of Everything, including the so far elusive Quantum Gravity. I have to say, that as viewer of the the matter from the outside, I’ve gone from a deep skepticism, mostly because of the lack of empirical validation, to believe that is the theory with most likely to thrive. The absence of reasonable alternatives, the internal consistency of the theory itself, and the historical background of other theories that emerged from mere theoretical considerations (eg the Standard Model), is behind of this personal evolution.
We’ll see, but meanwhile, this site does a good job of popularizing the theory itself, as well as an excellent review of almost all Theoretical Physics. From the page:
This site provides a brief and entertaining introduction to string theory for the general public. Topics include quantum gravity, string physics, current research, future prospects, history and news. Kindly supported by The Royal Society and Oxford Physics.
Dr Lise Meitner (1878-1968) was a Jewish Austrian-Swedish physicist known for her co-discovery of nuclear fission. Her passion for physics was inspired by her teacher at university, Ludwig Boltzmann, who taught her to see physics as “a battle for ultimate truth”, and in 1906 she became the second woman ever to graduate with a doctorate of physics from the University of Vienna. After moving to Berlin in 1907, she began to collaborate with Otto Hahn, a German chemist. Their partnership would last for 30 years and, by pooling their knowledge of physics and chemistry, they made huge breakthroughs in nuclear physics. In 1934, after Enrico Fermi split uranium, it fell to them to puzzle over the results. As a Jewish woman in Nazi Germany, Meitner was always in danger, but the Anschluss of 1938 forced her to flee under cover of darkness, breaking for the Dutch border. She travelled on to Stockholm, while Hahn and Fritz Strassmann continued to work in Berlin. The three later met secretly to plan their next experiments. Back in Berlin, Hahn and Strassmann bombarded uranium with neutrons and sent the results to Meitner; they had detected barium, a smaller nucleus. She and her nephew, Otto Frisch, correctly interpreted this as proof of nuclear fission, and recognised the potential for weaponisation. When asked to join the Manhattan Project, Meitner refused, declaring ‘I will have nothing to do with a bomb!’After downplaying Meitner’s contribution for years, Hahn won the 1944 Nobel Prize for Chemistry while Meitner was ignored; modern commentators call this one of the most glaring omissions of the 20th century, though this was somewhat rectified when Hahn, Meitner and Strassmann won the US Fermi Prize in 1966. Meitner eventually retired to Cambridge, England in 1960, where she lived until she died. The inscription on her headstone, composed by her nephew, reads “Lise Meitner: a physicist who never lost her humanity.”
We live in a wonderfully complex universe, and we are curious about it by nature. Time and again we have wondered—- why are we here? Where did we and the world come from? What is the world made of? It is our privilege to live in a time when enormous progress has been made towards finding some of the answers. String theory is our most recent attempt to answer the last (and part of the second) question.
So, what is the world made of? Ordinary matter is made of atoms, which are in turn made of just three basic components: electrons whirling around a nucleus composed of neutrons and protons. The electron is a truly fundamental particle (it is one of a family of particles known as leptons), but neutrons and protons are made of smaller particles, known as quarks. Quarks are, as far as we know, truly elementary.
Our current knowledge about the subatomic composition of the universe is summarized in what is known as the Standard Model of particle physics. It describes both the fundamental building blocks out of which the world is made, and the forces through which these blocks interact. There are twelve basic building blocks. Six of these are quarks—- they go by the interesting names of up, down, charm, strange, bottom and top. (A proton, for instance, is made of two up quarks and one down quark.) The other six are leptons—- these include the electron and its two heavier siblings, the muon and the tauon, as well as three neutrinos.
In the last few decades, string theory has emerged as the most promising candidate for a microscopic theory of gravity. And it is infinitely more ambitious than that: it attempts to provide a complete, unified, and consistent description of the fundamental structure of our universe. (For this reason it is sometimes, quite arrogantly, called a ‘Theory of Everything’).
Carl Sagan (1934–1996) was an astronomer, a skeptic, a science communicator and—to many—a poet. As a child he was fascinated with the stars, and this deep sense of wonder at the universe never abated all throughout his adult life. He studied at the University of Chicago, achieving his doctorate in astronomy and astrophysics by 1960, and over the next ten years, he held teaching and research posts at various universities and observatories. In 1970, he became director of Cornell University’s Laboratory for Planetary Studies and the David Duncan Professor of Astronomy and Space Sciences. At the same time, he played a leading role as a consultant at NASA, briefing the Apollo astronauts and being closely associated with unmanned planetary missions too, most notably the Mariner, Viking, Voyager, and Galileo expeditions. His research transformed planetary science, helping to solve mysteries such as the high temperatures of Venus, the seasonal changes of Mars and the reddish haze of Titan, and he also was a pioneer of the study of extraterrestrial life—but Carl is best known as a science communicator. In his award-winning books and his enormously popular 1980 TV series Cosmos, he captured the hearts and minds of millions with his easy charisma, his ability to explain difficult concepts, and his infectious wonder for the universe. His insights about our fragile world live on today as his legacy, and the way he continues to change the public’s perception of science is perhaps his greatest achievement—showing us that examining our universe using natural curiosity and the tools of science is a joyous, awe-inspiring endeavour. Happy birthday, Carl, and thank you for everything you’ve given us.
ercury has a curiously eccentric orbit that early astronomers had difficulty plotting. Although the Sun has the biggest gravitational influence on it, every other object in the Universe has an influence on it too according to Newton’s laws of gravitation. These are faint in comparison to the Sun’s enormous pull, but astronomers still have to factor them into calculations of Mercury’s motions. But in the mid 1800s, after painstaking calculation involving every known factor, French astronomer Urbain Jean Joseph Leverrier found that something was still unaccounted for. Neptune had just been discovered and had solved the problems with Uranus’s orbit, so rather than question Newton, Leverrier proposed in 1860 that there must be an object inside of Mercury’s orbit—a new planet that would account for irregularities. Leverrier called it Vulcan, but there was one problem: no one had ever observed it. Over the following decades, reports trickled in about various objects inside Mercury’s orbits, some perhaps small planets and others perhaps groups of asteroids. But the data didn’t match up, and no solid, consistent evidence could be provided. Controversy sprung up in the astronomical community, and yet, if Newton was correct, then there had to be another force acting on Mercury. In 1915, Einstein’s Theory of General Relativity explained it. It turns out that Newtonian gravity breaks down under extreme conditions, and relativity can step in to make corrections. Being so close to the enormous force of the Sun is certainly an extreme condition—basically, the Sun’s massive energy acts as the extra force on Mercury. When Einstein explained Mercury’s motions without the need for Vulcan, this shadow of a planet shrunk into non-existence—but it wasn’t a terrible hypothesis. Leverrier simply made the best inference he could with the available data.
Formulated in 1687, Newton’s Law of Universal Gravitation was a turning point in physic. While the legend of the apple falling on his head is an exaggeration of the truth, Newton did have a brilliant insight: that every object in the universe attracts every other object. The force of attraction between two objects depends on only two things: the mass of the objects, and the distance between them. So, more massive objects exert a stronger force, while more distant objects exert a weaker force. Newton was able to formulate a simple equation to describe this, pictured above: force is equal to Newton’s gravitational constant, multiplied by masses of the objects, then divided by the square of the distance between the objects. What’s remarkable is that the law truly is universal—not only can it predict how things move here on Earth, but it can also the movements of the moon, planets, stars and even galaxies millions of lightyears away. Newton believed that the movement of every object in our universe could be predicted, but we know now that while his theory generally holds true, it is not precise. Einstein’s theory of general relativity had to step in to fill the holes.
When the worlds of art and science collide, inspiration sometimes strikes in the sparks. Artist Roshan Houshmand creates a new perspective on the world of particle physics through her paintings, transforming physics into art. The paintings are based on the tracks of subatomic particles through bubble chambers, which are one of many kinds of detectors in particle accelerators designed to track particle movements. Bubble chambers are filled with superheated liquid, and the charged particles boil the liquid as they race through and leave a trail of bubbles behind. These compellingly beautiful patterns inspired Houshmand to create her series of ‘Event Paintings’. “I loved the sophisticated, simple playfulness of lines depicting charges, energies, speeds, mass and so much more,” Houshmand says. “There is something so pure and primal and universal about the movement of the trails and swirls and dancing lines against the black, which exist for less than a breath of time before they disappear.”
What happens to once-celebrated, now superseded theories?
Physicists are busy developing sophisticated theories around the existence of things that are impossible for us to see, perfecting mathematical models of the ‘beyond-visible’ worlds of the very large and distant (using Einstein’s theory of relativity) and the very small (using quantum mechanics).
Focusing on this realm of the intangible, I wanted to explore how abstract theoretical ideas can be visually represented. I also wanted to play with the notion that today’s cutting-edge theories may one day be seen as quaint and curious museum pieces: theoretical antiques or abstract junk.
Everything we can see and touch only makes up about 5% of the observable universe, and the rest is made up of 70% dark energy and 25% dark matter. Dark matter is a hypothetical form of matter that doesn’t emit or absorb light, heat or energy, so we can’t “see” it in normal ways—but we can detect its presence by its gravitational interactions with visible matter. In the 1930s, scientists observed that galaxies were rotating much faster than they should be. They should have been flung apart, because they didn’t seem to have enough matter to produce the gravitational pull needed to hold together, and so scientists inferred that there must be a large quantity of invisible mass. We can also detect it through the effect of gravitational lensing, which is the process of light being bent and distorted by matter. The image above shows the distribution of dark matter in the centre of galaxy cluster Abell 1689, 2.2 billion light-years from Earth. The light from galaxies behind Abell 1689 are distorted by dark matter within the cluster—it’s like looking at a shell on the sea floor, distorted by ripples on the surface. We don’t yet know what dark matter is made of, but there are two popular hypotheses: MACHOs (MAssive Compact Halo Objects), made of ordinary matter, or WIMPs (Weakly Interacting Massive Particles), an entirely new type of matter made up of exotic elementary particles.
In 2009, Nelly Ben Hayoun created an art installation under a London night-club that replicated a neutrino detector. It was based on the Super-Kamiokande neutrino observatory in Japan, which uses 11,000 golden photomultiplier tubes to register the light created when a neutrino meets an electron of pure water in their 45,000 tonne tank and creates a sonic boom. The installation, called Super K Sonic Booooum, consisted of a 22 metre long “river” through a tunnel lined with thousands of silver balloons (photomultiplier tubes). The public were invited to ride on a boat through the tunnel, accompanied by a physicist guide, to experience a recreation of the real Super-K interactions between neutrinos and electrons of extremely pure water, including sound and lighting effects to demonstrate a sonic boom. The artist’s aim was to engage non-scientists with particle physics, immersing them in a journey through the physics of our universe.
Black Holes are the densest, most massive singular objects in the universe—nothing can escape their pull, not even light. Theory holds that they are created when stars collapse under their own gravity, forming a point or a ring of infinite density—singularity. The nuclear fusion in a star’s core produces electromagnetic radiation that exerts outward pressure, balancing the enormous gravity of the star’s mass, but when the nuclear fuel is exhausted, stability cracks and gravity compresses the star inwards. If the star is sufficiently massive—theory suggests it must be three times as massive as our sun—then the gravitational force is strong enough to collapse the star into a black hole. Soon the radius of star shrinks to critical size, called the Schwarzchild radius or event horizon: the boundary beyond which nothing cannot escape, not even light, because the strength of the gravitational pull is too great. The radius for determining an object’s Schwarzchild radius is Rs=2GM/c^2, where M is the mass of the body, G is the universal constant of gravitation, and c is the speed of light—and anything that’s smaller than its Schwarzchild radius is a black hole. When a star reaches this radius, it starts to devour anything that comes too close—but what happens to material within the Scwarzchild radius, however, is a mystery. It collapses indefinitely to the point where our understanding of the laws of physics breaks down.