(See Part 1 and Part 2. Also I am going to suspend the limit of three comments per post for this series of posts because it is a topic that benefits from back and forth discussions.)
Einstein was a firm believer in what we call objective reality, the idea that objects have properties that exist independently of, and prior to, any observer measuring them. As fellow physicist Pascual Jordan recalled, “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.” In this case Einstein, who is so often associated with turning our views of space and time upside down, was firmly on the side of the ordinary person in the street in believing in objective reality. He felt that the nature of objective reality required the particle to be spin up or spin down even before any measurement on it and so a complete theory should give solutions that contain that information. The fact that quantum mechanics stopped short of doing so meant, he felt, not that it was wrong but that it must be incomplete, the stepping stone to a more comprehensive and better theory that encompasses it.
But after more than a century, no such theory has emerged and many (probably the overwhelming majority) of physicists have come to accept that the lack of more information than is provided by quantum mechanics is not a failure of the theory but is because there is no more information to be had. In short, there is no objective reality, at least in the quantum world. The theory is indeed telling us everything that we can know and so is complete.
As a result of the experimental success of quantum mechanics, most physicists now feel that the classical Newtonian laws of motion are also not fundamental but merely approximations that are forced on us due to the technical difficulty in applying the laws of quantum mechanics to large objects that are made up of vast numbers of elementary particles. Even fairly small molecules, which we would consider microscopic, can be too large to treat quantum mechanically. So we treat the separation of knowledge into classical (macroscopic) and quantum (microscopic) worlds as due to our inability to apply the laws of quantum physics everywhere.
So we now have two worlds, the microscopic and macroscopic, behaving in very different ways according to different laws. That is, of course, a highly unsatisfactory state of affairs. There is just one world and so we should have just one theory that governs all aspects of it at all sizes.
While applying quantum physics to large objects is very difficult, there have been some major successes in combining classical laws of physics with quantum mechanics. The laws of electromagnetism represented by Maxwell’s equations are classical and believed to be fundamental but we have been able to integrate it into quantum physics to create the theory of quantum electrodynamics. The laws of special relativity are also classical and considered fundamental but we have been able to combine them with quantum physics to give us relativistic quantum mechanics and quantum field theory. But the world of general relativity, also considered classical and fundamental, is a nut that has been too tough to crack. There are people working hard to create theories of quantum gravity but without success so far. String theory is one such attempt that was in vogue at one time but seems to have faded due to its progress being stalled and lacking evidentiary support due to its inability to make predictions that can be tested. But while we have been able to adapt at least come classical laws to the quantum world, those new forms of laws are still only usable when applied to small entities. We do not know how to use them for large systems made up of many smaller ones so we still face that major problem.
While we talk glibly of the macroscopic and microscopic worlds, some readers may have already wondered about where the separation between the two world lies. What size represents the boundary between the two worlds? The fact is that there is no clear dividing line. What scientists have tried to do is slowly expand the reach of the quantum world into the classical world, no mean task. Over time, scientists have been able to find larger and larger entities that obey the laws of quantum mechanics. This year’s Nobel prize for physics, for example, was awarded to three scientists who expanded the size even further. As the press release states:
A major question in physics is the maximum size of a system that can demonstrate quantum mechanical effects. This year’s Nobel Prize laureates conducted experiments with an electrical circuit in which they demonstrated both quantum mechanical tunnelling and quantised energy levels in a system big enough to be held in the hand.
Quantum mechanics allows a particle to move straight through a barrier, using a process called tunnelling. As soon as large numbers of particles are involved, quantum mechanical effects usually become insignificant. The laureates’ experiments demonstrated that quantum mechanical properties can be made concrete on a macroscopic scale.
In 1984 and 1985, John Clarke, Michel H. Devoret and John M. Martinis conducted a series of experiments with an electronic circuit built of superconductors, components that can conduct a current with no electrical resistance. In the circuit, the superconducting components were separated by a thin layer of non-conductive material, a setup known as a Josephson junction. By refining and measuring all the various properties of their circuit, they were able to control and explore the phenomena that arose when they passed a current through it. Together, the charged particles moving through the superconductor comprised a system that behaved as if they were a single particle that filled the entire circuit.
This macroscopic particle-like system is initially in a state in which current flows without any voltage. The system is trapped in this state, as if behind a barrier that it cannot cross. In the experiment the system shows its quantum character by managing to escape the zero-voltage state through tunnelling. The system’s changed state is detected through the appearance of a voltage.
The laureates could also demonstrate that the system behaves in the manner predicted by quantum mechanics – it is quantised, meaning that it only absorbs or emits specific amounts of energy.
(A brief digression on tunneling. Imagine a track which contains a hump along it. If you roll a ball along the track, whether it manages to clear the hump or not depends upon its initial energy. If its initial energy is larger than the potential energy needed to reach the top of the hump, it will always clear the hump. If less, it will never do so. Instead it will rise up part way, stop, and roll back down. But if the system is quantum mechanical, then there is a non-zero probability of the ball getting to the other side of the hump even if its energy is less than the energy that is classically required. We say that the ball ‘tunneled’ through the barrier, as if it bored a hole through it. This is, of course, also a metaphor. We don’t know exactly how it got to the other side. All we know is that we sometimes find it there where it should not be classically.)
While the effort goes on to try and expand the size of the entities that we can treat quantum mechanically, there is one place where the macroscopic and microscopic worlds collide that causes major conceptual difficulties and and that will be looked at in the next post.
Next: When microscopic and macroscopic worlds unavoidably collide
I can understand that there is no objective reality as we perceive it but saying that the existence of something depends on us observing it (no matter how the observation is made and the experiment conceived, it still depends on a human having the information at some point) looks to me like the arrogant human need that the universe be created for them and that human consciousness is the basis for everything. That is religion, not science.
Or let me put this another way. Is consciousness an emergent property of the universe or is the universe an emergent property of consciousness?
i don’t like having to throw my hands up and say forget i asked, but the unsatisfactory state of affairs really does seem that unsatisfactory. like jean said, it’s preposterous on its face. my provisional acceptance is deference to experts, but if scientifically described reality is absurd enough, i’m bound to treat it the same as jesus showing up on my doorstep with a flaming sword. namely, shrug, close the doors, and go back upstairs. but i’ll read to the end anyways, since i did ask for it.
As I mentioned in my comment on the last page, there are possible ways to define an objective reality within quantum mechanics, but they tend to require so much carefully constructed cancelling of information to actually match with the equations and with observation that most physicists just apply Occam’s Razor and accept that there isn’t necessarily an underlying fixed reality as the simpler solution. Granted, ‘carefully constructed cancelling of information to actually match with observation’ is something that happens in many other places in quantum physics where we don’t have other options that we’ve found yet. See also ‘renormalization’.
Indeed, the idea that the quantum world is basically nothing but information, that any measurement ‘sets’ that information based on the type of measurement, and that there isn’t enough information in a particle to store more than the last measurement is an approach that can’t be disproven, even if it also doesn’t seem particularly helpful.
Part of String theory’s problem is that while at its core it is mathematically very nice, it also has its own internal fine-tuning problems to match with observations, and there are multiple incompatible ways to do that. This is part of the why people say it can’t be tested: almost any test that would disprove it could probably be worked around by just tweaking one or more of the internal free parameters. It’s not really a ‘theory’ so much as a landscape of theories.
@Jean:
While there are interpretations of quantum mechanics that actually do require conscious observers (check the ‘von Neumann chain’) most physicists really don’t like going there. And in the original Copenhagen interpretation ‘measurement’ was somewhat deliberately left vaguely defined. Instead, as I’ve noted in earlier comments, the interpretation that a lot of physicists seem to focusing on these days is ‘coherency’, where there is no single moment of measurement and instead the more any quantum state becomes entangled with other existing states the more it acts like part of a macroscopic system and settles on a particular value.
In this interpretation, think of reality as something like the surface of an ice cube right around the freezing point. Molecules of water on the surface can break off and move around as liquid, and there will be pretty much a constant layer of liquid. But any molecule that stays in contact with too many other stationary molecules that are part of the crystalline structure of the ice will be drawn in and fixed in place: that is the ‘measurement’. That same molecule can and will wander off later if the part of the crystal it was attached to shifts enough that there isn’t a firm grip on it anymore. So basically the ‘measurement’ is defined by the interaction of the particle and the environment that forces it into one of a small number of fixed configurations allowed by the environment: the constellation of allowed values is defined by the environment, but which one the particle fits into is based on the particle itself. And then, because the particle was changed by the environment, how it interacts with a different part of the environment later can be changed by its previous interactions.
Jean: There’s often been confusion about the word ‘observer’. Suppose you’re looking up at the sky. Photons are hitting your eye, and begin a process which ends up with signals being sent to your brain. But if you hadn’t been standing there, those same photons might have hit a plant and begun the process of photosynthesis. That is also an observation, with no people involved.
4 and 5 -- that’s better. and i think i’ve read these things before, but it’s been a while, and this stuff slips off my brain real easily.
Both 4 and 5 imply that you don’t have fungible particles because they retain information from (or are affected by) past events or are dependent from the environment in which the experiment happens. And that comes back to my previous point that the quantum model is incomplete. It’s not the observation that creates the measured characteristic but rather the initial conditions that are not known (and probably unknowable).
Jean @7: The Kochen-Specker theorem shows that you can’t have ‘initial conditions’ in the sense you mean. I’m sorry I don’t have a simple explanation of the proof of that theorem. I don’t think there is one. I can only say that if you specify such initial conditions, you end up with a contradiction.
@Jean:
The thing is, as far as we can tell, it’s not the quantum model that is incomplete: it’s the quanta themselves. A particle only has defined properties inasmuch as it has interacted with enough other things that those properties get locked down, and it only has such properties as what got locked down.
Let’s put it this way. You have a particle with a spin, and the axis can be pointing either up, down, left, or right. You can only measure vertically (up/down) or horizontally (left/right) at any given time. If you don’t know which way it’s pointing in a given measurement, the measurement will end up being a 50/50 coin flip as to which way you find it.
If you measure a particle vertically and get ‘up’, then as long as you keep measuring it vertically you will keep getting ‘up’ every time.
If you measure a particle vertically and get ‘up’, then measure it horizontally you’ll have a 50/50 chance as to whether you get ‘left’ or ‘right’. And if you measure it vertically after that you will have a 50/50 chance of getting ‘up’ or ‘down’. It’s like the particle can only have one bit of information saying which direction it’s pointing, and as long as you’re measuring it the same way you get the same result, but measure it in a different way and the particle gets randomized again.
And this is inherent; we have literally done tests of this where the decision on which way to measure the particle was made while the particle was halfway down the vacuum chamber and there was no way of knowing which measurement was going to be made until after it was made.
This is why we get the weird polarization filter effects I mentioned on the previous post, where if you have two polarized filters at right angles to each other, no light gets through, but if you add a third filter at a 45 degree angle to the first two and slide it between them, suddenly light will get through the three filters even when it wouldn’t go through the two.
As I said above, while it is possible to construct an interpretation of quantum mechanics where the particles actually have objective properties, the sheer number of weird things that would have to be going on to hide that from our best experiments makes that the more complicated explanation, even if it would make us feel more comfortable about reality in the process. Among other things, we would have to allow information to travel faster than light, but only as long as that information is absolutely useless in any macroscopic sense. (Basically the universe would have to be able to change a random coin toss to a different random coin toss, but since you didn’t know what the toss that never happened would have been, you can’t use any of the information.)
Consider the question of whether the universe is a simulation. It would appear that if our universe were discrete on all levels, that it would be possible for it to be simulated in any “higher” universe that has sufficient resources (including other-worldly “time”, allowing for sufficient o-w-time to perform any necessary calculations between each “tick” of discrete time in our universe). Then the consequences of any coherence could be calculated.
Is there any behaviour in our universe that could NOT be simulated? Alternatively, is there any reason to think that the universe might have a level (eg. time or spatial dimension) in which it is NOT discrete?
Given that it should be possible to simulate a (simpler) universe in our own, if the answer to those questions is negative, Occam’s Razor might lead us to believe that we are indeed in a simulation.