Unifying Quantum Mechanics and Relativity (v1.1)
The Physics of the very large and the physics of the very small are at loggerheads. Can both of these along with the standard Model and puzzles like dark matter and dark energy be unified into a theory of everything – the fundamental foundation on which all other higher knowledges rest? Is everything interconnected?
Science continues in its inexorable march to explain all the universe with one theory. This, and the current state towards this is the focus of this essay. But at this level, I can no longer explain anything at all in terms or analogies that falls within your experience. We can also start exploring the deep philosophical questions that arise from science, but that part must wait for another essay. In the birth of a universe, I talk about the universe starting from a singularity with a big bang with a plank density of energy. If all matter came from energy, where did this energy come from? If it came from something else, where did that come from? Something cannot come from nothing. To me the emergence of a single theory, if it happens, is a strong indication that there was infinite intelligence to creation. To me that is God. It is also the source of the energy of creation and the source of the total connectedness and harmony of everything. Everything is connected because there is one theory describing it. Everything is harmonious because physics theories are expressed mathematically, and the universe would be proven to be a mathematical system and that to me is harmony as well as order. Philosophers have also noticed that if the constants in physics were just a little bit different than they are, then life would not exist. There is a vanishingly low set of values for them that result in a viable universe for life. The universe is put together intelligently!! From a science perspective, a theory of everything will finally explain what was happening during the plank epoch immediately after the big bang, and what is happening at the center of a black hole. Science can go no further by its very nature. Beyond that is philosophy and theology.
All I can accept is that some phenomenon whose nature is unknown, and cannot be answered by the scientific method, was the source of spacetime and matter and energy, and imparted into the universe, assembly instructions in terms of the well governed laws of physics, laws of chemistry, and the laws of biology and evolution. These shaped the primordial universe to what it is today – one with great order, connectedness, harmony, and beauty, yet complexity and richness, and a world teeming with intelligent humans on earth and likely intelligent beings on other planets too. Are these laws the guiding instructions put into the primordial universe by God that resulted in such order, connectedness, harmony, and beauty, yet complexity and richness? Doesn’t that signal the existence of an intelligence and possibly purpose? I leave that up to you to judge. Einstein said “God does not play dice” when first presented with quantum mechanics. That implies he believed in God (actually Spinoza"s God) and likely saw beautiful and elegant equations like E=MC **2 as the handiwork of this intelligence. This conception of God does not invoke causality, space, or time. It does not require faith. It makes no statement on shape or form. But does attribute intelligence, and observes the universe is intelligently put together. It should pass scrutiny by philosophers.
Einstein said “I want to know how god created this world. I am not interested in this or that phenomenon, in the spectrum of this or that element. I want to know his thoughts. The rest are details.” Einstein's god may however be somewhat different than yours - he believed in Spinoza"s god. This blog is about God thoughts. It is about the BIG picture.
Crisp mathematical formulation in physics is very important.
- After Newton's equations of motion there was a lot of advancement in Physics.
- After Einstein's equations of special relativity there was a lot of advancement in Physics.
- After Einstein's equations of general relativity there was a lot of advancement in Physics.
- After Schrodinger and other's equations of quantum mechanics there was a lot of advancement in Physics.
- After Dirac's equations fusing quantum mechanics and special relativity there was a lot of advancement in Physics.
Two major steps towards unification in more recent decades deserve special mention to show how we got to where we are today. These are quantum electrodynamics and electroweak unification.
The first successful attempt to blend quantum mechanics with relativity occurred with quantum electrodynamics which is a modern theory of how particles interact with electric or magnetic force and replaces the older electric/magnetic field theory. In 1927, Dirac laid the foundation with the Dirac equation which successfully blended quantum mechanics with special relativity and incorporated the spin of the particle involved. A profound outcome is it predicted the existence of antimatter. For example, it showed that both electron and positron (antimatter of electron) existed. Positron was discovered in 1932. We now know that all forms of matter have antimatter. Matter and antimatter are essentially identical except for charge which is reversed. Matter and antimatter annihilate each other with a huge burst of energy (given by E = mc**2). Quantum electrodynamics describes the interaction between electrically charged particles and the mathematics is based on the Dirac equation. For interaction, they are constantly emitting and absorbing (exchanging) a bath of photons with different probabilities. The average of that all approaches the smooth classical picture of the electric and magnetic field. Richard Feynman was the key contributor and was one of the Nobel recipients in 1965 for this. Quantum chromodynamics used this as a model and was another major success and describes the interaction of quarks mediated by gluons.
An example of weak force is beta radiation in radioactivity. A major success was the unification of the weak force with the electromagnetic force. It was shown in 1968 that the Higgs field combined with 3 particles (which were later detected as W-, W+ and Z boson. Higgs boson that mediates the Higgs field was detected in 2012 which put in place the final piece) resulted in the forces of electromagnetism and the weak force. This is called the electroweak theory that showed both had a common origin. When this was finally verified, the two forces were unified as aspects of the same force.
What is dark matter? Astronomy showed that estimation of mass of galaxy’s observed was substantially less than the motion observed implied. The difference is called dark matter. Dark matter is estimated to have 5 times more mass than observed ordinary matter in the universe. Observation of a gravitational lensing effect in one instance showed the dark matter was centered at the centers of two colliding galaxies. There is a lot of speculation, but nothing proven. Could it be a new form of never seen matter? It is critical to solve this for a theory of everything and an army of scientists are working on this.
What is dark energy? We can measure the rate at which the universe is expanding by measuring the distance and speed of many galaxies. Distance can be measured by measuring the brightness of type A supernova in it. They have a known brightness. Speed can be measured by measuring the doppler shift of light from stars in that galaxy. In 1998, researchers observed that the expansion of the universe is accelerating. The gravity of the universe should have been slowing it down. Cosmological models showed that about 5 or 6 billion years ago, the expansion started speeding up. Ordinary matter and dark matter make up only 25 to 30% of the mass in the universe today. The rest is dark energy!! Dark energy is something unknown that pushes and accelerates the expansion. It is critical to solve this for a theory of everything.
Stephen Hawking discovered that black holes evaporate over time. As early as 1974 Hawking described how a black hole's mass and its temperature are inverse -- the smaller a black hole, the hotter it is, as Science Alert explains. This could only happen if a black hole emitted radiation, i.e., lost particles and mass. Such lost particles have come to be called Hawking radiation. But this is impossible, non-quantum physics would state, because a black hole's gravity is too strong. But it's not impossible if we take quantum mechanics into account, where a black hole loses particles non-locally, anywhere in the cosmos. This also concurs with the first law of thermodynamics -- energy can neither be created nor destroyed -- and brings us closer to a Theory of Everything.
Gravitational force is so incredibly weak compared to the electromagnetic force (the latter is 10 ** 36 stronger) that we will never be able to measure it in an atom with an experiment on its quantum nature. But it is necessary to explain what is happening at the center of a black hole, or when black holes merge when general relativity breaks down, or in the plank epoch in cosmology where general relativity breaks down. This explanation is necessary for a theory of everything. So, some new physics is needed – quantum gravity?. The development of this new physics is entirely a thought experiment. Cannot recrate the conditions inside a black hole or plank epoch in the lab.
There are four major theories that separately or together hold some promise towards a theory of everything and are being actively researched.
One theory is the MSSM (Minimal Supersymmetric Standard Model) which extends the standard model of particles and predicts new particles. But these predicted particles take incredible energy to produce in particle accelerators and have not yet been observed.
One theory predicts the existence of a graviton to mediate gravity. This has not yet been observed. If it exists, it is massless, electrically neutral, no color, with spin 2. It interacts with mass and energy and other gravitons and has extremely low energy. This would finally represent a particle for gravity that would further complete the standard table.
One theory is superstrings. This theorizes minute strings or hoops that vibrate in three space, one time and 6 more dimensions. The extra 6 dimensions are small and constrained (example a thick wire with a circumference, where one dimension is going around the wire, or a point with a knot in a hoop). Each mode of vibration corresponds to a particle in the standard model. This, if successful, would collapse all the particles in the standard model to a common foundation and merge relativity and quantum mechanics which further advances towards a theory of everything. I have written a separate essay on superstring theory for more details.
Another theory is loop quantum gravity. Loop quantum gravity (LQG) is a theory of quantum gravity, which aims to merge quantum mechanics and general relativity, incorporating matter of the Standard Model into the framework established for the pure quantum gravity case. It is an attempt to develop a quantum theory of gravity based directly on Einstein's geometric formulation rather than the treatment of gravity as a force. As a theory LQG postulates that the structure of space and time is composed of finite loops woven into an extremely fine fabric or network. These networks of loops are called spin networks. The evolution of a spin network, or spin foam, has a scale above the order of a Plank Length, approximately 10−35 meters, and smaller scales are meaningless. Consequently, not just matter, but space itself, prefers an atomic structure. LQG is formally background independent. Meaning the equations of LQG are not embedded in, or dependent on, space and time (except for its invariant topology). Instead, they are expected to give rise to space and time at distances which are 10 times the Plank Length.
Superstring theory currently focuses on particles and forces in space-time (background dependent), while loop quantum gravity currently quantizes space-time itself. There is a third recent proposal that introduces stochasticity into space time instead of quantizing it. I wrote an essay on it.
The Nuance: While perturbative string theory started as background-dependent (proposing strings moving through a pre-existing spacetime grid), modern developments like M-Theory and the AdS/CFT correspondence (holographic principle) have shown that spacetime can actually emerge from the quantum entanglement of boundaries. String theory is actively evolving to become just as background-independent as Loop Quantum Gravity.
Current Context: Data from the Large Hadron Collider (LHC) and subsequent upgrades have severely constrained the simplest models of Supersymmetry (SUSY). Because we haven't found these "partner particles" at the expected energy scales, many physicists have shifted focus. String theory, too, faces a prominent "crisis of empiricism" because it operates at the Planck scale, making direct experimental verification virtually impossible with modern technology.
We still have a way to go for a theory of everything and everything described by a single equation, but I am confident we will eventually get there. I am just as confident as a religious figure is confident there is God with the same amount of empirical evidence!! Another essay dwells into the opportunities and challenges of superstring theory.
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