Imagine the famous two slit experiment. In this version we will fire electrons at the slits, one at a time. Put a very accurate spring balance behind each slit and measure the gravitational attraction of the electron as it goes past.
The author then claims, "The description that General Relativity puts forth ... needs to be augmented to include an uncertain position that has a probability distribution to it."
Does that follow? Wouldn't, say, the Pilot Wave Theory avoid the need for GR to change?
Yes, this is my thought as well. It simply does not follow that the two alternatives are a probabilistic stress energy tensor or a violation of the uncertainty principle.
Since quantum mechanics describes electrons as a field and not as a particle with position and momentum, there is always the possibility that an extension to the field or a function of the field itself can generate a classical stress energy tensor.
Yes, but that doesn't solve the problem. That is just another way of rephrasing the problem. A stress-energy tensor is still dependent upon position and strictly speaking is not a thing in itself, but a mathematical description of an thing/effect - in this case a graviton field or equivalent which is associated with the higgs field of a particle in superposition. The result will always be described via a stress-energy tensor, but this is a description of a result, not a cause.
However this works out, we still have to deal with the "position problem" when it comes to describing the gravitational field of a particle.
Also, I don't think we will get very far by trying to attach gravity to QM on the level of probabilities. You will want to connect them on a field level obviously.
The probabilities are jusy a crutch that link the quantum world to our perceptions.
I don't think the author ruled out a field-theoretic description (whether as a quantum field or as a classical field). But using the language of fields and talking e.g. about the precise coupling between gravity and other quantum fields doesn't add anything to the discussion here. The question is whether the gravitational field behaves in a quantum mechanical fashion (and thus allows for superpositions) or not. To ponder this, you don't need fields. It's a completely separate issue.
there are a couple definitions you would need to elaborate on to realise this question fully
by particle physicists usually mean any electromagnetic phenomena that seems to have distinct energy levels and so can refer to any number of things depending on context: photons, electrons, protons, atoms(o)
as for interact, what do you mean by this? would you consider entanglement an 'interaction'? the idea of a wavefunction is basically that every particle is 'interacting' with every other particle in existence in every direction with potential of collisions being discernible by the probabilities of the particle's position being spread out ad inifinitum
according to relativity light has a constant speed, meaning it is always moving at 'c'
since the photon is moving it has energy and though it has a 'rest' mass of 0 it is without a rest frame because it is always moving at that constant speed and so always has some measurable mass
because of this even in a universe with only a single photon without anything to interact with the photon would still affect spacetime
if you remove the 'only' from your question then the answer is an emphatic yes because you yourself are a collection of 'particles' 'interacting' and you are affecting spacetime
> by particle physicists usually mean .. photons, electrons, protons, atoms(o)
I meant pretty much anything that can be described by wave function evolving according to Schrodinger equation.
> as for interact, what do you mean by this?
Exchange of energy through any of 3 physical forces (not gravity). So not entanglement.
Single photon universe would never be observed so it would have wave function but never have specific location so according to my idea it would not affect spacetime.
> The description that General Relativity puts forth ... needs to be augmented to include an uncertain position that has a probability distribution to it.
i am sorry but 'needs' is too strong here
quantisation(o) was established before, necessarily so, probability was introduced to explain the behaviour of electromagnetic phenomena
to claim that probability is necessary for quantisation seems to have it reversed
the current understanding is both unknown whether gravity is quantised but also whether probability is necessary to describe quantum behaviour
with current understanding the only thing one can say with certainty is that requiring probability is a result of the math used to best model quantum behaviour of electromagnetic phenomena, namely fourier analysis(i)
Sorry for asking this in here, but since the double slit experiment is mentioned, I have a question.
Is the wave formed by light a 2d wave, like waves on the surface of the water?
And if so, then if we turn the slits sideways, why does the interference pattern also turns sideways? it shouldn't turn sideways if light is a 2d wave.
My apologies for the offtopic question, but I couldn't find any answer about this anywhere.
Light acts like a 2D wave when it's linearly polarised. But it can also have circular polarisation - which rotates - or some mix of polarisations.
If you put a vertical polariser in front of one slit and a horizontal polariser in front of the other slit, the usual pattern of fringes disappears. So polarisation does matter for the experiment.
But I'd strongly suggest not thinking of light in wave and/or particle terms. In Quantum Field Theory everything is made of fields, which are more like carriers of probability which strongly hint at some weird non-local properties, than a nice smooth lake surface waiting for some ripples.
If you try to apply physical intuition to QM it soon stops making any sense at all. So IMO it's best not to start there.
If we can't make the analogy between the surface of water and light, then how come the double slit experiment shows us that the interference pattern is due to the wavy nature of light?
Because a wave is a more general phenomenon than what happens on the surface of water, and waves of all kind result in interference patterns. Also, waves in the ocean certainly aren't two dimensional either, the surface "wave" just a visible manifestation of a larger system.
But the polarisation of light demonstrates more quantum effects. Put two polarising filters in front of a light at 90 degrees to each other and no light gets through them both; yet add a third filter in between at 45 degrees angle to each, and now half of the light gets through all three filters! Adding extra filters can make them let more light through, not less...
Good question. The pattern will indeed turn sideways.
1. There is nothing deep about the shape of the slit. You can do the "double-slit" experiment with "double-pinhole" or "double-weirdshapes" and you will get the same behavior, just that the math will be different.
2. In fact, there is a simpler experiment you can do which gives the same qualitative results, but in which the shape of the wave is much less relevant. You can split a single photon into two fiber cables using a beamsplitter, then interfere the light in those cables using another beamsplitter. The good thing about this is that all the operations in this setup are linear, because light is not lost anywhere. In a double-slit experiment, light that falls outside the slits gets blocked and so the operations are non-linear and you have to worry about the shape of the slits and wave a lot more.
3. I am not quite sure which two dimensions you mean, when you say 2d wave. There are two axes in the plane of the slits (longitudinal) and another axis perpendicular to this plane (transverse). The wave of light is in fact 3D, but lets simplify. If its 2D in the longitudinal axes, then obviously the shape/orientation of the slits matter. Imagine putting a rainbow colored piece of paper against the slits. Depending on the orientation of the slits, different colors will make contact with the slits. If its 2D in transverse+one longitudinal axis then it still matters. Imagine taking a stack of identical rainbow colored paper and put it edge on against the slits. If you rotate the slits, obviously the colors making contact with the slits will change. Hence, the interference pattern changes again.
1. Yes, light is always 3D but the description in popular science is always simplified. Also experiments usually measure along a line across the screen and don't build up a 2D pattern on the screen that you usually see in popular science. For instance Fig 4. here [1] .
2. Because the light does not diffract up and down too much, only horizontally. So, for instance, the light emerging from the middle of the left slit stays at the middle level and does not interfere with the light emerging from the bottom of the right slit.
Imagine looking somewhere on the screen at middle height where the path lengths are so that its a dark point. The light here is coming from the middle of both slits. Now move down a bit. The light here is coming from the bottom of the two slits here, and the path lengths are still the same. So you still get a dark point. I hope this makes it clear.
The "direction" of the wave affects polarization, which is critical for LCDs working. But that's not relevant to the double slit experiment, because the slits and spacing are larger than the waves. The double slit experiment relies on diffraction, the tendency of the waves to bend round corners.
"General Relativity describes gravity perfectly everywhere we've ever looked. From the smallest-scale attractions we've ever measured in a laboratory to the expansion and curvature of space due to Earth, the Sun, black holes, galaxies, or the entire Universe, our observations and measurements have never deviated from what we've observed. "
So correct me if I'm wrong, but the rotation of galaxies completely defies even Newtonian principles, right?
So we invented concepts of Dark Matter / Dark Energy as a placeholder, crossing our fingers that we're right on that?
Imagine a china mug full of water. You can see the mug and the water being held in by the mug.
Now imagine a glass of water. The purest most transparent glass ever, with an identical refraction index as the water. You can't see the glass. You just see the water being held together by something. You don't know the glass exists.
You 'invent' the glass to explain the behaviour of the water, seeing as you know the how the mug affects the water.
The glass is testable though and would quickly be found. Dark matter and dark energy are assumed to exist with no experimental observations occurring. Every experiment has so far failed to show the existence of said entities.
One possibility is that we do not have any way to find said entities with any means at our disposal. Another possibility is that they do not exist (just a figment of imagination) and that the theories requiring them are wrong. In that case, one should be looking for other theories that might be a more capable explanation.
The question here is to determine when or whether we should stop looking for these entities and maybe move onto another model/theory.
The basic assumption of all gravity based theories and models is that the universe is electrically neutral everywhere and that magnetic and electric fields have no possible influence at stellar, interstellar, galactic and intergalactic distances. Whether this assumption is true or not is difficult to gauge since we only have visual observations (at all sorts of frequencies) and cannot actually get out there to make the required measurements.
So we have to fall back to what we think is reasonable and work from there.
> The basic assumption of all gravity based theories and models is that the universe is electrically neutral everywhere and that magnetic and electric fields have no possible influence at stellar, interstellar, galactic and intergalactic distances
This is impressively inaccurate: plasmas (charged and magnetic fluids) are basically the entirety of stellar evolution and the main part of everything up to galaxy evolution, so we have pretty good limits on the magnetic fields out in the universe.
There is also direct measurements of magnetic fields integrated along the line of sight out to cosmological distances, and of course every spectra ever taken has measured the ionization level of the luminous gas.
I agree. Yet the models assume that gravity is the only influence for the motion of the galaxies, etc. We can see evidence of other phenomena but....
I have had this discussion with trained working physicists and the general reaction has been that these phenomena are completely insignificant in relation to stellar, interstellar, galactic and intergalactic motion. So where do we stand? If the orders of magnitude difference in strength between electric and magnetic fields and the strength of gravity is over 35. What kinds of effects do we expect with these kinds of differences? Especially when we are looking at plasmas and all sorts of ionisation.
I don't know, but it does lead to intriguing questions.
> Dark matter is also required to make the predictions of primordial nucleosynthesis correct...
Could you expand on this a bit? I've seen that twice in the last week, but never heard it before. Can you give me a pointer to what you're talking about here?
The rotation of galaxies defies any solely gravity based model, irrespective of whether or not we use General Relativity, Newtonian principles or other gravity models. The addition of entities to some of these models to bring about compliance of those models with observation has not yet led to any experimental verification of such entities.
There are models of gravitation that are based on classical electromagnetics, wherein, gravity is a residual by-product of the electromagnetic interaction between the components of atoms. The models appear to be of the correct order of magnitude for the size of the forces.
However, like a lot of models that have been developed in the last 100 years, there does not appear to be any traction to investigate these models as they are not the commonly ascribed-to models. So we are unable to see if these models produce better predictions for the experiments that are being done around the world.
Please give us the CMB power spectrum with your favourite MOND theory before continuing on your tirade about how those theories are neglected without basis.
"We do not know beforehand where fundamental insights will arise from about our mysterious and lovely solar system. The history of our study of our solar system shows clear that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources." - Carl Sagan
Quoting what Sagan said about new ideas is a pitiful excuse for not providing answers to questions about what the ideas entail.
LambdaCDM gives us both rotation curves and structure formation (in particular the angular power spectrum to something like 23 peaks), so any new theory needs to reach this baseline.
You make the mistake of thinking that it has to be a MOND theory, I wasn't even thinking of MONDs. There are other models that do not assume that gravity is the only significant force at such levels. Whether these other models can match up to the observations is what we need to investigate. The point here is that none of the current crop of theories matches what we see at all the different levels at which we make observations. This is not a problem per se but an intriguing opportunity to do further investigations into what could be better explanations.
All I am saying is that the assumption of gravity being the only significant force (whatever gravity may be) has only led in the standard models, so far, to a proposal of dark matter for which all experiments designed to find it have failed. We have got to a position where there is a big discrepancy between the evidence that is being collected and what theory is predicting. There are plenty of questions being raised across the board about what the data collected actually means.
I am simply putting forward that there may be a possibility that General Relativity has reached a limit of usefulness and may need to be superseded.
There may be a model that gives an explanation of what we see without resorting to adding entities for which we have not received any confirmation by experiment. What that is, I don't know. I don't get paid to do that kind of research.
If we can't find the experimental evidence to support an idea that theory requires, maybe we need to look elsewhere, including into alternative models and theories.
Unless we are willing to look at different ideas and test them appropriately and rigorously when we come to significant roadblocks, we are then stuck in patterns that aren't helpful.
This is the study of the universe we are looking at, at both the very small and the very large and everything in between.
We make many assumptions in developing our theories and models, but if some of those are not quite the reality then our models can and do give results that seem okay, but in the detail are not.
Mathematical models are always idealised models. They do not take into consideration all that exists in reality. For many purposes, that is acceptable - it becomes a case of close enough is good enough. But, if you take that same model into a physical situation where the idealisations used are not matching reality, then that model will give your incorrect results. For example, in the main you may be able to assume that some feature of reality is of very minor significance, but if you change to a place where that feature is now significant, your mathematics breaks down. You have to change your model or even develop a complete new theory by which you do your investigations.
This kind of thing should be standard practice.
I'll leave you with a final thought. At about the time that Gell-Mann was working on his ideas about quarks, there was another man working on another model to explain what was being seen at the sub-atomic level. Now, this man was not a theoretical scientist but he also came up with an idea of a 1/3 charged particle. His purpose for working on the theory was purely for his own interest (he was dissatisfied with the theory and models around at the time). One he had finished his work, he put it aside and went on with his quite successful life. One of his innate abilities was that he had an eidetic memory and when quizzed could described anything on any page of his 6000+ pages of documents.
I received some of his papers years ago from someone who knew him and had obtained all of those papers. What I found intriguing was that part of the model he developed gave a much better and more easily calculable way of determining the binding energy of any nucleus (from H to Fe at least). He made it quite clear that the model was just that - a model and that one should not expect reality to actually match the model. In another part of the theoretical work he did, he made a slight modification to the electric field equation to include a Lorenz transformation which did away with the need for the strong nuclear force.
Since then, I have come across still another modification of the electric field equation (from a completely different location) which gives rise to a residual force (always attractive) and on the same order of magnitude as gravity.
Now, one of these modifications works on the very small and one works on the very large. Do they have any practical significance? I don't know, but unless there is interest in looking at whether they are capable of explaining what we see, we will never actually know. They may be dead-ends, but they may also open up completely new avenues for investigation.
What I am saying is that there are major problems in the current crop of explanations that are being touted as the "truth". Science is about developing theories and models by which we can understand the universe around us. When we start to believe that they are "true", we then have a very hard time accepting evidence that says they are not at all accurate.
Whether the "Electric Universe" or any other model is capable or not of explaining what we see is for research efforts.
What bemuses me is the apparent inability of highly trained scientists to think outside the box so to speak. They appear to be happy with their mathematical incantations (I know the word is provocative) as being the "truth" of reality. Science is not about "truth", it is about providing functional ways to understand and manipulate the universe around us in an organised logical way. If you want "truth", go become a philosopher or theologian.
But come on, all mathematics is a map by which we try to understand the processes going on around us. In the main they provide a way of logically looking at the universe around us, but they are approximate and fail in the very fine detail. Otherwise, we would not have this incredible incompatibility between how we describe the very small and how we describe the very large.
There is a strong unwillingness amongst many of those who propagate the current crop of widely accepted theories to give any credence that their theories and models may be fundamentally wrong.
We do not learn the lessons of the past, so we repeat the same mistakes. So what if a model does not accord with consensus? The Nobel Prise has been awarded to people for discoveries in fields where those people faced great ridicule because of what they discovered was against the consensus model and theory at the time of discovery.
If our theories and models have gaping holes, let us investigate alternatives that might not have those gaping holes.
One of my goals at the moment is trying to see if the original source material is available. As far as I know they were sent to a Canadian archive, possibly civilian, possibly military just before or just after the death of the person I got my copies from. I am interested in seeing the original papers to try and get a handle on what was being proposed.
The copies I have are partially edited and incomplete, which is why I would like to get access to the source material. I am just having difficulty trying to track down where this stuff is. As a consequence, I am having to search through all of my off-line archives for any relevant information. After 20 or more years, that is a lot of material to go through.
As I was saying to someone in recent days, I have between 500 and 1500 papers and books that I want to read and these are just the ones I currently have on-line. just looking for any one paper that I am interested can take quite a while to find. Let alone all the off-line papers and books that I am interested in reading.
So, when I do get access to this material, I will be trying to get it online to the general community even if it is only scans.
Do you happen to know if any of this mysterious researcher's papers might be on the arxiv?
And have you looked into automated digitizing machines for your collection? The University of Tokyo seems to have a pretty good one: https://www.youtube.com/watch?v=03ccxwNssmo :)
No. Both the original author and the gentleman providing exposure were both dead before arxiv was a thing. Unless, one of the various scientists who were involved in looking at the subject matter has put it in an available spot, I don't think that there are any publicly available sources. Though, I can try and see if the Wayback machine has any copies. That will require me looking at my off-line records though and that will take some time.
Hey, I am also very interested in these documents. When I wanted to scan some of my university courses and other stuff for preservation, I just bought a second hand printer/scanner combination, and paid attention to choose a model with ADF (automatic document feeder), occasionally it jams and I have to restart a batch, but it goes quicker than you think even if the ADF only supports ~30 pages or so.
Could you at least mention the name of the original author? What makes you think the notes were sent to an archive?
My understanding (limited, admittedly) is that there are a number of phenomenon that dark matter explains very well, galactic rotation among them. Alternative theories of gravity that explain galactic rotation often don't fit all the others very well.
Dark matter doesn't 'explain' being itself a fudge factor. We give it a name to resolve observations that do not fit our models. We have a strong belief in gravitational laws and theory that we take it as fixed and make the rest fit as needed. Not having an alternate theory of gravitation that is as good makes this reasonable.
It's far more than a simple fudge factor. It says that there is matter with mass, affecting other matter via gravity, but no other interactions seem possible with it. That is a sound, almost complete theory with some unknowns around why it doesn't otherwise interact, what it actually is.
Dark matter also explains certain gravitational lensing phenomenon, aspects of the CMB, from mass location during galactic collisions (and more).
Other theories can possibly explain one or some of those observations, but nothing does a good job (or a simple one) of explaining them all.
Dark matter is real enough to make verifiable predictions in other places. Other theories don't.
When I try to picture the “smeared out” gravitational field of a single “smeared out” quantum particle my head hurts. Try to nail down its position by hitting it with a photon and you thereby increase its momentum and thus relative mass and gravitational field... plus all those gravitons have energies of their own and therefore associated graviton-mediated gravitational fields... it’s a heroic mess.
You don't increase its momentum. You increase the uncertainty in the momentum. So if initially position was 5 +- 3 and momentum was 10 +- 2, then afterwards, you might know that position is 6 +- 1, and momentum is 10 +- 4.
The rest of your train of thought doesn't follow after this refutation.
> You set up a photodetector around each slit, and measure when a particle passes through it.
[...No interference happens...]
> This is weird!
No, it's not. You made that particle's wave function collide with the huge wave function of a photodetector, of course it's going mess up the wave of the particle itself.
> Does the gravitational field always go primarily through one slit or the other? And does the act of observing (or not observing) change the gravitational field? And if so, how?
The Copenhagen interpretation is really throwing a wrench into our understanding of physics.
Imagine the famous two slit experiment. In this version we will fire electrons at the slits, one at a time. Put a very accurate spring balance behind each slit and measure the gravitational attraction of the electron as it goes past.
The author then claims, "The description that General Relativity puts forth ... needs to be augmented to include an uncertain position that has a probability distribution to it."
Does that follow? Wouldn't, say, the Pilot Wave Theory avoid the need for GR to change?