Physics & Philosophy

Illustrations – Gunjan Joshi

Assuring Reality

When one gently proffers “Physics” as an answer to Philosophers’ gnarly conundrums, one is often met with a ‘stop-right-there’ stare. Upon querying further, one is told that Physics does not get at the ‘essence’, the Kantian ‘noumenon‘ [12] – the thing itself. Plainly put, how do you know you aren’t in the Matrix? You don’t. Hence, what is real is unknown and Physics shall never lay its finger upon the noumenon. I see a simple resolution of this matter. If you cannot distinguish Matrix from reality, then the two are one and the same. There is no difference! How could there be? Hence what surrounds you is your reality, and Physics does get at it. Period.

Multitudes of philosophers may groan at such reasoning. For them, an even looser approach exists. Cede, for the moment, that Physics does not indeed get at anything. Then why favour Physics? On the simple principle that it works. Out of all the theories mankind has formulated to explain our world, Physics has been the most successful. The moment you have a more successful approach, I shall cleave to it and cast aside Physics. But for now, Physics best explains our world.

Ultimate Cause

The reason yours truly ever got into Physics was in pursuit of ‘Why?’. From the pedestrian ninth grade ‘Why is the sky blue?’ to the utterly profound ‘Why do we exist?’. The recursive ‘Whys’ spiralling, self-folding, domino like, into Physics. But at its heart Physics as we know it is the particles of the Standard Model [1] and the four fundamental forces that bridge them. Why those particles? Why those forces? Why four dimensions? Do these questions even have answers. Doubtless you must’ve heard and envisioned reality analogized to the layers of an onion. We peel back each layer only to find another underneath. Perhaps there is no ultimate answer? Then how are we to reconcile that with our desire for certainty and explanation? Do we turn to religion for ultimate answers? Or can we proffer, can we dangle a few tantalizing possibilities of our own. To show that all is not lost, ultimate answers there be might.

Turtles all the way down. Credit: Gunjan Joshi.

As of this day, as you read this, the best ultimate cause Science has identified is our good ‘ol Big Bang [2]. I admit it is a deeply satisfying ultimate cause as far as ultimate causes go. Things blew up – they really really blew up. Imagining it is fun. The universe expanded at a dizzying rate. Baryons and protons, quarks and gluons rubbed shoulders with each other. Relativity and quantum mechanics nodded amicably. It was great. But philosophers, as they are wont to do, threw a spanner in the works. Why the Big Bang? What caused that huh? And no one has any idea.

Rack your brains. Cogitate. What do you think? How did we get here – inflation [3]. What’s the opposite of inflation – deflation? Right. What if deflationary processes set in. The universe would contract – it would snap back. Like a rubber band stretched too far. Just as the strong force acts on the order of femtometers 10-15 meters) why couldn’t we have a force that acts on the order of 1015 meters? And is simply undetectable below that threshold. The size of the universe is 4.34×1034 meters. Thus our dear hidden force would have to act at larger length scales than that. And if it ever caused a snapback, we’d get a Big Crunch [4]! And then presumably another Big Bang. This would go on for ever! The universe would simply yo-yo back and forth.

Unfortunately for us, this only kicks the proverbial can down the road. Our niggling dissatisfaction, that lack of a first cause, continues to prod us onwards. Now, inductively, if we are to drive to a cause, then we ask for a cause for that cause. There is no end! There are turtles all the way down [11]! Inductive reasoning waggles its long, bony finger at us. ‘A dead end!’ it says. There is nothing here for you. Clearly, angling for a cause is the problem. Then what? Remove the problem! What if there was no cause. Is that so far outside conception. There is only one possibility then left, as far as I can see. Which is – our universe arose randomly [5]. Out of nothing. We posit nothing! And randomness. It is difficult to see how one could get more fundamental than this. Nothingness requires the absence of a cause. As does randomness. The actual mechanism could be completely outside of our understanding. Am I positing magic? No, just as a particle and anti-particle can be produced randomly [6] out of nothing, our universe could be produced through a random perturbation in nothing. A flap in the nothingness. This is not deeply satiating, only superficially so, since our first cause is a hydra of a question. And as we peel back a layer, it rears back another question. Why can’t nothingness stay nothing? Why must there be a fluctuation? Strictly speaking, if we posit nothing, posit no rules, then there is nothing to say that a particle anti-particle pair cannot form. And such an event can happen should we start with nothing. Perhaps further resolution of fundamental laws shall bring the metaphysical to the physical but at this point, such is our best.

Time Emergent

TIME. A subject philosophers cannot get enough of. They will wrap their heads around it till it vexes and strains them. What is time? How do you measure time? You look at the pixels on the bottom right of the screen. The digits tick upwards. A change indicates time passed. How do those digits tick? Digital circuits in your computer switch on and off. Again that switching indicates time passed. Thus, time is simple. For time to pass, you need a change. If every single particle stayed static, time would not pass. A gedanken experience to reinforce this! Say you’re playing football with friends. At some point, it so happens all of you are in the very same positions as you were first were in. Now, to someone who just checked back, there is no obvious change. Thus, for them, there is simply no way to tell that time passed. A more fundamental gedanken experiment which made it crystal clear for me. The decay of a radioactive particle. It is completely random, and is proportional to the amount of time that has passed. The obvious conclusion that the passage of time ‘is forcing’ the particle to decay, there being no other possible cause. But, look at it the other way. There are probabilistic quantum mechanical phenomena occurring that eventually tip the particle into decay. And that decay is a change. And that change let’s you measure time.

If you prefer a more quotidian example, is time making a pendulum swing, or is time resulting from the swinging of the pendulum? The descriptions are equivalent. However, if you posit time as fundamental, you are positing an unknown, mysterious force. Instead, if you accept time as emergent from the change of state of particles, you have a cogent theory for time.

The next arrow in the naysayers’ quiver is that of the arrow of time. Why does time move in one direction? Specifically, why do things break and never reform, why do shoelaces untie themselves but never tie themselves. The answer is deceptively simple. There are umpteen ways in which your shoelaces can untie themselves — but only one in which they can tie themselves. It is simply probability. More broadly, there are infinitely more ways of going from order to disorder than from disorder to order. The probability of going from order to disorder is always higher. Hence, we possess an arrow of time. Phenomena tend towards an increase in disorder. Things tend to breakdown than build-up.

Uncertainty Principle

The eponymous Heisenberg Uncertainty Principle [7] essentially states that you cannot know a particle’s position and velocity simultaneously. This is fundamental and has nothing to do with how good your measurement is. I offer a simplistic explanation for this, which I should clarify is pure speculation. You want to know how fast your car is going. Ask yourself if an instantaneous measurement would do that job. And the answer is a vehement ‘no’. In order to measure speed, a car has to actually move. You measure the time elapsed for it to go from A to B, and get speed = distance/time. Fundamentally, in order to measure movement, you need to have movement. And the larger the distance between A & B is, the more accurate your measurement.

Can you reason to the Uncertainty Principle from here? Think about it – take a minute. If a thing must move to measure velocity, then obviously you cannot know its position! Because it was moving during the measurement! And the further it moves, the more accurate your velocity measurement! And the less accurate your position measurement becomes. This theoretical reasoning exactly mirrors the uncertainty principle wherein the accuracy of velocity and position measurements are inversely related by the relation, (uncertainty in position) x (uncertainty in velocity) >= planck’s constant/(2*pi). The crux of it is that position and velocity are inextricably tied up, and to measure one necessarily makes the other fuzzy. But again, this section is speculation on my part.

Quantum Mechanics

Methinks a quick & dirty survey of QM is in order. “Quantum” means everything is discrete. The light emitted from this screen hitting your retina is not a continuous wave, but a stream of photons. Thus there could be a 1000 photons or a 1001 photons, but not 1000.534 photons. There’s no chopping those photons up! Now I wish things were that simple. Because you go “okay they coming in discrete units, but what are they”? Indeed what is a particle? And here things get murky. You see, when boffins figure out what tricks a particle is up to, they don’t actually solve for the particle. They solve for the particle’s wavefunction. Think of the wavefunction as a fog spreading from the particle in all directions, feeling out where the particle can and can’t be. Then poke the particle, say shine light on it, use a magnetic field – whatever. Essentially, interact with it. And you will find the particle at a particular spot. There will be no trace of this ‘wavefunction’. The wavefunction can never be measured. What is it then? It is related to the chance of finding the particle at a point. The wavefunction gives us the space over which the particle could be found, and the associated chance of finding it. But when we try and find the particle, we will find it as only one point. Is the wavefunction a real thing? No one knows for sure. What we do know is that it perfectly predicts the outcome of experiments.

In short, when you measure a particle repeatedly you find it distributed in accordance with its wavefunction. But you can never measure the wavefunction, only the particle. Thus, the wavefunction does mean something, but what? No one knows.

The Measurement Problem

“Wave-Particle Duality”, “Wavefunction collapse”, “Measurements”. You may have heard these terms being casually bandied about. What the what do they mean? The ‘measurement problem’ refers precisely to our discussion above. When we measure a particle, the wavefunction disappears and we find the particle. How does this happen? Is there a wavefunction? And the measurement itself. What constitutes a measurement? What is and what isn’t sufficient to collapse a wavefunction into a particle? Is there some sort of threshold for a measurement to occur? These questions are yet to be resolved.

Entanglement

A phenomenon which makes the case curiouser and curiouser is entanglement. It is possible to ‘entangle’ multiple particles such that their properties are correlated. Thus, measuring the property of one particle means you instantly know the other particle’s property. What is amazing is that measuring one particle instantly causes the other particle to assume the corresponding state. Thus if two photons are entangled, and you measure one photons’s polarization to be ‘up’, the other one instantly switches to the opposite polarization. Thus, not only is communication between the two photons faster than light, it is instantaneous. Explain that! Ha.

The Double Slit Experiment

The Double Slit experiment [8] is everyone’s favourite befuddler. Hokay, you have two slits in a screen close to each other and a wall behind it. You send light through the two slits and you get a banded interference pattern on the other side. For diagrams and a more detailed explanation click on the link. Now the QM explanation is not that light goes through each slit separately and interferes with the light from the other slit. No. It is that light goes through both slits simultaneously and interferes with itself. Your brain recoils from this. Through both slits simultaneously? Why, that makes no sense at all. This is how I think of it. It’s speculation but it makes sense to me.

What information do you have? You know photons moved towards the slits and you know they hit the wall on the other side. That is it. Think of it this way. Say I tell you I went from LA to San Francisco. Now I probably took Freeway 5. But I could’ve taken the 1, the 101 or the 99. Heck I could’ve flown to Alabama and then to SF. Or passed by Jupiter on my way there. You have no idea. From your epistemological perspective, you cannot make any sort of claim as to the route I took. Thus, according to you, it only makes sense to consider I took all routes with some weightage of probability as to the routes.

This is exactly what happens in a Double Slit experiment. You do not know what happened in between the photon leaving the light source and hitting the wall. Then, is not the only reasonable take on this that the light went through both slits, since you cannot say which slit it went through? More importantly, information as to which slit a photon went through does not exist anywhere, accessible or inaccessible. I cannot emphasize this enough. Information as to the route I took to SF from LA will exist somewhere. Someone saw me on the freeway, or I was measured in a physical sense by sunlight interacting with me – whatever. There was some effect on the world. But here there is no way to say a photon went through only one slit at all. The only possible physical phenomenon that can occur is for light to go through both slits and interfere with itself. Another way of putting it is thus. But first, an Einstein quote. “We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.” So, do you think the moon is there if you aren’t looking at it? Your gut instinct is to say yes, ofcourse! Personally, that doesn’t make sense. If you aren’t looking at the moon, you have absolutely no way of saying where it is. It could be anywhere. In the Andromeda galaxy for all you know. You do not have enough information to answer. As with the double slit, you do not have information to answer which slit the photon went through, hence it went through both.

Schrodinger’s Cat

Schrodinger’s Cat Lives! Credit: Gunjan Joshi.

With the rise of the cat in modern culture, Schrodinger’s Cat [9] is fast supplanting the double slit (or has supplanted) as the favourite befuddler. Legions of cat owners desire to know if their cat is dead or alive. Very simply, you put a cat in a box with a radioactive particle. If the particle decays, the cat dies via some complicated mechanism. Since the particle probabilistically decays, the cat is probably dead or probably alive. This, to our venerable Schrodinger, is ridiculous. It makes perfect sense to me. Unfortunately, it affects your sensibilities and you reject it as ridiculous. But ofcourse if you do not have information to make a determination either way, then your only choice is to take the cat as dead and alive from your perspective. In physics jargon, the cat is in a superposition of being dead and alive.

Kochen-Specker Theorem

When you have a name like that, you know the theory[13] is going to be intense. From my understanding of the theory, it is more a statement on quantum mechanics itself than a statement on reality. The theory sets limits on your interpretation of quantum mechanics. In QM you measure something and end up with a measurement. The KS theorem says the quantum state corresponding to the measurement did not have a defined, actual value prior to the measurement. My conclusion from is that if a thing is not interacting (i.e. not being measured) its state becomes undefined. Thus, things need to be measured to have definite values.

Current Approach

Since these are questions that physicists do not have clear answers to, the most common approach physicists take is the ‘shut up and calculate’ approach, where philosophical issues are brushed aside as hopelessly vexing and thus fruitless to pursue.

Are Space & Time Discrete?

Huge philosophical question. Take a crack at Zeno’s Paradoxes [10] for example. I’m going to stick my neck out and say space is certainly discrete. And if you followed my argument that time is emergent from space, then time is similarly discrete. My reasoning is simple. Space is either discrete or analogue. Well then, define analogue for me. You will say something like ‘not discrete’. That is it! You do not have a conception of analogue! Because it makes no sense. A thing cannot be analogue. This universe is discrete, and everything in it is discrete. This is apparent in that we must define analogue-ness in terms of discreteness. I am willing to wager a small sum of money that space is indeed discrete. Indeed that everything in this universe is discrete. This is why mathematics is so effective. Math is built upon this very idea. That things are discrete and there are rules between them. So comes forth the structure of mathematics, and its effectiveness in describing the world around us.

Caveats

And that completes the Physics & Philosophy discussion. I wish to add a caveat here that my knowledge of Physics is about intermediate. I certainly do not know much of Relativity or Particle Physics. There could be mistakes here, there probably are, but I still think this provides excellent food for thought.

References

  1. http://en.wikipedia.org/wiki/Standard_Model
  2. http://en.wikipedia.org/wiki/Big_Bang
  3. http://en.wikipedia.org/wiki/Big_Bang
  4. http://en.wikipedia.org/wiki/Big_Crunch
  5. http://en.wikipedia.org/wiki/Boltzmann_brain
  6. http://en.wikipedia.org/wiki/Quantum_fluctuation
  7. http://hyperphysics.phy-astr.gsu.edu/hbase/uncer.html
  8. http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec13.html
  9. http://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat
  10. http://en.wikipedia.org/wiki/Zeno%27s_paradoxes
  11. http://en.wikipedia.org/wiki/Turtles_all_the_way_down
  12. http://en.wikipedia.org/wiki/Noumenon
  13. plato.stanford.edu/entries/kochen-specker/

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