On the photon
I think this mysterious particle may hold secrets about the universe we have yet to discover. Moving at the speed of light, a photon moves from A to B yet experiences no time. It doesn't experience any distance either (in the direction it is travelling) thanks to length contraction.
So photons can reach anywhere in space in no time (from their perspective).
From our perspective as observers, if there were a “clock” on board a photon, it would appear to be entirely stopped to us. The Cosmic Microwave Background radiation was emitted 13 billion years ago for example so its ‘clock’ is still at that age.
Is it the case that wherever in spacetime the photon is travelling to must exist simultaneously (in some sense) with wherever it was travelling from in spacetime? IE there is no time or distance between the two from the photon’s perspective (between here and now and then and there). So does that mean that the past, present and future must all co-exist in some way? (Eternalism)
Clocks are roughly synchronised between the Andromeda galaxy and Earth (not much relative motion between the two) for this example:
A photon is emitted from the Andromeda galaxy 2 million light years away and arrives at earth. Does that mean that present day earth (in some sense) existed 2 million years ago when the photon was emitted?
So the photon is spotted in Andromeda 2 million years ago. The photon co-exists with Andromeda 2 million years ago. The same photon is spotted 2 million years later on Earth. So Earth ‘now’ co-exists with the photon co-exists with Andromeda 2 million years ago?
From the photon’s perspective, it is as if all time and space is compressed down to a single point - it can travel anywhere in space in no time. So does that mean everything in spacetime must co-exist in some sense?
When the photon sets off from Andromeda, Earth is at time 2 million years ago. When the photon arrives at Earth, what is the time from the photon’s perspective? IE 2 million years ago or now or both or neither? When the photon arrives at Earth, its ‘clock’ will still presumably read 2 million years ago? Is it that 2 million years ago and now co-exist in some way?
What is spacetime like from the photon’s perspective? Everywhere in spacetime it can reach travelling at the speed of light is effectively compressed down to the same point?
So photons can reach anywhere in space in no time (from their perspective).
From our perspective as observers, if there were a “clock” on board a photon, it would appear to be entirely stopped to us. The Cosmic Microwave Background radiation was emitted 13 billion years ago for example so its ‘clock’ is still at that age.
Is it the case that wherever in spacetime the photon is travelling to must exist simultaneously (in some sense) with wherever it was travelling from in spacetime? IE there is no time or distance between the two from the photon’s perspective (between here and now and then and there). So does that mean that the past, present and future must all co-exist in some way? (Eternalism)
Clocks are roughly synchronised between the Andromeda galaxy and Earth (not much relative motion between the two) for this example:
A photon is emitted from the Andromeda galaxy 2 million light years away and arrives at earth. Does that mean that present day earth (in some sense) existed 2 million years ago when the photon was emitted?
So the photon is spotted in Andromeda 2 million years ago. The photon co-exists with Andromeda 2 million years ago. The same photon is spotted 2 million years later on Earth. So Earth ‘now’ co-exists with the photon co-exists with Andromeda 2 million years ago?
From the photon’s perspective, it is as if all time and space is compressed down to a single point - it can travel anywhere in space in no time. So does that mean everything in spacetime must co-exist in some sense?
When the photon sets off from Andromeda, Earth is at time 2 million years ago. When the photon arrives at Earth, what is the time from the photon’s perspective? IE 2 million years ago or now or both or neither? When the photon arrives at Earth, its ‘clock’ will still presumably read 2 million years ago? Is it that 2 million years ago and now co-exist in some way?
What is spacetime like from the photon’s perspective? Everywhere in spacetime it can reach travelling at the speed of light is effectively compressed down to the same point?
Comments (37)
And then I wonder to what extent we really know that the Lorentz factor gives accurate answers for anything in the first place. But unfortunately I don't know enough about how we supposedly know this to critique the methodology. I'd have to research that.
To make a long story short, there is not really any solution to them, which is why the motto of modern physics is "shut up and calculate". However, at the same time, to excuse the pun, of course someone trained in these sciences does understand something of what these puzzles are and that there is no contradictions or paradoxes of the kind you describe.
It's not exactly true to say the photon does not experience "time" in the metaphysical sense. If time is change, the photon's "wave function" changes over "our time"; so this evolving wave function can be viewed as a metaphysical time. What the photon doesn't experience is classical time, or functional time which is the time that we live in. Likewise, it's a misleading shorthand to say fundamental particles "don't exist" between observations, but rather more accurate to say they don't exist in any classical sense.
We only observe classical time and classical particles, and nature has given us zero clue as to what things are really like behind our observations. For instance, we can easily assume from a metaphysical standpoint that there is some "substance" to a particle and some "mechanism" that causes it to appear on one part of the screen rather than another at each observation, but nature forces us to rule out any "substance" or "mechanism" that makes any sense to us.
To answer more directly your pondering, what "classical time" means is a series of regular events. Einsteins simple clock he used to build relativity and general relativity is two mirrors with light bouncing back and forth, let's say at 1 second per bounce. Let's now consider these mirrors at some speed away from us; now the light must bounce at an angle and travel more distance between each bounce to "keep pace" with the mirrors. Since light travels at the same speed to all observers (just take this as experimental fact for now), then from an observer travelling with the mirrors the light is simply going straight back and forth at 1 second per bounce; but from our perspective the light is going more distance at the same speed and so takes more than 1 second per bounce, therefore we see time for the fast mirrors pass more slowly than our own time (any repeating event, i.e. clock, we will see happening slower than the same setup up kept with us). Of course, an observer travelling with the mirrors can consider themselves at "true rest" and us travelling at a speed and comes to the same conclusion with the rolls reversed. In this setup since we are travelling away from each other, we never meet and who is "really at true rest" cannot be resolved. In order to meet, acceleration of at least one party is needed, which is like being in a gravitational field where clocks run more slowly for same reason that again light must travel a greater distance in a gravitational or experiencing acceleration, but this time the parties can meet and see that less time really did pass for the party that underwent more acceleration.
So the above is a "functional" view of time, based on light bouncing around and "ticking" regular events. So, let's now replace the mirrors with light and imagine that 2 light beams can bounce a third light beam between them. That light doesn't do this doesn't actually matter because all three beams must be going in parallel to "keep pace" with the clock, and so they never converge and never bounce, no ticks in this setup are ever recorded. From this, it is too far a jump to say the universe must therefore be a single point. First for a technical point that it's only 1 dimension that gets contracted, leaving 2 dimensions for all information to be represented in. Second, because our "classical time" is made up of events of fundamental particles. We cannot conclude that classical time is the "only time", and why would we? Fundamental particles must somehow go from one event to another between events, there's simply by definition no "classical time" available for this more fundamental time.
Light travels at the speed light obviously, but what's special about this speed is that it's the speed of causation, nothing happening at A can cause anything at B faster than this speed. What limits a particles speed is mass, and so any mass-less particle goes as fast as it can and delivers it's cause from A to B at the speed of causation. If the speed of causation was infinite, everything would happen simultaneously and classical time would not exist.
With this concept of speed of causation we can now more clearly see that anything going at this speed cannot experience any internal events, no clock can tick for it. But it's also true that our whole concept of experience relies on internal events, within a clock or our brain etc. and so there's no experience at all. A photon travelling between events does record any information and has no perspective as we understand it. So it's not accurate to say "it's clock is stuck at the time of the cosmic microwave background" but rather that the photon "has no clock at all", and so any questions about the photon's clock are simply functionally meaningless: there is no clock you can build that travels with the photon and no experiment you can perform that measures this unconstructed clock, so all questions about time for the photon are not well constructed questions.
We can accelerate things close the the speed of causation, but can never reach this speed and anything even ever so slightly slower can experience time and internal events and has a clock and there's no problem.
A photon is essentially an observation, and can only happen once. It is not possible to observe "the same photon"* twice, so it is not possible to observe whether any aspect of the photon "is changing". Hence the idea of a clock appearing to be stopped is invalid because, to appear stopped, at least two observations are needed.
*The scare quotes are there because even the expression 'the same photon' is of dubious validity. Ditto for "is changing".
As per my previous post, we cannot measure the 'length' of a photon, because that would require two or more measurements - one at each 'end'.
Note also that SR doesn't say an object moving fast relative to an observer 'has a shorter length'. It says the observer will measure the length as being short. Since length measurement is impossible for a photon, that concept does not apply.
To add to what Andrewk says about this, we can have a 2 dimensional space, it's no incoherent. Indeed, since 3 dimensional information can be recorded on a hologram, it's possible to consider physical systems existing on a "holographic" "true substance" and work out all the math and predictions we "think we experience" in 3 dimensions in 2 dimension. So (on top of being able to make coherent 2 dimensional spaces with working physics; such as a 2D computer game) we can even build a symmetric 2 dimensional universe that expresses a 3rd dimension implicitly. So contracting length to 0 does not create any fundamental problem.
The wave function could change but that is only our estimation of where the photon is; it is not the actual particle. Maybe the photon remains unchanged whilst its wave function evolves? That would fit in better with the photon experiencing no time?
Also it's clear that wave function changes in our time but does it in the photon's time?
Quoting boethius
So change is possible outside of "classical time"? The photon experiences no time yet goes from existent to non-existent in no time. Seems to indicate change.
This "more fundamental time"... would causation still apply to things in it?
Quoting boethius
So things travelling at the speed of light are beyond causation? This is what I'd expect for something that was beyond time.
Quoting boethius
We know that for something travelling at close to the speed of light, their clock runs slower and slower. It's not too much of a jump from that to fitting a clock to a photon for a thought experiment.
Dimension just mean how many coordinates are required to define a point in space; in our physics that really means an event in space as Andrewk points out. So you can simply define a physics system with 2 dimensions. A classical system is easy to visualize as it's like most 2D computer games: objects move around in 2 dimensions and interact based on rules.
Of course, we can't actually build a physical 2 dimensional system in our world (when described as 3 dimensions and not a hologram), as our world has 3 dimensions so there will always be interactions along the 3rd dimension even if we try to reduce those interactions by doing experiments on a surface. In certain particle physics contexts, due to the length contraction, certain problems can "drop" the 3rd dimension as it becomes negligible, but it is still there, so this isn't a good example.
That's my point, the particle does not exist in a classical sense between events; we are still free however to suppose there is some substance and some non-classical time to it's existence. The interpretation that the wave function is only probabilistic prediction of "where the particle actually is" does not stand up to scrutiny; all local variable theories have essentially been ruled out, so the "particle", insofar as we're still calling it a particle, does actually somehow exist in some sense everywhere it's possible to observe, we simply cannot make any description of it's "true substance" beyond this "existing in some sense at all the points it can be observe". If we interpret time as evolution of a system, what I called metaphysical time (as there's no experiment that is not functional "classical time" of clocks), this wave function experiences this sort of metaphysical time (doing these calculations to predict things has no physical interpretation; but we are free to suppose it might); the only reason to have such a definition of time is simply to remind ourselves that there could be a reality beyond our functional time experiments that we are unable to access (at least for now); for instance, there could be a mechanism that determines where events actually occur (selecting where in the probability space to actually show up); it's not metaphysically ruled out, but we have no way to ask this question in the sense of experiment (again, for now; that things could change with some revolution in physics, is the practical reason to remind ourselves of functional definitions of things may not be the true definition).
That you can define something in some way does not at all imply that the objective thing has those characteristics, does it?
Two dimensions isn't really possible. It's just an idea we have.
Hidden non-local variable theories are still in the running though?
It's entirely possible our world's true substance is a 2 dimensional hologram.
It's also entirely possible a 2D world really does exist somewhere out in the wider existence beyond what we can observe.
We couldn't build a true 2D physical system, nor can we build other universes of any dimension. But to say something doesn't make any sense, especially in a philosophy forum, is usually interpreted as some internal conflict in the idea itself, not that we simply can't build it. Also, it doesn't create a conflict to make a frame of reference arbitrarily close to the speed of light where the contraction is so great that it's dimension can be ignored, it doesn't approach non-sense to do so but is a physics trick called "boosting" that helps calculate certain problems.
Yes, this is what I mean when I say "some mechanism that determines where a particle actually appears", such a mechanism could be a hidden non-local variable theory or something totally different (maybe there is some deeper level that radically overturns our current quantum understanding, just as quantum radically overturned our classical understanding). A revolution in physics could lead to our understanding of functional "clock time" as emerging from some more fundamental time, that in turn could still be far from "true time". My use of the term "meta-physical" time basically refers to the fact we can always posit that something more is going on beyond whatever our current physical understanding of time is; i.e. today we are free to question whether there is a "time" beyond the closest clock ticks we can measure; and there are people working on theories where our functional time is an emergent property of something more fundamental; though it's very unclear if, even in principle, such theories could even have any physical meaning other than clever mathematics that happens to give right answer (predictions to experiments), just as building a mathematical framework based on holographic math doesn't imply the answers it gives is actually of a holographic system, it's just one mathematical path to the right answer (just as neither wave-mechanics nor matrix-mechanics has any preferred interpretive value beyond generating the right answers).
For instance, there is a position in the metaphysics of physics where the observation of particles is truly spontaneous, there is no mechanism of any kind but truly pure random occurrence manifesting with any particular observation; conforming to statistical rules but with absolutely "nothing happening in between" that determines if a particle is observed right or left, spin up or spin down. Although this seems difficult to accept, it seems equally difficult (to me at least) how to reject this view without a infinite regress of mechanism for the mechanism for the mechanism.
Oy vey. Say what? Why would you believe something like that?
It's possible because it can be mathematically consistent.
Why would you believe that things we can construct via mathematics might correspond to objective reality?
Constructing things with mathematics is simply playing a kind of game of sorts. You might as well think that the world might really be identical to Candyland.
You quote me saying 2 dimensional universe is possible, asking why I "would you believe something like that", I responded why I think it's possible. No where do I say I believe it is the case. I already qualified my use of possible as being internally consistent, not "buildable" and certainly I do not equate possibility with what is true. The context of my assertion is responding to the claim that removing length makes no sense; i.e. results in some internally contradictory scenario, to which I am pointing out that a 2D universe is not contradictory in itself.
Maybe the universe really is 2 dimensional, in the most naive form, but I have just been under the illusion it is 3 dimensional. I cannot dismiss the idea I live in a 2 dimensional world because it makes not sense, I must appeal to my experience and use induction to be highly confident the world of my everyday experience has 3 dimensions.
And once I am confident my everyday experience is 3 dimensional, there remains the possibility that reasoning and more subtle experiment convinces me the world really is 2 dimensional but stores 3 information that I experience as 3 dimension through something exactly like or similar to a hologram.
Whether the "true substance" of the universe is holographic is another question as different is the question whether it is a good pathway to make a better mathematical description of a theory uniting relativity and quantum mechanics (regardless of how we want to interpret what the math really represents, other than correct predictions).
The problems a holographic universe would solve, and why experts are working on the idea, is 2 essential ones.
The first problem is that the only arbitrarily precise measurements we can make are from an arbitrarily far distance, and in such a description we are completely free to then claim that the measurements at this arbitrary distance (what we actually observe) are what actually exists (strict functional approach to physics where we only view experimental results themselves as existing and any object we imagine to exist for ease of calculation is exactly that mathematical mirage you refer to, and there is strictly zero basic to assume that math represents anything beyond the correct answers it gives, which in this scenario measurements at an arbitrary distance); this arbitrary distance we can then view as "at the same distance" for all the measurements we make and this then forms a 2 dimensional surface upon which all our measurements exist (a particle accelerator detector is an example of trying to approach this method, and although the LHC detectors don't seem big compared to the size of the universe, they are immense compared to the size of quarks and other subatomic particles they study). Therefore, if our most accurate approach to modeling the physical universe actually takes place on a surface, then the 3rd dimension that we imagine constitutes the things "inside" our observation shell we can simply dismiss. So, from this perspective, the 3rd dimension of space is simply superfluous to the true (i.e. most accurate) description of nature we can make. Just as developing relativity required abandoning the assumption that time was universal (ticked at the same rate wherever you are) and our quantum theory required abandoning the assumption particles have a precise position and momentum -- in other words just as relativity and quantum required abandoning our expectations of how the universe works based on ever day experience, where time does really does seem universal and constant for everyone and everything we can hold and toss in our hand really does seem to be really there at a well defined position and momentum -- maybe the next revolution in physics requires us to abandon the idea the universe has 3 spatial dimensions even if our everyday experience really strongly suggests space has 3 dimensions (of course, such a theory would still explain why we experience 3 dimensions, just as relativity explains why time seems pretty constant and quantum explains why big objects seem pretty discrete and determined in position and momentum).
The other reason, which is beyond simply a minimalist strict experimental functional approach which has helped us in the past, is that quantum systems seem to have a "non-local" communication within them (which just means things happening faster than the causal speed limit I've already referred to). Though we can't exploit non-local communication within quantum systems to actually pass information around at faster than light-speed, it's difficult (and most experts agree is impossible now) to explain the result of certain quantum experiments that have things happening at a distance (and then those results brought together at equal or slower than the causal speed limit to analyse them) without non-local information transfer within the quantum system. One property real physical holograms have (not 3d illusions based on parallax but real holograms), is that information is stored on them non-locally. If you cut a hologram in half, unlike a normal photograph, you get two smaller copies of the whole hologram each with less resolution. So, if the "true substance" within which quantum phenomena is really happening is holographic, then the information of the universe is stored non-locally and there's no puzzle about quantum systems seeming to communicate non-locally; this non-local information holding "holographic substance" has rules that give rise to our rules of accessible information never travelling faster than our observable causation limit, but quantum systems use the non-local aspect to resolve the results of experiments.
Of course, even if the holographic principle does play a central roll in our next physical theories, that doesn't imply it wins the "true substance" argument or even that such an argument can ever be won. Maybe out next, next physical theory will describe a 2 dimensional holographic surface within a 3 dimensional space and that parts of the the surface can interact with other parts through the 3rd dimension of this space, which appears to us like energy disappearing and reemerging through a 4th spacial dimension in our experiments (in more naive, less accurate description that don't take into account things are really a holographic spherical surface within a larger higher dimensional spherical space).
I was saying it makes no sense as something that could actually exist, not as an abstract construction.
Hi Devans,
I had this same thought regarding the timelessness of photons a few days ago.
Imagine a pair of entangled photons/ particles emitted in the early universe. One photon makes its way over billions of years through the entire universe to land at a detector at present day Earth. Its spin is then measured and so the spin of the entangled particle is then known.
However the entangled photon could have interacted with a particle billions of years in our past, or even billions of years (or more) into our future. Yet these two events happened simultaneously as viewed from the photons' entangled states.
A conclusion I could infer is that the whole universe is predetermined, macrospic time is therefore merely an illusion. It might be true to say that the whole universe lived out its entire existence instaneously through quantum intereractions. We are now merely witnessing the realtime effects of all these interactions play out...
I've already presented several arguments that a 2D universe could actually exit.
First, there could be another universe that actually exists detached from our own.
Second, our universe could be actually a 2D hologram.
Third, we could actually be in a 2D universe in the straight-forward sense, but have both mistakenly interpreted our experience as 3 dimensional. I.e. we must verify with our experience the dimensions of the universe, we cannot reason that it's impossible there's a 2D universe out there and rule that out a priori.
Do you see faults with the above arguments?
If you're using the term "non-sense" to mean "not a sensible interpretation of our experience in our own particular universe", then yes, I'd agree that 3 dimensions is a good conclusion to draw from our experience. But there's a difference between "not sensible in itself" and "not a sensible conclusion from our day-to-day experience".
Your original argument was that length contraction to zero at the speed of light made a non-sensible interpretation of the world and therefore there's some sort of problem. My points above are that the conclusion does not follow, nonsense is not the result of length contraction to a 2D description of reality (it's completely acceptable in our theories and is sometimes done on purpose to simplify certain calculations).
299792458 metres per second is the speed of light. If you had a distance of 2 light years (thats a distance not a time period) it would take 2 years for a photon to travel that. What you are touching on is special relativity and some other things. Yes a clock that approaches the speed C will tell time much slower than a clock moving on the earth (the earth is moving). This has been proven on airplanes that move faster than clocks on earth (in proportion of course). A photon does not move instantaneously but just fairly fast as far as i can tell. Ofcourse i'm sure you've heard that nothing can travel faster than C but i guess some scientists say that isn't true.
i see what your saying. When matter and energy comes to a standstill who knows what that is like. i used to be a bad wrestler in high school and when you are on your back and there are 20 seconds left on the clock those 20 seconds feel like 10 minutes.
There is no functional definition of time from the photon's entangled state. No clock can be built to tell us this event happened simultaneously; we can only make a clock that records the time of experiments; so in this case when the two particles were observed (which due to relativity has no absolute definition of simultaneous already), and from there we can note a correlation between the results of experiments of the entangled particles. However, it's not meaningful to say that the photon's experienced the observation of the entangled variable at the same time; photon's do not experience anything at all and have no perspective and no functional time (no clocks) ever tick for any photon.
Your argument could be reformulated without functional time, with a context of some form of meta-physical time. I'm not sure how that would be done, but it's important to have clearly in mind what observable time is in these sorts of arguments.
Quoting Jonmel
It's not clear to me how your inference works. Entangled observations still happen at moments in time (in whatever frame of reference you want to choose), and what makes entangled observations strange (in most interpretations of what is going on) is precisely that they are not determined, an observation does not reveal a correlation that was already present (hidden local variable) but brings into existence the observation and correlation (a non-local link between the observations). However, there is nothing instantaneous between the event that created the entangled pair and the time one or both are observed. Likewise, the speed of causality is not violated as we cannot use what appears to us as instant communication between the entangled particles to communicate any information at faster than light speed, we can only bring results of experiments together at sub-light speeds and note interesting correlations between the results.
Quantum phenomena remain bound by the speed of causation, so it's not clear how an inference would be made that all events happened instantly.
Time does not pass in the frame of reference of a photon, but what is really going on is that the speed of light is not an admissible frame of reference. The speed of light remains the speed of light in all reference frames, and a light beam world line (in a sub-light speed reference frame) cannot be transformed to be at rest. What "from the perspective of" means, in a physical sense, is that the thing in question is considered at rest and everything moving relative to it. This transformation of the coordinates everything is following can be done for all sub-light-speed particles and observers, and the paths of everything else relative to the thing we're now considering at rest worked out. However, no matter how much we try to transform the path of a light-beam to be at rest it can never be done, light just stays at light-speed. So, there's simply no sensible formulation of the "frame of reference" of a light speed observer: it's impossible to have such a frame of reference in our physics. The point is, arguments are not sensible from a non-sensible frame of reference (i.e. "what light experiences" or "from the perspective of a photon" etc.).
Of course, there's plenty of theories, both predating and postdating quantum mechanics, that the universe is pre-determined and both the past, present and future already exist and experience is an illusion.
Hi Boethius,
Thanks for this, maybe we need to define (or take as assumption) that the functional definition of time for an entangled state, or indeed that of a waveform, is zero or instantaneous. This could offer insight into quantum phenomena such as observed in the Delayed Choice Quantum Eraser experiment - https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser - where the choice to measure the interference of an entangled photon is made after its pair has already hit a detector.
Conventionally time is measured as progressing steadily forwards in a local frame, relativity then accurately describes different references frames. However, as you note, it is not possible to define two events as occurring simultaneously under this framework - an observer will perceive the timing of events dependent on his location.
An old analogy is for an observer moving away from a clock tower at the speed of light. He will always 'see' the same time, hence for a photon time is not progressing in the conventional sense. If an entangled pair of photons exist in a state of zero time then they would indeed be able to exhibit interference, or have opposite spin, when detected at any locations across the universe. These detections can then be assumed to be simultaneous under relativity so that the frame of reference for the entangled state would be precisely midway between the two observations. Could this explain quantum paradox?
Yes, I alluded to in an above comment that functional time does not exclude metaphysical definitions of time. For instance, the time between clock ticks (i.e. the shortest and most accurate clock ticks we can make) has no functional definition, but we are free to presume that there is a non-functional time that does pass between clock ticks. Likewise, the "time" used to progress quantum states between observations is not functional (by definition we are not making any observations, about anything including clocks) and again we are free to employ and use a non-functional definition of time to try to understand better what is going on.
You may have noticed that I, and others with training in the math of relativity and quantum, have a strong tendency to avoid any interpretation at all. And, many professionals would hear "metaphysical time" and react immediately that the conversation is meaningless.
However, by trying to understand "what's going on" from different metaphysical points of view (that, should be noted, cannot be eliminated altogether: functional time depends on meta-physical definition and intuition of time to be formulated), in my view is productive way to clarify ideas as well as generate new ideas.
So these conversations I fully endorse, whether between professionals or amateurs.
However, once one understands the math ... it's very hard to actually come up with interpretations or any candidate for "true time" other than "that time in which clocks tick". Quantum and relativity have a way of making any real change to these theories essentially unthinkable, and the theories themselves have a way of making any access to the underlying reality (the "true substance") completely opaque. For instance, questions like "is 4D space-time a single 'material'?" and "what 'decides' any particular quantum observation?" have no sensible answers. Relatively presents space-time as a 4D "object" that is static (yet we experience time) and quantum theory rules out any "hidden local variables" that determine the results of any given experiment in a "sensible way", and yet any particular experiment has a result (we really do experience only one of the probabilities, and yet quantum theory essentially rules out even the possibility in principle of getting any insight ever into what makes a particular experiment spin up or down, the detector activate here or there).
What's even crazier than perfectly sensible questions being eliminated in principle from our theories (unlike in Newtonian physics where universal time goes forward moment by moment and any process will be wholly determined by probing smaller processes that make it up), is that our two theories are not mathematically compatible.
As for the issue at hand, how "entanglement works" again has no sensible approach to answering in quantum theory as it exists today. It simply is what happens, there's no way to explain how it happens. But it is not actually much more bizarre than other quantum things, it's just we've gotten used to each individual experiment being "purely spontaneous" and the uncertainty principle between momentum and position. What's different with entanglement is only that it took more time to rule out completely every local variable possibility.
However, there remains the possibility of a complete revolution in physics as profound a change as classical to quantum. But within the context of the theories as they are today, everything does make a lot of sense. There's not some trivial or obvious nonsense happening with modern physics theories; this is the basic point I'm trying to make in this thread.
Going beyond our current understand is a profoundly difficult and subtle undertaking. A lot of really smart people created our theories, made them work and many of these same people also tried every way they could think of to make it "sensible". Nevertheless, it is a journey I wholeheartedly encourage anyone to join.
But it can't, because the actual world in no way hinges on stuff we just make up in what's essentially a fantastical manner.
Hi Boethius,
You make some interesting points. I suppose the whole point of philosophising is that one seeks to understand the underlying reality, gain insight or interpretation which could lead to leaps of judgement so that the maths can be developed or experiments can be devised which would prove/ disprove new theories about reality. I feel we're only just beginning to scratch the surface of what science can reveal about this universe. From general and special relativity through to QED, these theories are incredibly accurate and powerful and I'm sure they will be built on in the future. Maybe the whole point is we will never fully understand concepts such as consciousness but I'm certain we will continue to unravel the mysteries about the nature of reality.
Take inertial mass and gravitational mass. Experimentally these have found to be identical although there is nothing to indicate mathematically that they need to be. However it seems intuitive to me that they should be the same. An object accelerating through space is equivalent to a large body deforming spacetime. Does this mean that acceleration also causes spacetime to deform?
Liwewise quantum behaviour seems somehow intuitive - we now have a limit to how small particles/ energy can become. Things seem to jump about and exhibit non-local behavior because they are discrete, quantum properties can only be ascertained by disturbing/ interacting with a particle, time as we know it fizzles out into a blur of nothingness.
Mathematically we can make predictions about experiments and know that this form of logic works 'in the real world'. However I believe further that mathematics, logic, and consciousness forms part of the real world, they are intimately connected - mind/ reality are one much like energy/ matter are one. There is no reason to believe that the universe should be understandable, or describable, or even coherent - but mathematics has proven that we can gain insight into the universe we are a part of.
Quoting boethius
There is a duality between Relativity and QED where it seems there is an impasse. However we know they are both solid theories, maybe it is impossible to reconcile these two perspectives and progress is to encompass both. Quantum experiments show that two realities exist in confluence - timebound, discrete particles and timeless, non-local wavefunctions.
I agree with your definition of the difference between classical and quantum time (what you seem to call metaphysical time). But if we deem a series of events to be random - like radioactive decay - we should specify by what time line they are random. They are only random according to the classical time line but does that mean they are 'truly' random when measured by quantum time? It may be that in quantum reality radioactive decay may be perfectly regular and predictable (maybe all such events are even simultaneous.) In mathematics it is easy to create a function with a regular input but a seemingly random output.
I am not equating classical and metaphysical time. One could do so (that there is a newtonian-like world beneath our ability to observe), but by metaphysical time I mean to refer to any and all definitions that are not observing clock ticks.
Quoting EnPassant
The randomness issue is not directly related to time definitions, but to whether there are hidden features that we can't observe.
The position that there is not any randomness in a Newtonian sense, is called "hidden variables theories", but you can imagine that there's just small "springs and gear mechanisms" everywhere (that we can't observe) that fully determining how every event turns out; the internal states of these tiny mechanisms are the hidden variables. Actually building such theories is usually highly abstract and don't generally involve tiny springs and gears but deterministic fields or just deterministic abstract variables added to our existing theories: variables we cannot, and can never, observe; they just remain an unknown and the probabilities are built-up out of our lack of knowledge; just like if I shuffle a card deck I can predict a 1 in 52 chance of flipping over any card due to losing track of the variables, but the event is not spontaneous since if we do keep track with a high-speed camera we can work it out, unlike radioactive decay -- current quantum theories, as they are used, simply give us directly the probability curve of radioactive decay or any other event; it is pure spontaneity.
Physicists generally take this pure spontaneity view because there it makes not difference to add variables that have no consequence on the results; so there's no practical reason to think in terms other than pure spontaneity. Of course, not everyone, those working on hidden variable theories have a different view, and I'm sure there's some physicists that don't view hidden variable theories as fruitful to work on, and would bet against them coming up with any new prediction, but do not believe in pure spontaneity from a metaphysical point of view.
And, according to quantum physics things will stay with the pure spontaneity in terms of how predictions are made, but we can't exclude a revolution in physics next year or a thousand years from now that changes this perspective.
The definition of space and time would likely be a central part in any revolution in physics, but not necessarily relating to the spontaneity issue. Quantum gravity would be a revolution in physics, and the main approach for a while was to simply try to fit gravity into our Quantum theory and behave like the other forces (reduce everything to the quantum paradigm and call it a day); it's only the failure to have done so that has led physicists to more radical frameworks, that redefine time and space differently.
I'm not sure what you mean by everything happening simultaneous. If such were the case there would be no cause and effect?
Quoting EnPassant
Yes, hidden variables theories are when things are determined by features we can't observe, represented by variables that we don't know anything about and functions that transform those inputs into outputs; but since we don't know the inputs we can only evaluate the probability space of the outputs -- which happen to be worked out to exactly the same predictions as quantum physics currently provides without the hidden variables.
Well, that was a throwaway comment. What I mean is anything could be the case for all we know.
Here is where my thoughts have led.
Space is two things. It is an ontological reality and a geometric reality. Ontologically space is there. It is not nothingness, it is a substance. But space as geometry seems to be more accessible to science.
Can it be that ontological space can simultaneously manifest more than one geometry or spacetime? It seems to me that quantum spacetime and classical spacetime (ie the macroscopic 4D world) exist simultaneously in the same ontological space. The spacetime that particles live in seems to be some kind of exotic N-dimensional geometry that is not classical.
I think it was Bohr that said it is meaningless to talk about where a particles is, outside measurement by a device in classical spacetime. In this respect 'where' means a position is classical spacetime. Apparently it is nowhere in classical spacetime at all, it is in quantum spacetime (geometrically speaking).
We don't see particles, we only see trace effects. A spot on a photographic plate is a trace effect, not a particle! What is important here is to see the both the detection apparatus and the trace effect are macroscopic, classical objects; they both exist in classical spacetime. This means that the trace effect is necessarily a classical object, obviously located in classical spacetime. But where is the particle before/after detection? Nowhere. Nowhere in classical spacetime that is. This is why Bohr says it is meaningless to say where it is. It is 'elsewhere'.
If there is a light source at A and a photographic plate at B and a photon is detected it is natural to assume that the photon travelled in a straight line from A to B. But, strictly speaking, all we can say is that the photon left a trace effect at A and a trace effect at B.
But these trace effects are classical objects and a straight line joining them is also a line drawn in classical spacetime.
If the photon is not really travelling in a straight line (because it is not even in classical spacetime) the straight line must be seen as an artefact of the experimental apparatus itself. This is because the whole experiment is taking place on 'this side' of the interface between these two spacetimes. Consequently any relationship between trace effects must be in terms of a classical 4-D geometry. That is, the positions of particles (in reality trace effects) is imposed on the situation because the experimental apparatus, being a classical object in classical spacetime, can do nothing else but force things into a classical geometry.
Yes, I agree, Kant's noumena, the thing in itself, could be anything.
When I mention we may have a revolution in physics that may change completely our concepts of time and objects ... likely we will still be wondering about the noumena.
Quoting EnPassant
Yes, one way to put this distinction into relief, is that we could conceptualize living in a world that has no regular clocks or rulers. We could perceive and do things but could not make any geometry, as we currently understand it.
Quoting EnPassant
I am also partial to reducing to Borhs view, in terms of what we are really justified (at the moment) of taking.
It's not a popular view in "physics discussions", but that's because it doesn't give many ideas; visualizing different interpretations is generally more fruitful, but when physicists ask after a bunch of talk of "what are the observables and what are the operators" I generally take this to imply at the end of the day we need to get back to Borh's view to see what's, if anything, has been accomplished.
However, there is an alternative view, I believe most associated with Dirac, which is the goal is to build a physics theory that describes the quantum realm, describes our apparatus that probes the quantum realm and describes ourselves and to fully get rid of the "classical apparatus of the eye, computer screens and detectors". From what I can tell, this view is gaining a lot of popularity. As far as I know there's no epistemological basis to reject this view, just that it hasn't succeeded yet. Though my feeling is that someone with enough skill and knowledge could still make a very robust defense of Bohrism.
Quoting EnPassant
The core of quantum theory is that we cannot "see particles" like we can see large objects; all the math just transforms initial conditions to observables that experiments can probe. Particles are also not really assumed in quantum physics, they are just an analogy for quantized field vibrations, and quantized fields are basically just an analogy for abstract mathematics (abstract spaces that contain all the variables and operators that convert the variables a probabilistic prediction of what a given probe of the system will find) that tie the initial conditions to observables.
Because this is the view and we never actually see what's "happening in the middle", we only ever observe on the sides of quantum phenomena, things have been recently reduced even further to the surface area around our system, such as a particle accelerator (where the detectors are essentially infinity away compared to the size of a quark which is being probed), black wholes (where information must be somehow "on" the event horizon), as well as the entire universe, where in each case we observables are tied together and we can forget about there even being a middle, what is referred to as "the bulk" -- we live in and perceive the bulk, but it seems we don't need it to do physics ... maybe.
For, another theory being worked on today reduces things even further to just "events" that are all discrete and individual are not in a "space" but have a network of relations between them which gives rise to the illusion of space, time, particles, fields etc.
Quoting EnPassant
Our apparatus is definitely classical, but it's a fairly radical direction to claim our apparatus imposes anything on the quantum realm ... as this seems to imply the apparatus exists first. To understand the limitations of what we're able to observe doesn't require giving up the assumption that we're made up of smaller things and that smaller things are causing things to happen in our apparatus. So to say our apparatus force things into classical space-time, is extremely ambitious. It's not required to go that far, though I wouldn't say on a philosophy that you can't go that far. The less extreme view is that we just so happen to live on a scale where thermodynamics affects us, we have definite observations, and how this arises from our various many parts is somewhat of a mystery: that entropy was low in the past and that quantum probabilities do resolve into something definite at some point between us and our parts / experiments; are both unresolved mysteries, as far as I know, that give rise, in addition to general relativity and the standard model, to our classical perceptions.
What physicists generally view as "what's really real" are symmetries and symmetry breaking.
If there was no symmetry then nothing would stay the same from time to time or place to place, and there would be no time or space to begin with, and so nothing could have any identity (which we seem to have, so we don't live in a universe with no symmetry) and if symmetry was never broken then everything would be exactly the same everywhere and again there would be no identity apart from the whole (and we seem to be a separate part from everything surrounded by other similar separate parts, and so again we don't live in a fully symmetric universe).
So, although we can't really visualize the "true substance" and there can always be smaller features we can't see at the moment - and may never be able to see - we do know that whatever the true substance is that we live in, it has real properties of symmetry as well breaking of that symmetry; and when we think about what it is to "know a substance" it is to know properties of it, so in this sense we do know something fundamental of the noumena that is beyond simply our observations. What we don't know, for now, is exactly how all the symmetries and symmetry breaking fit completely together (but we do know a surprising amounts).
What I'm saying is that the geometry is imposed on the trace effects that register on photographic plates etc. It is not the particle that is being observed but the trace effect (eg a spot on a photographic plate). The point is that these trace effects are necessarily classical objects and any geometry that relates them is going to be a classical geometry.
Suppose you have a light source at A and a photographic plate at B with a spot made by a photon. Here are two trace effects with a straight line joining them. It is natural to assume the photon travelled in a straight line between A and B. But since photons exists in some exotic quantum geometry we cannot really say it travelled in a straight line, not least because it does not even live in our classical world.
Where then does the straight line come from? It is an artefact of the experiment itself. The experimental apparatus is a classical object in classical spacetime and likewise with the trace effects that are collected. Given this, the only geometry these trace effects can have is a classical geometry. But this tells us nothing about how the photon travelles from A to B since it is travelling in its own spacetime.
The crux of my idea is that there are two distinct spacetimes (quantum and classical) made manifest by ontological space. These spacetimes exist 'here' in our ontological space but because they are different geometries they are, from a geometric perspective, two different spacetimes.
The trace effects exist at the 'edge' between these two spacetimes, but on the classical side of it. The photon exists on the other side of it. So how can we measure quantum spacetime with classical rulers?
This idea of interactions between two spacetimes/ dimensions (classical and quantum) must carry some weight. It is the interaction between the continuous classical world and the timeless quantum world that holds reality together, without one or the other substance would dissolve into nothingness.
On the macroscopic scale, what we see and interact with is only a tiny fraction of what lies behind. If you look at a tree, you only see a few of the photons which have recently interacted with the tree. The vast majority of stuff which makes up the tree exists in a seperate quantum dimension which we can only probe into. Yet it is these interactions which holds the substance of the tree together. With small electromagnetic force interactions constantly tugging and pulling through all the branches, the quantum fuzz of the tree is brought into the classical world.
I am not educated in QM or Relativity beyond a smattering of readings of science popularizers, so my question might well be naive. If there were "hidden variables" that determine quantum events, would those hidden variables be self-determined or determined by "something else"? It seems to me that nothing is solved in either alternative, it just pushes the explanation back one step further. And with the alternative that the hidden variables are determined by "something else" an infinite regress seems to threaten.