Philosophical questions arising out of physics (v1.0)

 

The Greeks tied theology, science, and philosophy together. But later around the time of Newton, (and especially after the work of Bertrand Russell) physics became not an explanation of nature (which was philosophy and theology), but a mathematically accurate description of natural phenomenon and the interconnectedness of natural phenomenon. It became a self-contained discipline, borrowing tool of logic and math (which are parts of philosophy) to accurate describe reality. When two or more natural phenomenon was connected branches of physics merged. When a description of a natural phenomenon raised new questions, a branch of physics was spawned off. For example, mechanics, gravity, and thermodynamics merged as Newton outlined the laws of gravity and motion and showed gravitation motion and mechanical motion are the same and Maxwell showed that thermodynamics was due to motion of molecules. Optics, Electricity and Magnetism merged when Maxwell showed the relationship between electricity and magnetism which can mutually interact and create waves and showed that light was an electromagnetic wave. Electro-magnetism and motion merged when Einstein tied the two together and produced spacetime and the speed of light barrier for motion. And quantum mechanics merged matter with waves including electromagnetism. Discovery that matter consists of enormous number of atoms or molecules spun off statistical mechanics.

But Einstein triggered a revolution in philosophy. He completely reinterpreted mass, energy, space, time, motion, and gravity and that has deep philosophical implications and the branch of philosophy called philosophy of physics was born. About then, the philosopher Hempel formally described when physics “explains” something, and that physics should not only describe but explain where possible. Kepler’s laws are explained by the more complex and accurate Newtons laws and Newtons laws are explained by the more complex and accurate Einstein’s laws. But what explains Einstein’s laws? Einstein’s laws are a more accurate description of nature but is less of an explanation. There is tension between accurate truth and explanation.

Philosophy now mainly consists of logic/math, epistemology (study of knowledge), Metaphysics (study of reality), and Axiology (ethics, and aesthetics). This blog will not really go into any aspect of ethics and physics. But things like symmetry, and simplicity, and Occam’s razor which often drive physics touches on aesthetics, but I will not go there further. Math is completely abstract. However all too often physicists studying a phenomenon find a mathematical system someone has already created available coincidently so they can proceed and use it as the tool. Why is math so useful and all-pervading in physics? That is an interesting philosophical question, but I will not dwell on that. I will now only focus on key philosophical questions that sprung out of physics in the branch of philosophy of physics in the modern era and only a few topics to keep it short. I will focus only on spacetime, gravity and quantum mechanics.

SPACETIME AND GRAVITY:

First, I shall address space. Is space real? Newton was also a philosopher and argued space was real and absolute (and so was time). His contemporary Leibniz (coinventor of calculus with Newton and a philosopher too) and later the philosopher Mach disagreed. What’s left when you take all matter and energy out of space? Either something or nothing. Newton believed the former. Leibnitz the latter. To Leibnitz, space was relative. Einstein was strongly influenced by Leibnitz and Mach’s arguments that space was not absolute and real but relative. Special relativity buttressed Leibnitz and Mach’s view and in it, space is not a real and absolute thing. Spacetime is explicable as a dynamically evolving network of relations.

Is gravity real? Newton argued gravity was real just like space. Einstein in the general theory went the other way that the movement of an object that is moving due to gravity is the same as any other motion, so gravity is not real but a geometry of space. Space is influenced by matter/energy in it and influences matter/energy back in return. The relationship is geometrical. Newton saw space as an infinitely long and wide and deep uniform thing with gravity a field in it while Einstein saw space more like a trampoline that warps due to objects/energy on it that in-turn affects other objects. But in the general theory which is a generalization of the special theory that also accounts for gravity, space has curvature which is a property. Only things have property. So, is space real after all? That is a contradiction from the assertion that space is relative in the special theory. How to resolve this philosophical dilemma?

Poincare and Reichenbach showed that physics presupposes a geometry and geometry presupposes a physics. The way to resolve is pick one. If you pick a geometry, then you empirically develop the physics. Similarly, the other way around too. It is a convention. They pointed out that Newton thought gravity was a field in flat space while Einstein thought gravity was a curvature of space. Curved space can be rewritten to be expressed as a field in flat space. Since the predictions of both is the same, they are the same, just a difference on how we choose to describe it. A difference in language. So, there is no property, so there is no reason to say space or gravity is real, and Mach/Einstein reign supreme.

There are three philosophical aspects to time. The direction of time. The origin of time. Is travel back in time possible? Newton thought time was a thing unto itself, and was absolute, that flows unidirectionally in one direction and carries everything with it. However, his laws show time symmetry – it works for negative time flow just as well as positive time flow. Same for Einstein’s laws. Einstein also showed that time was relative and merged with space and we need to talk about a four-dimensional spacetime. But no known instances of reverse time flow is known. Does that mean Newtons and Einstein’s laws are wrong?

Reichenbach points out that thermodynamics is not symmetric. Entropy increases (Second law of thermodynamics). The second law of thermodynamics does not say disorder will always increase, but instead that the number of possible states increase. Reichenbach argued that to go towards less disorder requires some action and is therefore tied to causality which has a definite time arrow direction. But the universe is currently expanding and could contract in the future, where the number of states decrease and therefore entropy decrease. So, we cannot hang our hat for unidirectional time on entropy.

Gödel showed that with relativity, with the right distribution of mass and energy, and a fast enough moving electron, an electron can collide with an earlier incarnation of itself, and relativity does not preclude time travel. But time trave allows changing the direction of the causal arrow. I can go back and kill my own grandfather before he was married, so I don’t exist and cannot go back. This is a contradiction.

First, the laws allowing time travel is different from saying it is technically possible or practical to do so. In the contradiction above, there is a causal loop. There could be a million reasons that can intervene to prevent me from killing my grandfather. The causal loop could be consistent. For example, in my grandfather’s history, there might be a case of someone taking a potshot at him and missing. That someone could turn out to be his grandson who went back in time. This is a consistent causal loop. So, a causal loop by itself does not negate the possibility of time travel. But an inconsistent or contradictory causal loop is not possible.

There is now a preponderance of evidence that the universe was formed with a big bang when spacetime began, and the universe itself is expanding and even the expansion is accelerating. The most telling evidence isthe microwave background radiation which is everywhere and is the echoes of the explosion. So about 13.8 billion years ago there was no spacetime and the big bang occurred from something akin to a singularity and the universe has been expanding since. The philosophical enigma is how did that something like a singularity (or point from which expansion occurred) happen to be and what caused the big bang and what was before it? The first interpretation by the pope was God created it. Grunbaum argues that a theological interpretation of these questions makes one of three logical mistakes.

1. The assumption that because everything is caused in spacetime, there must be a cause to the universe. Causality applies to spacetime. What applies before spacetime?

2. The question what happened before the big bang does not apply because time did not exist then. What applies then?

3. The cause of the big bang is beyond the scope of science and reason. It is also beyond faith because you can only have faith in a proposition you can understand.

In the promise of a theory of everything essay, I proposition a concept of a god as the source of the energy. But I make no mention of causality or time or space. I also don’t ask for faith but make a case based on observed order, beauty, harmony and connectedness and therefore postulated that the universe is intelligently put together and called that intelligence “god”. So, I think the above argument by Grunbaum does not negate my argument.

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.

QUANTUM MECHANICS:

There was general acceptance that things were deterministic, and matter properties and energy were continuous. Determinism states that if you know the state of something, then its future evolution is fixed. Quantum mechanics shattered this belief system. Equations like Heisenberg’s uncertainty principle says (for pairs of properties like momentum and position), the more exactly we know one, the less exactly we know the other) resulted in the world of the subatomic and radiation becoming probabilistic. The Heisenberg’s principle interestingly is about what is (metaphysical), not about what we can know (epistemological)!! Before measurement it really does not have a position. It is in a superposed state of many positions!! Also, it established that things like energy, momentum, and angular momentum come in packets. Also matter (at least measurably at the subatomic level) and radiation are BOTH a wave and a particle. How can that be!!

The Schrodinger wave equation is the key equation in quantum mechanics. In Newtonian mechanics, the state function are the laws of motion, and the state variable are mass, velocity, acceleration, etc. In quantum mechanics, the state function is the Schrodinger wave equation, and the state variable is the sum of every possible value the property could have if measured, multiplied by the probability of that value. Measurement gives a single value for the property, but it is in a superposed state with respect to the other property. Its value is indeterminate. It is weird!!

From a philosophical perspective this undermines the fundamental principles of logic itself that a statement is either true or false. To resolve this Von Neumann (whose early computer architecture is still used today) produced three valued logics. A statement can be true, false, or indeterminate.

Particles and waves are not only different things but diverse types of things. So, de Broglie equation relating mass of matter to frequency of waves shook conventional wisdom (mass * speed of light **2 = planks constant * frequency). So light and matter are both particles and waves. If we look (a measurement) it acts like a particle. If not, it acts like a wave. Same for electrons, atoms, or molecules. How can that be? It seems to violate causation. Bregmann argues that quantum mechanics are really a set of rules governing measurement. Measurement is a result of observation. The Schrodinger wave equation does give us the correct measurements statistically every time. Causation is a metaphysical notion that is only required if we are trying to see the invisible forces underneath the observed reality. But if you jettison the metaphysics, and only focus on observation, then there is no concern. This posed a problem for philosophers who believe in realism – an example follower is Einstein. Einstein felt quantum mechanics was incomplete and never really accepted it. But it is one of the most successful theories ever. No measurement has ever failed quantum mechanics!!

There are some exotic philosophical interpretations of superposition and the collapse of the wave function on observation and quantum entanglement but that is beyond our scope.