a gravitation wave is what?
15 Jan 2015 16:17:47 UTC
Topic 197930
(moderation:
Is a wave as in gravitation wave or electromagnetic wave considered as a disturbance in spacetime?
If GW don't exist, then disturbances at a distance are possible without waves. But hasn't particle physics already shown this to be the case in some instances?
merle
What is freedom of expression? Without the freedom to offend, it ceases to exist.
— Salman Rushdie
a gravitation wave is what?
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Well as Isaac and Albert used to say......
RE: Is a wave as in
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Gravity is, electromagnetism isn't. For electromagnetism the wave is a variation in the value of a field which exists at every point in space, but we leave the space and time co-ordinates alone. In General ( & Special ) Relativity we muck about with the meaning of the co-ordinates in and of themselves.
Merle you have indeed poked at the key thing. The very thing indeed. I'm not going to really answer the question because it is the exact moot point that remains elusive ! :-) :-)
So I'll defer to presenting a precis of my personal take on this. A sort of reasoning as to why there is a gap in the reasoning. Prepare yourself for a weird discussion. To prevent insanity I tend to take the approach of :
'What mental models do we have that accurately describe what we experience ?'
This slides around all manner of unproductive existentialist type rhubarb, fascinating though that may be. It keeps one closer to the action. This means that to answer what yourself - and many others - have queried requires a definition of 'particle' and 'wave'. At a minimum. Now when I say 'mental' model then ( in the area of study called physics ) I imply also an enclosed mathematical apparatus that makes such modelling precise enough to take into experimental scenarios. The precision that numbers yield means that predictions from competing models may be disambiguated upon by sufficiently precise measurement ie. can the 'distance' b/w two models that claim to explain some real world experience be distinguished when we look ?
Pretty much by definition, in everyday traditional language at least, wave and particle labels have opposite or complementary flavours. In the sense of dividing the universe into things that are either in the set of waves OR in the set of particles, with nothing whatosever in the set intersection. So that 'OR' is meant as exclusive ie. never both ( the intersection of the wave set with the particle set is the null or empty set ). Particles are localised, waves are extended. Waves vary smoothly, particles are lumpy/chunky. Waves have phase that may interfere separate sources, particles ignore each other. To add to the confusion, at different times in history separate actual attributes are applied to these notions. So a classical theorist circa 1850 has an idea behind the word particle that doesn't equate ( but may perhaps resemble ) what a quantum theorist is thinking of in 1950.
Now you could say : 'stuff the words, what does the real world do?' ie. go out and look around and deal with the labeling later. In effect this has been done and what is found is wave or particle behaviour depending upon how you went about it. Many find this quite infuriating and I agree, this being at the precipice of insanity, as it were, alluded to above.
I won't retrace the excruciating historical detail but use a more-or-less everyday example to illustrate. In the olden days before CCD camera back planes one had film to make a visual record. Snap a photo by exposing the film to light suitably focused. To view that image, after film processing to firm up the state of the substrate, one shines light through the film onto some screen. Thus you get, at least vaguely, a representation of some light patterns on the day of the exposure but replayed.
The wave explanation of this optical exercise is that of diffraction. Both for the original image recording on the day and subsequent rendering on some screen later on. You can consider the processed film as a type of interference device sending incoming waves from the film projector's lamp through a sort of maze with various time/phase delays per path.
The particle explanation is probabilistic detours of large numbers of photons traversing the exposed film, with not alot happening b/w light bulb to film, and from film to screen. Almost all the quantum action is inside the film. If you try to detect/measure the 'actual' path taken by any given photon then you destroy the coherence of the image. In fact with all gadgets thus far attempted that try to define 'which-way ?' you wind up materially changing the experiment.
So there are really two experiments. One is the experiment that you did without which-way detectors, the other is the experiment that you did with which-way detectors. Crucially : there is no observable result obtained from either one that enables you to explain the other. If you try you will get contradictions very promptly. A short dead-end street indeed. You see, one expectation of localised particles is that they don't take two routes at once. So I go to work each day via one of two intermediate towns, never splitting either myself or the car.
Currently we are left with a pretty knife edge situation. A very special type of thinking and procedure must be followed to usefully use quantum mechanics. I would describe it as a willful disobedience of common sense. Localised detection of phenomena gives you particles eg. a photodetector giving one click per photon arrival. All or none, and no fractions. If you broaden your measurement in space ( a bigger light bucket ) or in time ( wait for longer ) then you'll see waves as a herd characteristic.
The classic two-slit Young's interference experiment has been performed with a very low rate of energy transfer from source to screen. The guy went sailing for a number of months and then came back to develop the film. Provided the total energy transfer was the same, the pattern was no different than if he'd done the exposure in five minutes. That is : the energy density of the radiation in the apparatus at any given moment was both irrelevant to the measured outcome and did not serve to distinguish models. Go figure !
Hopefully the long way around is the short way home here ! Back to the question :
Correct, for a given definition of 'wave'. :-) :-)
Correct, for a given definition of 'particle'. :-) :-)
And yes, this is very bloody annoying !!
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
RE: RE: Is a wave as in
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Thanks very much Mike,
Your answers help me to validate(or not) what I think and then it gives me a more refined way of looking at the problem even though I'm sure I don't completely comprehend all of what you said. It seems then that when you get to the sub-atomic world the best thing is to just throw out the old ideas of particles and waves and start with a whole new way of describing "reality" at a level more basic than particles or waves. There MUST be words to describe these goings on without just referring to equations.
Just dream up a totally new vocabulary and do not use those words at all.
Easy said, I'm sure. And perhaps naïve.
merle
What is freedom of expression? Without the freedom to offend, it ceases to exist.
— Salman Rushdie
So too, I would say that
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So too, I would say that really at a fundamental level neither particles nor waves exist. That has already been proven by the fact that they contradict one another. They are simply a somewhat convenient way of describing certain limited segments of reality.
Yes or No?
merle
What is freedom of expression? Without the freedom to offend, it ceases to exist.
— Salman Rushdie
RE: Thanks very much
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Ah welcome ! You are now officially a member of the quantum club. I am sure I don't completely comprehend all of what I said. Take a seat and settle in with me and some other really great company much more famous than either of us ! They are way smarter than us, their ignorance margin is narrower than ours, but they also are sure that they don't completely comprehend all of what they say !?!?. ;-0
That's pretty much my take on it. I force myself to think of these really small things as 'entities' : that is the actual word I use myself in my mind. That way I don't prejudge the reality, so to speak. That leaves the 'truer' definition to be dealt with at the level of the detail of the modeling. There is a really old Zen (?) saying "don't confuse the Moon with the finger that points at it", meaning a thing has it's own reality quite separate from how it is indicated or identified. For me a thing is better characterised and intellectually handled by it's behaviour rather than any label that might be assigned to it.
[ I recall Richard Feynman discussing how we sort the chemical elements in order into the periodic table. Someone interjected claiming a 'circularity' in the definitions ie. Boron has five protons but something with five protons is arbitrarily called Boron. He replied with something along the lines of : 'as a language exercise that is true, but there still remains the fact that these things independently exist and we desire to explicate them'. Top answer ... ]
Yup. Strictly speaking it's an inappropriate application of human scale ideas - words too - into another realm. A poor extrapolation.
I can point out for you quite exactly where within the mathematics/modeling of quantum mechanics is the intersection/abutment of wave and particle aspects. But first go and pour yourself a cup of some favorite beverage and why not load up a plate with tasty snacks ...
The existence and time evolution of some system of interest is represented by a state function, a mathematically smooth thing of 'wave' quality, undergoing transformation to another state function later on. There is a process represented by the Schrodinger equation that let's you morph the original function into the newer one. But this processing does not involve any disturbance from without. Hence while we use this method we have not mentioned any experiment ie. a measurement or what it may yield. Our gadgets don't measure state functions. They give some reading of some real quantity. The wave function is NOT representing a physical quantity with any units, AND it is NOT directly representing probability either. It is however deemed to be a full representation of some system at some time, and by various mathematical procedures one can derive a number(s) from it to take to the lab and check the correspondence b/w theoretical prediction and what the something-or-other-meter is reading. Got that ?
It is in the getting of the number(s) out of the state function to take to the real world where the intellectually squirelly stuff is. Imagine a square piece of wood about the size & shape of a chessboard. Paint it some color like pure white for instance. Do this really well, so that when you look up close at the board's top surface you can't tell by any features ( because there aren't any ) where you are on the board. No matter how closely you look. If I took a really fine-tipped pen/marker I could then place a dot on the surface wherever I wanted. The dot clearly indicates where I did that. That region of the board is now distinguishable from other parts. Let's for discussion call that the Smooth Marking Case (SMC), this being an analogy of pretty much how classical physics goes about it's measurements. For any quantity of interest the variation of it's possible measurable values is smooth without gaps or disallowed values. So if I have a classical voltmeter, say, that measures b/w 1 to 5 volts then I can get absolutely any value in between, essentially only limited by my patience and how steady I hold the marker pen, so to speak.
Now get out the black paint out, carefully rule up the typical chessboard grid and get painting to yield an actual serviceable chessboard. The black/white pattern now gives the surface some features like : 'this is a black square', 'this is a white square', 'this is the boundary b/w a black and a white square', 'this is the junction of two such boundary lines' and even 'this is a square on the edge of the board' or 'this is a square at the corner of the board'. And so on to perhaps even higher derivative statements that tiptoe into the rules of chess like 'this white square is not the right color for the black queen to start a game on'. Call this the Discrete Marking Case (DMC), because now when your marking pen is hovering over the board the rule is that you cannot be arbitrary with your choice of position. There will be some scheme that says you can only mark white squares, or only black squares, or only at color boundaries etc. So my quantum voltmeter while having the same range limits as the classical one - from 1 to 5 volts - has disallowed values within the range. Maybe only 1.0, 1.1, 1.2, 1.3 ..... 4.7, 4.8, 4.9, 5.0 are achievable perhaps.
Hopefully by now you have sensed the gag. The state function has smooth variation like a blandly colored board. If you want a measurable quantity you have to lay a grid onto that, and you can only get values that agree to the 'rules of the grid' - whatever they may be. The marking pen is now constrained, and what is even worse is that one can no longer guarantee that any particular mark will be made on any specific occasion. Just prior to measurement, with the pen hovering as it were, you now have a set of potential outcomes ( called the 'measurement spectrum' ) each of which is assigned a probability that it will be the chosen one when the measurement does occur. Quantum mechanics makes NO statement whatsoever as to why a particular dot on the board is chosen. Mathematically the derivation of the probabilities from the state function is performed by mathematical beasties called 'operators', these 'operate' upon our smooth state functions to give those odds. Different smooth wave/state functions contain encoded within them the especial probability values for each and every possible measurement outcome. The operators divulge the 'preferences' a state function has for the measurement outcomes. The mathematical evolution of functions is enacted via the Schrodinger equation, which correctly transitions the functions to reflect the proper evolution of the system in time according to more general & already well known principles like the various conservation laws. When the pen tip contacts the board, the measurement is realised from a set of potential hopefuls, the whatever-o-meter goes click, the particle has arrived etc.
The full horror is that the measurement act now changes your system's state function from what it would have been if you had left it alone ( it 'collapses' ). It is also different from what it would be if some other measurement outcome had occurred. The probability weighted mean of the spectrum is called the 'expectation' of the measurement. You can expect what you like, but the actual number gained is for all intents and purposes randomly selected from the possibilities available for that single measurement act.
Returning to 'Quantum mechanics makes NO statement whatsoever as to why a particular dot on the board is chosen.' That's where wave meets particle. It is THE gap in the theory. Or the Universe is actually a random affair propagating into the future though within some general behavioural bounds.
Another mind-boggle is that when you apply QM to the world it is stunningly successful and doesn't look like being beaten for predictive accuracy any time soon.
Mind you I'm not overly disturbed by this. 'Random' is a placeholder for 'who knows' or 'who can say' ? Not a biggie. :-)
Cheers, Mike.
( edit ) Side note : this is why I chuckle at some of the more pretentious presentations & treatments of the search for the Theory Of Everything ( TOE ). All current TOE candidates have QM inside. But inside QM itself is an implicit 'stuffed if I know' !! :-):-)
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Thanks Mike, It's going to
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Thanks Mike,
It's going to take me a few meals to get through this. But I will. And I will come back to your comments from time to time to reinforce what was said. I am thrilled that I can actually ask my questions on these things and have someone answer rather than just trying to read another book or watch another science tv episode.
merle
What is freedom of expression? Without the freedom to offend, it ceases to exist.
— Salman Rushdie
Mike, Enjoyed reading your
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Mike,
Enjoyed reading your learned posts in response to Merle's concerns about the gravitational wave (GW). I was a bit surprised though that your response did not reveal the kind of faith I assume most participants of this project have, namely, that the force of gravity is transmitted through space, over time, by means of a real wave. It would be hard for me to understand why anyone would attach their computer to this project if they didn't believe that or something like that. Anyway its in the spirit of restoring the faith that I offer my comment.
I'm not so sure that quantum mechanics(QM)is the best perspective to have in searching for the elusive GW. Relativity theory is an uncomfortable fit within the framework of the Copenhagen Interpretation and Bohr's Complementarity theory of wave-particle duality. First of all, current understanding of the force of gravity still retains its 'continuous' character. Perhaps this is why a creditable quantum theory of gravity is so hard to come by. Also, the picture of reality we get through the Copenhagen Interpretation won't serve us in our search for the GW. We are searching for a real wave and for me what is real is what our best scientific theories say is real. So until relativity is proven wrong, or is replaced by a theory that does not predict the GW, I will believe that GWs exist EVEN WHEN WE ARE NOT DETECTING THEM. (I think Schrodinger would insist on this.) But most of all, quantum theory is almost exclusively quantitative in its approach to describing reality and for this reason may not be able to describe all relevant qualities of the GW. I too, like Einstein, think that QM is not a complete theory.
Let me explain what I mean by way of a simple example. We known that we can change the current within a circuit by varying the voltage or resistance. A new equilibrium is reached which we can measure at various separate points in the circuit. Ohm's law allows us to predict the new equilibrium. We believe time considerations can be neglected since it could hardly affect the quantity we seek, so we just ignore it. This can give rise to what I like to call the quantitative illusion of action at a distance. Since we can ignore anything not related to our aim and predict the equilibrium outcome, it seems reasonable to suppose that we have a complete understanding of current regulation in the circuit. We may safely ignore such questions as: how did the change in current start, how was it transmitted, and what mechanism determines the new equilibrium? But unless we have answers to these questions, can we really say that we understand how current is regulated in a circuit? Do we really believe there is no real underlying process or that, whatever it is, it's not important to our understanding?
This is the difficulty I see with exclusive use of the Copenhagen interpretation and Schrodinger's equation to frame our understanding of the physical universe. Schrodinger's equation, as you point out, describes the evolution of a wave from one state to the next with a high degree of accuracy. But this encourages the attitude that if we know what happens next, who cares how we got there? In my opinion, this is just the sort of attitude that makes 'action at a distance' seem reasonable, 'spooky' action at a distance as Einstein called it. This is perhaps the sort of problem Einstein saw with the quantitative description favored by Bohr and Heisenberg. But aside from this I think this attitude limits the bounds of legitimate scientific research with professors prompting students not to ask questions about things they cannot observe or detect.
Finally, let me say that Bell's inequalities and Aspect's experiment not withstanding, the 'action at a distance' issue is far from settled and the discovery of a GW would force the scientific community to take a fresh look at the matter.
P.S.
It's obvious from reading your posts that you have a broad background in contemporary theoretical physics, so I'm guessing you're a professional physicist or at least an advanced graduate student. I want to assure you I mean no disrespect to your profession nor am I questioning your expertise with my comment. Science is just a hobby with me and I did sincerely enjoy reading your posts.
RE: It's obvious from
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You could always try looking looking here. :-).
Cheers,
Gary.
Thanks Gary ! :-) Alas
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Thanks Gary ! :-)
Alas Robert I run a decent risk of way looking smarter than I am here. Please preface all my remarks with an implicit As Far As I Know or somesuch. I'll get to reply to your main remarks/content later but for the present beware I am very much a hobbyist, with my 'proper' label of expertise in real life being ... hmmm ... 'pediatrician' is probably the closest stool to legitimately sit me on currently. I have worn many hats within the paddock of medicine over the last 3.5 decades, now that I come to consider it. Anyhows please do speak up and be heard on whatever level, without fear ... let us not be concerned with formality! :-) :-)
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
RE: Mike, Enjoyed reading
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I'm taking the strict impassive approach here, that is the experiment that LIGO et al represents is an inquisition upon reality and thus must be respected above our precepts. I certainly have an expectation ( or what I would wager real money upon ) that GW's are real and their demonstration is near. However for me the ghosts of Michelson & Morley lurk hereabouts. They used interferometry to measure Earth's velocity with regard to an aether. Their famous null result - a well performed inquiry upon the Universe - has been so fruitful, however initially confounding. As indicated earlier in this thread : if there are no GW's then what is the mechanism to 'save the appearances' of conservation of energy ? That would be one of many issues to preserve what we like to think of as a unified and consistent review of reality. So intellectually it would be exceedingly convenient to find GW's .... :-)
Quite right, but the OP having raised the ideas of 'wave' and 'particle' leads to that discussion. Or I thought it might help to go that way. Gulp. :-)
Agreed, one can use a theory and it's notions for predictive utility alone. We don't always have to be minimalist by applying Occam's Razor(s). So you can legitimately retain unmeasurable entities like the wave function for the purpose of cognitive efficiency.
[aside]Actually there is a very common shortcut like that which we use routinely while not necessarily recognising it's status in that regard. It is energy! Yup. To be very rigorous energy - in all of it's forms - is only ever a calculated thing. I could be even nastier and say that conservation of energy is likewise a useful supposition, much like Schrodinger's equation, that permits continuity across our explanations. And we have worked hard to retain it as a principle ie. expand on the ways in which energy may be calculated precisely in order to achieve that retention ! I don't know why you would, because it is such a tremendous simplification, but you could discuss much of physics prior to the Relativities at least ( and successfully predict & measure etc ) without touching the concept of energy at all. Mind you Frank Wilczek ( particle physicist & Nobel Laureate ) has published a book entitled 'The Lightness of Being' where he re-arranges the structure of physical theory - in the sense of re-basing what are the traditional axioms - to give 'energy' the central status and others hence become derived components. But I digress.[/aside]
No argument there either. The EPR discussion was initially a foil in rebutting the Copenhagen crew. It is ironic to say the least that it lead to more questions than it answered, as opposed to a final 'no' statement that was the authors' intent.
Yup, this is what say Lisa Randall and others would claim is an 'effective theory', defined largely by being fit for some purpose of interest. Of course all such theories do have their boundaries - in my opinion too infrequently declared - that disclose the target purpose/context and for that matter the margin/tolerance of fit.
Again I yield to no contest. An excellent related, and very quizzical, example is that one doesn't have to suffer the wave function collapse. You can show, as did Mr Everitt, that there is an alternative & consistent approach to solving Schrodinger's equation. You can literally have your cake and eat it too ! All operator outcomes persist after application/measurement. But that then serves up a massive problem in interpretation ie. where are all of those alternate universes ( in any serious measurable sense ).
Entanglement/coherence is a big challenge for the sub-light speed particle view. My very rough take on this area is that it necessarily implies some type of 'palimpsest' model. A digression : velum was processed calf hide used prior to good paper production. An expensive luxury to say the least ( medieval times here ). The scribes would re-use them by ablating prior markings and over-writing. But on close inspection one could define that previous use, to some degree at least. There is an equivalent word/phrase, which I don't recall, referring to the same sort of thing with paintings on canvases. Another way of expressing this is that there must be legitimate other dimensions that we can't directly measure. By legitimate I mean actually existing not as a convenient model now. So we are ducks upon a pond, as it were, that may deduce the depth below without ever diving. But this is no theory fit for any test as it stands, and certainly not the least bit novel. See 'Warped Passages' by Lisa Randall for a brilliant recent exposition, or Kaluza & Klein last century for that matter.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal