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Thread: What do you think is mainstream in cosmology?

  1. #1

    What do you think is mainstream in cosmology?

    What do you think is mainstream in cosmology? I seem to have some difficulties with this. Not so much with stars and planets and matters subject to observational fact, but to the theoretical side of things. I'll read about something in what looks like an excellent source, then I'll read a totally different theory or explanation somewhere else, and then hear people saying this is the mainstream view.

    I had a hint of that the other day when I was reading a blog post on True Facts About Cosmology (or, Misconceptions Skewered). I read this: "When you take gravity into account, the total energy of any closed universe is exactly zero". However when you take a look at the Einstein digital papers, you can find Einstein saying "the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy". That means gravitational field energy is positive. And surely if you have a universe consisting of two massive bodies which fall towards one another, they don't disappear when they meet. Do you think the negative-energy gravitational field is mainstream? Or the zero-energy universe?

    Another example is equivalence principle. You can read that "being on the surface of the Earth is equivalent to being inside a spaceship (far from any sources of gravity) that is being accelerated by its engines". The room has to be small enough so that tidal forces may be neglected. But as for how small, note that in Fundamental ideas and methods of the theory of relativity Einstein said special relativity is only valid "in the infinitesimal". Your room has to be an infinitesimal room for the equivalence principle to exactly apply. Which is presumably why on pages ix and x in his 1960 preface to relativity: the general theory, John Synge said the equivalence principle performed the essential office of midwife at the birth of general relativity, but should "be buried with appropriate honours". And yet people say that if you can disprove the principle of equivalence, you disprove general relativity. Do you think that's the mainstream view?

    A further example is gravitational redshift. Take a look at page 149 of Relativity, the Special and General Theory where Einstein said "an atom absorbs or emits light at a frequency which is dependent on the potential of the gravitational field in which it is situated". So a radioactive 57Fe atom in the basement will emit a gamma photon at a lower frequency than an atom on the roof. The gamma photon doesn't lose energy as it ascends from the basement to the roof. And yet as far as I can tell, that seems to be the mainstream view. Is it your view?

    There's lots more examples like this. Who wants to talk about this stuff? Feel free to suggest other topics. A few that spring to mind are Hawking radiation, the information paradox, firewalls, inflation, wormholes, and WIMPs. I'd say such things are considered to be mainstream, but we don't have any actual evidence for them. Other things aren't so black and white, such as point singularities, the waterfall analogy, and time travel via CTCs. It might be interesting if we could identify a topic that you all think of as being rock-solid mainstream cosmology, but which I think is bunk. Then I could start an Against the Mainstream thread on it. A quality thread, with references. Not just some wild idea with no foundational support.

    Moderators, feel free to move this thread into the ATM forum. I imagine this discussion could easily turn into the sort of thing that you think should be in there.

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    Quote Originally Posted by The Physics Detective View Post
    Another example is equivalence principle. You can read that "being on the surface of the Earth is equivalent to being inside a spaceship (far from any sources of gravity) that is being accelerated by its engines". The room has to be small enough so that tidal forces may be neglected. But as for how small, note that in Fundamental ideas and methods of the theory of relativity Einstein said special relativity is only valid "in the infinitesimal". Your room has to be an infinitesimal room for the equivalence principle to exactly apply. Which is presumably why on pages ix and x in his 1960 preface to relativity: the general theory, John Synge said the equivalence principle performed the essential office of midwife at the birth of general relativity, but should "be buried with appropriate honours". And yet people say that if you can disprove the principle of equivalence, you disprove general relativity. Do you think that's the mainstream view?
    Not sure what your point is here. The equivalence principle is confirmed by the fact that GR works, so it is certainly valid.

    Is your objection that the two are only exactly the same at a single location because gravity falls off with distance?

    A further example is gravitational redshift. Take a look at page 149 of Relativity, the Special and General Theory where Einstein said "an atom absorbs or emits light at a frequency which is dependent on the potential of the gravitational field in which it is situated". So a radioactive 57Fe atom in the basement will emit a gamma photon at a lower frequency than an atom on the roof. The gamma photon doesn't lose energy as it ascends from the basement to the roof. And yet as far as I can tell, that seems to be the mainstream view. Is it your view?
    I seem to remember a thread about this (but it might have been on a different forum). As far as I can tell, these are just two different descriptions of the same thing. You can consider the photon was emitted with a different energy OR that it loses energy. What you measure is the same in both cases, so how could you distinguish them?

    There's lots more examples like this.
    You mentioned the possibility of the universe being infinite in another thread, and suggested that there was an inconsistency there. It would have been off topic, but I wanted to point out that you were comparing two different things: one was a fact about the observable universe, the other was about the whole universe.

  3. #3
    Quote Originally Posted by Strange View Post
    Not sure what your point is here. The equivalence principle is confirmed by the fact that GR works, so it is certainly valid.
    I think GR is one of the best-tested theory we've got. See The Confrontation between General Relativity and Experiment by Clifford M Will. But also see See Kevin Brown‘s mathspages article on the many principles of equivalence. He says this "the modern statement of the strong equivalence principle, of the assertion that the laws of physics are the same for all frames of reference (i.e. independent of velocity) is also conceptually quite distinct from the original meaning of Einstein’s equivalence principle". Then see the Einstein equivalence principle on Wikipedia. It says "the outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime". That isn’t what Einstein said in 1907 about falling off a roof and all bodies falling at the same rate. And yet we get papers like SpaceTime Mission: Clock Test of Relativity at Four Solar Radii. They suggested that if they measure the fine structure constant to be different close to the Sun, GR is wrong. I say it isn't. I would say it's the "Einstein" equivalence principle that's wrong, but Einstein wasn't the author of it.

    Quote Originally Posted by Strange View Post
    Is your objection that the two are only exactly the same at a single location because gravity falls off with distance?
    No. My objection is that The Einstein Equivalence Principle is not really Einstein's equivalence principle, and shouldn't be seen as a central tenet of GR. Wikipedia says this: "The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime. I consider myself to be a "relativist", and I don't consider this to be true. I think we have evidence that it isn't.

    Quote Originally Posted by Strange View Post
    I seem to remember a thread about this (but it might have been on a different forum). As far as I can tell, these are just two different descriptions of the same thing. You can consider the photon was emitted with a different energy OR that it loses energy. What you measure is the same in both cases, so how could you distinguish them?
    By paying careful attention to what Einstein said and understanding conservation of energy. I know that when I move towards a photon in free space I measure it to be blue-shifted because I changed. The photon didn't. In similar vein I understand the mass deficit, and that if I lift you up I do work on you. I add energy to you. So when you're at a higher elevation and you measure the ascending photon to be redshifted, it's because you changed. Not the photon. I know of no mechanism by which a photon loses energy all on its own. I do not believe in tired light. See the Tamar Davis Scientific American article Is the Universe leaking energy?

    Quote Originally Posted by Strange View Post
    You mentioned the possibility of the universe being infinite in another thread, and suggested that there was an inconsistency there. It would have been off topic, but I wanted to point out that you were comparing two different things: one was a fact about the observable universe, the other was about the whole universe.
    I remember when the mainstream view was that the whole universe is finite. After WMAP there was an unannounced shift, wherein the mainstream view changed such that the observable universe was finite, and the whole universe was infinite. I don't buy it.

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    Be Skeptical (very skeptical) !

    Quote Originally Posted by The Physics Detective View Post

    (snip)

    [url=https://www.preposterousuniverse.com/blog/2019/01/12/true-facts-about-cosmology-or-misconceptions-skewered/]

    (snip)
    The answer to your question is above. Anytime anyone starts talking about 'true facts', you can recognize immediately that they probably don't know what they are talking about. Facts are true by definition.

    Also, be very careful about cherry picking your sources. The fact that it is on the Internet is meaningless. I notice this is not in a legitimate peer reviewed poblication.

    See below.
    I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.

    "Mainstream isn’t a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik

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    Quote Originally Posted by The Physics Detective View Post
    But also see See Kevin Brown‘s mathspages article on the many principles of equivalence. He says this "the modern statement of the strong equivalence principle, of the assertion that the laws of physics are the same for all frames of reference (i.e. independent of velocity) is also conceptually quite distinct from the original meaning of Einstein’s equivalence principle".
    So what? That doesn't change the science in any way. There are dozens of different interpretations of quantum theory. They all describe the same theory.

    Then see the Einstein equivalence principle on Wikipedia. It says "the outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime".
    That's just another way of saying the same thing - for the particular case of no gravity being indistinguishable from free fall. Again, so what?

    That isn’t what Einstein said in 1907 about falling off a roof and all bodies falling at the same rate.
    Not sure which bit of that you are referring to but as far as I can tell, he is saying exactly the same thing: "then there is no objective reason for the observer to consider himself as falling in a gravitational field. To the contrary, he has every right to consider himself in a state of rest and his vi- cinity as free of fields as far as gravitation is concerned." (But I have always found Einstein's writings on the subject to be rather hard work.)

    Wikipedia says this: "The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime. I consider myself to be a "relativist", and I don't consider this to be true. I think we have evidence that it isn't.
    Then you will need to start a thread in Against the Mainstream and present that evidence.

    By paying careful attention to what Einstein said and understanding conservation of energy. I know that when I move towards a photon in free space I measure it to be blue-shifted because I changed. The photon didn't. In similar vein I understand the mass deficit, and that if I lift you up I do work on you. I add energy to you. So when you're at a higher elevation and you measure the ascending photon to be redshifted, it's because you changed. Not the photon. I know of no mechanism by which a photon loses energy all on its own.
    Fine. That is your preferred interpretation. But unless you can suggest an experiment that distinguishes the two descriptions (and I don't think you can) then it doesn't matter.

    I do not believe in tired light. See the Tamar Davis Scientific American article Is the Universe leaking energy?
    That appears to be a non sequitur.

    I remember when the mainstream view was that the whole universe is finite.
    When was that? Newton proved it must be infinite (in a world where Newtonian gravity applies). GR shows that it can be either finite or infinite.

    After WMAP there was an unannounced shift, wherein the mainstream view changed such that the observable universe was finite, and the whole universe was infinite. I don't buy it.
    Citation needed. The possibility that the universe could be infinite has been around as long as I can remember (which is quite a long time!)

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    Quote Originally Posted by John Mendenhall View Post
    The answer to your question is above. Anytime anyone starts talking about 'true facts', you can recognize immediately that they probably don't know what they are talking about. Facts are true by definition.

    Also, be very careful about cherry picking your sources. The fact that it is on the Internet is meaningless. I notice this is not in a legitimate peer reviewed poblication.

    See below.
    I would say that Sean Carroll is a pretty reputable source. And I cannot see anything contentious on that page. (Even if I might, in some contexts, dispute the meaning of "fact".)

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    Quote Originally Posted by The Physics Detective View Post
    By paying careful attention to what Einstein said and understanding conservation of energy. I know that when I move towards a photon in free space I measure it to be blue-shifted because I changed. The photon didn't. In similar vein I understand the mass deficit, and that if I lift you up I do work on you. I add energy to you. So when you're at a higher elevation and you measure the ascending photon to be redshifted, it's because you changed. Not the photon. I know of no mechanism by which a photon loses energy all on its own. I do not believe in tired light. See the Tamar Davis Scientific American article Is the Universe leaking energy?
    If you understand conservation of energy you'll know that it is a local thing, at best, in GR. Energy is not an invariant - it is a pseudotensor and hence its measured value is often path dependent.

    Quote Originally Posted by The Physics Detective View Post
    I remember when the mainstream view was that the whole universe is finite. After WMAP there was an unannounced shift, wherein the mainstream view changed such that the observable universe was finite, and the whole universe was infinite. I don't buy it.
    When was this? Because I was definitely taught, before WMAP, exactly what I still see being taught today as 'mainstream'. The universe could be finite or infinite - we don't know. All we do know are some limits, based on the current model, to how small it can be. Don't mix popular science or views expressed in interviews with what the model says. The latter is the 'mainstream'.

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    Quote Originally Posted by The Physics Detective View Post
    I'll read about something in what looks like an excellent source, then I'll read a totally different theory or explanation somewhere else, and then hear people saying this is the mainstream view.
    The problem is that "the mainstream view" is not always a single monolithic entity when you get to the frontier of any field. This is nothing unusual-- we often like to imagine we live in a world of black and white, but all we have to do is look to be introduced to the color gray. I'm sure this holds in any field-- if you ask a group of biologists what is "mainstream" about Darwinian evolution, you will find very good agreement about topics well away from the current frontier, and a whole lot of disagreement by the time you get to the frontier. Frontiers are always gray.

    Then there is also the issue, mentioned above, of the difference between a theory and an interpretation of a theory. One can say that two theories are the same if they make all the same predictions, even if they are interpreted in very different ways. For example, there is the theory of Newtonian mechanics, where we have force F producing acceleration a=F/m, and then there is Lagrangian mechanics, where we have a scalar function (the "action") that nature somehow strives to minimize. These are the same theories, but they make completely different sounding claims about what is the cause an effect-- Newton says forces cause acceleration, Lagrange says forces are a kind of make believe ramification of the need to minimize action. Then you have quantum mechanics, which also makes the same predictions as Newtonian mechanics on the macro scale, but has wave functions and complex amplitudes (and does differ on the micro scale, but it could still have been the way we describe macro phenomena in Newton's day had we the mathematics then).

    So the bottom line is, we have to recognize that even experts disagree when you get to the frontiers of their fields (some experts think the disagreements between quantum theory and GR must be resolved by a theory of quantum gravity, others think it must be resolved by a new quantum theory). So the concept of "mainstream" becomes gray there, not black and white. And two experts might create all the same predictions using completely different sounding models about what is causing those predictions to hold, so what is "mainstream" can involve multiple possibilities.
    I read this: "When you take gravity into account, the total energy of any closed universe is exactly zero".
    This requires a special definition of energy that is not necessarily widely accepted. Many would say that GR does not support a global concept of energy in general, but in special situations it might be useful to define some special version of energy that has the property of being zero. Energy is not so much a thing as it is a calculational tool, a fact that is evident any time we invoke Newtonian gravity to use a change in gravitational potential energy mgh to calculate a change in kinetic energy when we drop something through distance h-- the result holds regardless of where we take the zero of the gravitational potential, so it holds regardless of what we think the energy there "really is." And in quantum mechanics, you can shift the complex phase of the total wavefunction of any closed system by any amount you like, and it will have no observable consequences, so we can say there is no "actual" wavefunction of a system, even though it might be mainstream to imagine that the wavefunction is a kind of "thing" that takes on actual values of its amplitudes, similar to energy.
    The room has to be small enough so that tidal forces may be neglected. But as for how small, note that in Fundamental ideas and methods of the theory of relativity Einstein said special relativity is only valid "in the infinitesimal".
    That depends on the meaning of the word "valid", which is not a well defined term in mainstream physics. I would be inclined to define "valid" as meaning "gives predictions that agree at some given desired level of accuracy", since I can't think of any other scientifically valid meaning of the term valid. Yet your source clearly takes the meaning "is exactly true," which is not a scientifically useful meaning of anything. So I don't think that source is correct, but it doesn't mean it's not mainstream-- as long as you take their rather problematic meaning of "valid." So these are the kinds of gray areas I'm talking about.
    A further example is gravitational redshift.
    This issue is more like the question of interpretation. Consider any situation where you have a mundane Doppler shift of light in a vacuum. These situations don't really even require relativity if the speeds are not large, because you get a similar expression, to a good level of accuracy at low speeds, for the Doppler shift of sound without any relativity. But where you see the big difference is when you ask, "when did the Doppler shift occur?" For sound, if the source is moving through the air, the Doppler shift occurs when the sound is emitted, and if the receiver is moving through air, it occurs when the sound is heard (or any combination thereof). But for light, there is no "air" to resolve the issue, so you cannot say when the Doppler shift occurred. That's just what you get, you get an observed Doppler shift with no way to know when it happened, so you can interpret when it happened however you like. In practice, the interpretation you use is determined by whatever coordinate system you choose to make the calculation. So the answer to "what happened" is basically "it depends on the coordinates you use to say what happened." That's a perfectly mainstream state of affairs, and it's just what is going on with the question of when gravitational redshifts happen, but it might make experts sound like they are disagreeing when in fact they are merely using different coordinate language.

    This exposes a key "gray area" of physics: language. Einstein worked hard to make the predictions of relativity coordinate independent, because he strongly believed that the laws of physics need not choose any particular coordinates. He succeeded famously, but the irony of that success is that language is already a kind of coordinate system. Hence, if the laws of physics must be coordinate independent, they can never be translated into everyday language-- as the latter does not obey the rule of making those laws language independent. Only the equations can be built to be invariant, not the language we use to interpret the equations. So your question is actually alluding to a very fundamental problem of physics-- we would like to be able to have more than just predictive equations, we want lessons and concepts and understanding. But the latter will never be the same as the former, as the former can be expressed in an invariant form that depends on nothing that has anything to do with the person using them, and the latter quite obviously cannot be expressed that way. What is mainstream when it comes to the equations is normally quite black-and-white, but what they are telling us is generally rather gray.
    Last edited by Ken G; 2019-Jan-22 at 01:09 PM.

  9. #9
    Quote Originally Posted by John Mendenhall View Post
    The answer to your question is above. Anytime anyone starts talking about 'true facts', you can recognize immediately that they probably don't know what they are talking about. Facts are true by definition. Also, be very careful about cherry picking your sources. The fact that it is on the Internet is meaningless. I notice this is not in a legitimate peer reviewed publication.
    I don't mind the use of the phrase "true facts". As for the source, Sussklind's The World as a Hologram was in a legitimate peer-reviewed publication, and I think it's pseudoscience tosh. I hope you guys don't say any criticism of the holographic universe has to be in the ATM forum.
    Last edited by The Physics Detective; 2019-Jan-22 at 02:53 PM.

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    Quote Originally Posted by The Physics Detective View Post
    As for the source, Sussklind's The World as a Hologram was in a legitimate peer-reviewed publication, and I think it's pseudoscience tosh.
    Your link doesn't work: https://arxiv.org/abs/hep-th/9409089

    Perhaps you could point out the errors in this paper, rather than just saying you think it "tosh". If not, why should we take your opinions seriously?

  11. #11
    Quote Originally Posted by Strange View Post
    So what? That doesn't change the science in any way. There are dozens of different interpretations of quantum theory. They all describe the same theory.
    It's like Ken Brown said. The modern statement of the strong equivalence principle, of the assertion that the laws of physics are the same for all frames of reference (i.e. independent of velocity) is also conceptually quite distinct from the original meaning of Einstein’s equivalence principle.

    Quote Originally Posted by Strange View Post
    That's just another way of saying the same thing - for the particular case of no gravity being indistinguishable from free fall. Again, so what?
    It isn't true. If you're in free fall you'll eventually see the fine structure constant changing. If you're in gravity-free space you won't.

    Quote Originally Posted by Strange View Post
    Not sure which bit of that you are referring to but as far as I can tell, he is saying exactly the same thing: "then there is no objective reason for the observer to consider himself as falling in a gravitational field. To the contrary, he has every right to consider himself in a state of rest and his vicinity as free of fields as far as gravitation is concerned".
    It isn't exactly the same. There's been a drift. What's now portrayed as Einstein's equivalence principle is actually the cosmological principle. That isn't based on scientific evidence. It's like saying I see trees in all directions, ergo everybody else does.

    Quote Originally Posted by Strange View Post
    Then you will need to start a thread in Against the Mainstream and present that evidence.
    Maybe I will. The evidence is gamma ray bursts.

    Quote Originally Posted by Strange View Post
    Fine. That is your preferred interpretation. But unless you can suggest an experiment that distinguishes the two descriptions (and I don't think you can) then it doesn't matter.
    It matters. Understanding matters. As for an experiment, a gedankenexperiment will have to do for now. Send a 511keV photon into a black hole. By how much does the black hole mass increase? Is it 511keV/c², or something else? Drop a 511keV electron into a black hole. By how much does the black hole mass increase? Is it 511keV/c², or something else. I know of no perpetual-motion machines. I know of no example of the non-conservation of energy. In my view, conservation of energy is mainstream.

    Quote Originally Posted by Strange View Post
    That appears to be a non sequitur.
    It isn't. The ascending photon doesn't lose any energy, and nor does the CMBR photon. That's Tamara Davis saying that, and I think she's right.

    Quote Originally Posted by Strange View Post
    When was that? Newton proved it must be infinite (in a world where Newtonian gravity applies). GR shows that it can be either finite or infinite.
    I think it was around 2010. It's generally accepted that WMAP showed that the universe was flat. Before WMAP, people used to talk about the universe beginning as a point singularity, and being the size of a grapefruit at some point. See for example the timeline of the Big Bang written by Luke Mastin in 2009. He said "The linear dimensions of the early universe increases during this period of a tiny fraction of a second by a factor of at least 1026 to around 10 centimetres (about the size of a grapefruit)".

    Quote Originally Posted by Strange View Post
    Citation needed. The possibility that the universe could be infinite has been around as long as I can remember (which is quite a long time!)
    And there was me thinking Big Bang cosmology was mainstream. Now people are trying to tell me the universe was infinite when the Big Bang occurred, and is even more infinite now.

    Quote Originally Posted by Strange View Post
    I would say that Sean Carroll is a pretty reputable source. And I cannot see anything contentious on that page.
    I can. He thinks gravitational field energy is negative, he thinks energy is not conserved, he thinks spacetime expands rather than space, and he thinks the force causing the universe to accelerate is gravity.

    Quote Originally Posted by Strange View Post
    Perhaps you could point out the errors in this paper, rather than just saying you think it "tosh". If not, why should we take your opinions seriously?
    You should take my opinions seriously because I can back up what I say with evidence and references. I could point out the errors in that paper, but to do so would take me some time. More time than I really want to spend on the holographic universe. Meanwhile please note that there's plenty of evidence for general relativity, plenty of evidence for black holes, and plenty of evidence for the expanding universe. But there's no evidence for the holographic universe. None whatsoever.

    I fixed the link.
    Last edited by The Physics Detective; 2019-Jan-22 at 02:56 PM.

  12. #12
    Quote Originally Posted by Ken G View Post
    The problem is that "the mainstream view" is not always a single monolithic entity when you get to the frontier of any field.
    I agree with that Ken. When I was younger everything seemed cut and dried. Now I know more, it isn't. Hence this thread.

    Quote Originally Posted by Ken G View Post
    This is nothing unusual-- we often like to imagine we live in a world of black and white, but all we have to do is look to be introduced to the color gray. I'm sure this holds in any field-- if you ask a group of biologists what is "mainstream" about Darwinian evolution, you will find very good agreement about topics well away from the current frontier, and a whole lot of disagreement by the time you get to the frontier. Frontiers are always gray.
    Agreed. In cosmology the frontiers are grey, and I rather think some of the fundamentals aren't lily white either.

    Quote Originally Posted by Ken G View Post
    Then there is also the issue, mentioned above, of the difference between a theory and an interpretation of a theory. One can say that two theories are the same if they make all the same predictions, even if they are interpreted in very different ways. For example, there is the theory of Newtonian mechanics, where we have force F producing acceleration a=F/m, and then there is Lagrangian mechanics, where we have a scalar function (the "action") that nature somehow strives to minimize. These are the same theories, but they make completely different sounding claims about what is the cause an effect-- Newton says forces cause acceleration, Lagrange says forces are a kind of make believe ramification of the need to minimize action.
    I agree that there's an issue of theory and interpretation. But I think we do physics and cosmology to understand the world. I don't like it when I hear people dismissing understanding as mere interpretation or philosophy.

    Quote Originally Posted by Ken G View Post
    Then you have quantum mechanics, which also makes the same predictions as Newtonian mechanics on the macro scale, but has wave functions and complex amplitudes (and does differ on the micro scale, but it could still have been the way we describe macro phenomena in Newton's day had we the mathematics then).
    Quantum mechanics is an interesting subject. As is quantum field theory. Perhaps we could talk abut that some time.

    Quote Originally Posted by Ken G View Post
    So the bottom line is, we have to recognize that even experts disagree when you get to the frontiers of their fields (some experts think the disagreements between quantum theory and GR must be resolved by a theory of quantum gravity, others think it must be resolved by a new quantum theory).
    I'm just a IT guy with an interest in physics rather than some professor. But I side with the latter viewpoint.

    Quote Originally Posted by Ken G View Post
    So the concept of "mainstream" becomes gray there, not black and white. And two experts might create all the same predictions using completely different sounding models about what is causing those predictions to hold, so what is "mainstream" can involve multiple possibilities.
    Noted. For example...

    Quote Originally Posted by Ken G View Post
    This requires a special definition of energy that is not necessarily widely accepted. Many would say that GR does not support a global concept of energy in general, but in special situations it might be useful to define some special version of energy that has the property of being zero. Energy is not so much a thing as it is a calculational tool
    I disagree. I take note of Einstein's E=mc² paper. The mass of a body is a measure of its energy-content. Matter is made of energy. Energy isn't just a calculation tool.

    Quote Originally Posted by Ken G View Post
    a fact that is evident any time we invoke Newtonian gravity to use a change in gravitational potential energy mgh to calculate a change in kinetic energy when we drop something through distance h-- the result holds regardless of where we take the zero of the gravitational potential, so it holds regardless of what we think the energy there "really is."
    Only we know about the mass deficit. We know that when "two objects are attracting each other in space through their gravitational field, the attraction force accelerates the objects, increasing their velocity, which converts their potential energy (gravity) into kinetic energy". Then when they combine, this kinetic energy is dissipated, and the mass of the cold bound system is less than the original mass of the two bodies.

    Quote Originally Posted by Ken G View Post
    And in quantum mechanics, you can shift the complex phase of the total wavefunction of any closed system by any amount you like, and it will have no observable consequences, so we can say there is no "actual" wavefunction of a system, even though it might be mainstream to imagine that the wavefunction is a kind of "thing" that takes on actual values of its amplitudes, similar to energy.
    I think of the wavefunction as thing. I remember the Physics World top 10 breakthroughs for 2011 where second place went to "measuring the wavefunction" by Jeff Lundeen et al.

    Quote Originally Posted by Ken G View Post
    That depends on the meaning of the word "valid", which is not a well defined term in mainstream physics. I would be inclined to define "valid" as meaning "gives predictions that agree at some given desired level of accuracy", since I can't think of any other scientifically valid meaning of the term valid. Yet your source clearly takes the meaning "is exactly true," which is not a scientifically useful meaning of anything. So I don't think that source is correct, but it doesn't mean it's not mainstream-- as long as you take their rather problematic meaning of "valid." So these are the kinds of gray areas I'm talking about.
    Noted, but I don't think this one is a grey area. The principle of equivalence, the one where people say being in an accelerating spaceship is equivalent to standing on the surface of the Earth, is only valid in the infinitesimal. So it isn't valid in the room you're in. So like Synge said on page ix and x, ditch it because it causes confusion.

    Quote Originally Posted by Ken G View Post
    This issue is more like the question of interpretation. Consider any situation where you have a mundane Doppler shift of light in a vacuum. These situations don't really even require relativity if the speeds are not large, because you get a similar expression, to a good level of accuracy at low speeds, for the Doppler shift of sound without any relativity. But where you see the big difference is when you ask, "when did the Doppler shift occur?" For sound, if the source is moving through the air, the Doppler shift occurs when the sound is emitted, and if the receiver is moving through air, it occurs when the sound is heard (or any combination thereof). But for light, there is no "air" to resolve the issue, so you cannot say when the Doppler shift occurred. That's just what you get, you get an observed Doppler shift with no way to know when it happened, so you can interpret when it happened however you like.
    No you can't, because you and I can move towards the light at different speeds and compare notes. We know we measure those different frequencies because of our different speeds. We also know that Einstein described space as a thing that is "partly conditioned by the matter existing outside of the territory under consideration". There is space to resolve the issue.

    Quote Originally Posted by Ken G View Post
    In practice, the interpretation you use is determined by whatever coordinate system you choose to make the calculation. So the answer to "what happened" is basically "it depends on the coordinates you use to say what happened." That's a perfectly mainstream state of affairs, and it's just what is going on with the question of when gravitational redshifts happen, but it might make experts sound like they are disagreeing when in fact they are merely using different coordinate language.
    Sorry, I don't agree with that. What happens happens, and it's real. It doesn't depend on what coordinate system you use to make a calculation.

    Quote Originally Posted by Ken G View Post
    This exposes a key "gray area" of physics: language. Einstein worked hard to make the predictions of relativity coordinate independent, because he strongly believed that the laws of physics need not choose any particular coordinates. He succeeded famously, but the irony of that success is that language is already a kind of coordinate system. Hence, if the laws of physics must be coordinate independent, they can never be translated into everyday language...
    I'm afraid I reject that, Ken. It's giving up.

    Quote Originally Posted by Ken G View Post
    So your question is actually alluding to a very fundamental problem of physics-- we would like to be able to have more than just predictive equations, we want lessons and concepts and understanding.
    Agreed. We do physics to understand the world. Not to shut up and calculate.

    Quote Originally Posted by Ken G View Post
    But the latter will never be the same as the former, as the former can be expressed in an invariant form that depends on nothing that has anything to do with the person using them, and the latter quite obviously cannot be expressed that way. What is mainstream when it comes to the equations is normally quite black-and-white, but what they are telling us is generally rather gray.
    Noted. Let's all try to make it less so.
    Last edited by The Physics Detective; 2019-Jan-22 at 05:13 PM.

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    Quote Originally Posted by The Physics Detective View Post
    I agree that there's an issue of theory and interpretation. But I think we do physics and cosmology to understand the world. I don't like it when I hear people dismissing understanding as mere interpretation or philosophy.
    I agree, but we must accept the double-edged sword there. If we want to regard our physics as having lessons about how things really are, we have to accept not only philosophical elements, but also sociological ones. For example, if we ask whether the Earth really goes around the Sun, or the Sun really goes around the Earth, we find this question is informed by science, but not answered by it-- the answer requires using science to inform essentially sociological choices. So that will always be a gray area.
    Quantum mechanics is an interesting subject. As is quantum field theory. Perhaps we could talk abut that some time.
    It's a big forum, lots of questions getting asked!

    I'm just a IT guy with an interest in physics rather than some professor. But I side with the latter viewpoint.
    I don't know if being a professor helps to answer that one! It's really anybody's guess.
    I disagree. I take note of Einstein's E=mc² paper. The mass of a body is a measure of its energy-content. Matter is made of energy. Energy isn't just a calculation tool.
    That paper has its context.
    Only we know about the mass deficit. We know that when "two objects are attracting each other in space through their gravitational field, the attraction force accelerates the objects, increasing their velocity, which converts their potential energy (gravity) into kinetic energy". Then when they combine, this kinetic energy is dissipated, and the mass of the cold bound system is less than the original mass of the two bodies.
    But all that is local, and can be regarded from a single inertial reference frame that includes both objects. The issue is how energy works when you don't have that any more, like cosmology.
    I think of the wavefunction as thing. I remember the Physics World top 10 breakthroughs for 2011 where second place went to "measuring the wavefunction" by Jeff Lundeen et al.
    But it doesn't have a definite phase, only a relative phase. So it's a problem when one talks about the wave function of the whole universe-- it would be ambiguous by the complex factor eix. It's a bit like the problem of orientation, where we can say that one line is parallel or perpendicular to another, but we cannot say how the whole universe is oriented, or where it is located. So location and orientation are not "things" for the whole universe, only for parts of the universe in relation to each other. The idea that the whole universe could have an orientation is again a kind of sociological construct that doesn't come from any observation.
    Noted, but I don't think this one is a grey area. The principle of equivalence, the one where people say being in an accelerating spaceship is equivalent to standing on the surface of the Earth, is only valid in the infinitesimal.
    No, that's what I don't agree with, because that statement is only true if you take valid=exact. But nothing is ever exact in science, so that equation would mean all of science is not valid. But science is valid, so in science, valid doesn't mean exact, it means "correct to some level of approximation." Once you see that, you see that the equivalence principle is scales whose size is defined by your accuracy criterion-- but not infinitesmal because the accuracy criterion is also not infinitesmal.
    So it isn't valid in the room you're in. So like Synge said on page ix and x, ditch it because it causes confusion.
    If you want to understand how much a laser beam aimed horizontally will dip down, it is very powerful to use the equivalence principle, because it is very easy to figure out how far the beam will be "left behind" by a room that is accelerating upward, knowing only the acceleration of gravity and no other GR machinery.
    No you can't, because you and I can move towards the light at different speeds and compare notes. We know we measure those different frequencies because of our different speeds.
    I didn't say the difference in speeds don't create the Doppler shifts, I said we could never say when the Doppler shifts occurred. This is true, we can use one coordinate system that says the shift happened right away upon emission, another that says it happened right before absorption, and another that says it accumulates slowly the whole way. So you see we could ask "when does mainstream physics say the Doppler shift happens," and look at people arguing over the answer, but the answer is that mainstream physics knows it has no answer to that question. Which is odd-- if a Doppler shift happens, how can it not be knowable when it happens? It turns out the concept of a "happening" is a more subtle than we realized.
    We also know that Einstein described space as a thing that is "partly conditioned by the matter existing outside of the territory under consideration". There is space to resolve the issue.
    That's essentially Mach's principle, and there are lots of debates about it but the general consensus seems to be that GR doesn't actually satisfy that version of Mach's principle. So GR is often not regarded as quite the theory Einstein set out to create. (Incidentally, Einstein called the equivalence principle his "happiest thought", which is saying a lot, so any source that asks us to reject that principle is certainly running afoul of Einstein's intentions.)
    What happens happens, and it's real. It doesn't depend on what coordinate system you use to make a calculation.
    Yet, when you said that, you used language, did you not? So is what you are saying independent of the language you chose? Does it mean something beyond what language can convey? If you say "yes", then you have to decide if you are talking about something other than what you are saying. Does one talk about what one is saying, or about what one is not saying?

  14. #14
    Quote Originally Posted by Ken G View Post
    I agree, but we must accept the double-edged sword there. If we want to regard our physics as having lessons about how things really are, we have to accept not only philosophical elements, but also sociological ones. For example, if we ask whether the Earth really goes around the Sun, or the Sun really goes around the Earth, we find this question is informed by science, but not answered by it
    I’m sorry Ken, but I must insist: the Earth goes round the Sun.

    Quote Originally Posted by Ken G View Post
    That paper has its context.
    I hope you’re not trying to tell me that E=mc² is wrong.

    Quote Originally Posted by Ken G View Post
    But all that is local, and can be regarded from a single inertial reference frame that includes both objects. The issue is how energy works when you don't have that any more, like cosmology.
    It’s clear how it works. Gravity converts potential energy into kinetic energy. That potential energy is mass-energy, in the body. Once the kinetic energy has dissipated the mass of the body is reduced. That’s why we call it a mass deficit.

    Quote Originally Posted by Ken G View Post
    But it doesn't have a definite phase, only a relative phase. So it's a problem when one talks about the wave function of the whole universe
    When wavefunction is real, it doesn’t make much sense to talk about the wavefunction of the whole universe.

    Quote Originally Posted by Ken G View Post
    No, that's what I don't agree with, because that statement is only true if you take valid=exact.
    I disagree, because “only valid in the infinitesimal” means “not valid in the room you’re in”. If you think it is, you end up misunderstanding why the horizontal light beam curves downwards.

    Quote Originally Posted by Ken G View Post
    If you want to understand how much a laser beam aimed horizontally will dip down, it is very powerful to use the equivalence principle, because it is very easy to figure out how far the beam will be "left behind" by a room that is accelerating upward, knowing only the acceleration of gravity and no other GR machinery.
    And if you want to understand why the horizontal light beam curves downwards? Ken, please explain that in your next post. This is important, please give it your best shot.

    Quote Originally Posted by Ken G View Post
    but the answer is that mainstream physics knows it has no answer to that question
    Again I beg to differ. Mainstream physics knows full when that when you move towards a light source, that’s when you see the Doppler shift happening.

    Quote Originally Posted by Ken G View Post
    That's essentially Mach's principle, and there are lots of debates about it but the general consensus seems to be that GR doesn't actually satisfy that version of Mach's principle.
    That isn’t Mach’s principle. Mach’s principle claims inertia is to do with “distant stars”, and it isn’t. It’s to do with energy-content and the wave nature of matter.

    Quote Originally Posted by Ken G View Post
    So GR is often not regarded as quite the theory Einstein set out to create. (Incidentally, Einstein called the equivalence principle his "happiest thought", which is saying a lot, so any source that asks us to reject that principle is certainly running afoul of Einstein's intentions.)
    You killed two birds with one stone there. Einstein’s “happiest throught” equivalence principle is not the equivalence principle that people now claim to be central to GR.

    Quote Originally Posted by Ken G View Post
    Yet, when you said that, you used language, did you not? So is what you are saying independent of the language you chose? Does it mean something beyond what language can convey? If you say "yes", then you have to decide if you are talking about something other than what you are saying. Does one talk about what one is saying, or about what one is not saying?
    I’m talking about physics and cosmology, and about what’s mainstream. And I'm picking up some interesting information here.

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    Quote Originally Posted by The Physics Detective View Post
    I’m sorry Ken, but I must insist: the Earth goes round the Sun.
    If I am not mistaken, a model with a stationary, non-rotating Earth is admissible in General Relativity. I would expect it to be dreadfully messy and not very useful for practical analysis, but that does not necessarily mean that it is invalid in principle. As always, don't take my word as gospel. I would cheerfully search for corroborating references if I knew what words to put in a search engine. A good reference librarian in a college or university physics library would be most welcome.

    I hope you’re not trying to tell me that E=mc² is wrong.

    It’s clear how it works. Gravity converts potential energy into kinetic energy. That potential energy is mass-energy, in the body. Once the kinetic energy has dissipated the mass of the body is reduced. That’s why we call it a mass deficit.

    When wavefunction is real, it doesn’t make much sense to talk about the wavefunction of the whole universe.

    I disagree, because “only valid in the infinitesimal” means “not valid in the room you’re in”. If you think it is, you end up misunderstanding why the horizontal light beam curves downwards.

    And if you want to understand why the horizontal light beam curves downwards? Ken, please explain that in your next post. This is important, please give it your best shot.

    Again I beg to differ. Mainstream physics knows full when that when you move towards a light source, that’s when you see the Doppler shift happening.

    That isn’t Mach’s principle. Mach’s principle claims inertia is to do with “distant stars”, and it isn’t. It’s to do with energy-content and the wave nature of matter.

    You killed two birds with one stone there. Einstein’s “happiest throught” equivalence principle is not the equivalence principle that people now claim to be central to GR.

    I’m talking about physics and cosmology, and about what’s mainstream. And I'm picking up some interesting information here.

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    Greetings. Your points seem toward the view that reality does not need interpretation. This reality issue was debated at length in another thread. However if i can use one small example from above, I can say the sun rotates around me and it’s an observable fact. I accept the interpretation that the earth is a planet in orbit around the sun but if i choose my frame of reference the cosmos is rotating around me. The mainstream view is an interpretation of our agreed observations.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  17. #17
    And yet it moves.

    Hornblower, Profloater: mainstream physics does not support the notion that the Sun moves around the Earth. Let's assume that you were a pair of venerable astronomers, at the top of your field. If you were to come up with some "model" using an Earth-centered coordinate system, I'm sure nobody would object. However if you then tried to claim that this model bears any resemblance to reality, you would be laughed out of court. If you then huffed and puffed and declared that this is mainstream, I rather think the laughter would stop, along with your funding.
    Last edited by The Physics Detective; 2019-Jan-23 at 05:30 PM.

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    Quote Originally Posted by The Physics Detective View Post
    Hornblower, Profloater: mainstream physics does not support the notion that the Sun moves around the Earth. Let's assume that you were a pair of venerable astronomers, at the top of your field. If you were to come up with some "model" using an Earth-centered coordinate system, I'm sure nobody would object. However if you then tried to claim that this model bears any resemblance to reality, you would be laughed out of court. If you then huffed and puffed and declared that this is mainstream, I rather think the laughter would stop, along with your funding.
    I doubt a modified Tychonic model has ever been falsified, though it would be bizarre and include fictitious forces. Science is objective-based and laughter is irrelevant to it directly, but we tend to favor mainstream views, which is a subjective viewpoint and usually a wise one, but not always.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by The Physics Detective View Post
    And yet it moves.

    Hornblower, Profloater: mainstream physics does not support the notion that the Sun moves around the Earth. Let's assume that you were a pair of venerable astronomers, at the top of your field. If you were to come up with some "model" using an Earth-centered coordinate system, I'm sure nobody would object. However if you then tried to claim that this model bears any resemblance to reality, you would be laughed out of court. If you then huffed and puffed and declared that this is mainstream, I rather think the laughter would stop, along with your funding.
    If you have an Earth-centered coordinate system (eg the one used by GPS) then the Sun would go round the Earth in that system and it would represent reality.

  20. #20
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    Quote Originally Posted by The Physics Detective View Post
    And yet it moves.

    Hornblower, Profloater: mainstream physics does not support the notion that the Sun moves around the Earth. Let's assume that you were a pair of venerable astronomers, at the top of your field. If you were to come up with some "model" using an Earth-centered coordinate system, I'm sure nobody would object. However if you then tried to claim that this model bears any resemblance to reality, you would be laughed out of court. If you then huffed and puffed and declared that this is mainstream, I rather think the laughter would stop, along with your funding.
    I find it strange that you insist the earth moves round the sun, of course it does, but that’s choosing a sun centred frame. Any two bodies in relative movement can be viewed from either as base. For many earthbound tasks the sunrise and sunset can be modelled as the sun rotating around us and the mental exercise of understanding that is the core underpinning of the next models within relativity. In that case obviously the solar system model is the most useful. If you took a more distant viewpoint you could see the sun progressing around our galaxy, relative to other galaxies and the Earth following an epicyclic path. Relativity teaches us to think of our frame of reference. So I still do not understand your point about the mainstream of all those more complex issues. I am sure I do not have to rehearse the fact that quantum mechanics and general relativity do not agree about gravity etc. So we do know there is more to interpret.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by The Physics Detective View Post
    I’m sorry Ken, but I must insist: the Earth goes round the Sun.
    Insisting is unscientific. Many would have insisted the opposite for a thousand years, it means nothing to insist now because science is never frozen in place. Nor can you claim that modern knowledge convinces us the Earth goes around the Sun-- modern knowledge tells us that motion is relative, and that what goes around what is always a question of perspective. Hence, the claim that Earth goes around the Sun is sociological, not scientific. It's fine to say, sociologically speaking, but it is saying more about us and our ways of thinking than it is about the laws of physics or the solar system.
    I hope you’re not trying to tell me that E=mc² is wrong.
    Of course it's wrong, everything in science is wrong at some level. The only question is, to what level shall we go? The equation has its domain of applicability, as do all equations. But it is well known that there is not a global concept of energy in general in GR, but there can be one under special conditions that are relevant to a lot of situations of interest.
    It’s clear how it works. Gravity converts potential energy into kinetic energy. That potential energy is mass-energy, in the body.
    Again, you are taking a particular perspective, a simplified one where there is not a background spacetime against which this is all happening. Yours is a useful simplification, but not a statement of fact.
    When wavefunction is real, it doesn’t make much sense to talk about the wavefunction of the whole universe.
    I don't know where you get that idea from, most people who think the wavefunction is real think the universe has one. For the simple reason that if it's real, then it's what's really happening, so the universe would need one to know what to do. It is probably naive to think the wavefunction is what is really happening, but this gets into what you mean by your word "real," and how you use language-- so is more sociology.
    I disagree, because “only valid in the infinitesimal” means “not valid in the room you’re in”. If you think it is, you end up misunderstanding why the horizontal light beam curves downwards.
    Not at all, my whole point is that you can understand completely why the beam curves using the equivalence principle without any tidal effects. So it's quite valid in the room, that's where it works great.
    And if you want to understand why the horizontal light beam curves downwards? Ken, please explain that in your next post. This is important, please give it your best shot.
    It's quite simple-- just analyze it from a frame where the room is accelerating upward. Start with the room at zero speed (it's arbitrary), and let it speed up upward as the light goes across. In the frame of the analysis, the light goes straight across because that's how it was emitted, but the room goes upward. You can calculate precisely where it will hit the wall on the other side by simply calculating how far the room rises as the beam is going across. It's just that easy! Works for any horizontal beam of anything, because it really doesn't have anything to do with light. But that's why it gives such a great answer to the question of why everything falls the same, even light.
    Again I beg to differ. Mainstream physics knows full when that when you move towards a light source, that’s when you see the Doppler shift happening.
    You are not understanding how I am using the "when" question. I am asking, what is the moment that the light was Doppler shifted? So "when" means the specific question "at what time," not the general "under what circumstances." So again I ask-- did the light get shifted when it was emitted, when it was absorbed, or all along the way? You see the relevance to the same question about gravitational redshifts-- did it happen as the light climbed upward, or did nothing happen to the light, it was something about the receiver that did it? The "aha" moment is when you realize that questions like this are formed in human language, not in the language of a physics equation, and as such, the answer will depend on the perspective. Perspective affects language, this is the crucial realization. But Einstein's great accomplishment was to find laws of physics that do not depend on perspective, so we have the hidden cost of his success: attempts to take lessons from those laws will lose this key aspect. Lessons are always dependent on perspective, and hence they are never unique-- hence the appearance of disagreement, even in the "mainstream."
    Last edited by Ken G; 2019-Jan-24 at 06:39 AM.

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    Quote Originally Posted by George View Post
    I doubt a modified Tychonic model has ever been falsified, though it would be bizarre and include fictitious forces.
    The necessary forces appear automatically from Einstein's equations. They may have a difficult interpretation, but there they are, in the equations-- when the corresponding reference frame is expressed in the choice of coordinates. We can call them fictitious, but remember, even the force of gravity is fictitious in Einstein's approach! Or more correctly, we might say that laws of physics that do not distinguish inertial and noninertial frames (including GR) banish the distinction between gravity and fictitious forces, so one could say they make fictitious forces less bizarre by making them more like good old gravity.
    Last edited by Ken G; 2019-Jan-24 at 06:52 AM.

  23. #23
    George/Strange/Profloater/Ken: I am tempted to start an Against the Mainstream thread entitled The Sun does not go round the Earth. I can play the part of Galilieo. You can play the part of the Inquisition. How does that sound to you?

    Quote Originally Posted by Ken G View Post
    Insisting is unscientific. Many would have insisted the opposite for a thousand years, it means nothing to insist now because science is never frozen in place. Nor can you claim that modern knowledge convinces us the Earth goes around the Sun... Of course it's wrong... Yours is a useful simplification, but not a statement of fact.
    The Earth goes round the Sun, E=mc² is not wrong, and gravity does convert potential energy into kinetic energy - the mass deficit is not some fiction. I don't want to talk about "the wave function of the universe". And I'm not going to repeat myself about that Doppler shift. Let's talk about something else instead. Let's talk about gravity.

    Quote Originally Posted by Ken G View Post
    Not at all, my whole point is that you can understand completely why the beam curves using the equivalence principle without any tidal effects. So it's quite valid in the room, that's where it works great... It's quite simple-- just analyze it from a frame where the room is accelerating upward. Start with the room at zero speed (it's arbitrary), and let it speed up upward as the light goes across. In the frame of the analysis, the light goes straight across because that's how it was emitted, but the room goes upward. You can calculate precisely where it will hit the wall on the other side by simply calculating how far the room rises as the beam is going across. It's just that easy! Works for any horizontal beam of anything, because it really doesn't have anything to do with light. But that's why it gives such a great answer to the question of why everything falls the same, even light.
    That isn't why the beam curves downwards. The room is not accelerating upwards. And see Professor Ned Wright's deflection and delay article. The deflection of light is twice the deflection of matter. I'm afraid your answer is wrong. Would you like to have another try?

    Einstein-wavelets-75.gif

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    Quote Originally Posted by The Physics Detective View Post
    I’m sorry Ken, but I must insist: the Earth goes round the Sun.
    Be careful of absolute statements about physics, especially when you a self-described non-expert are disagreeing with physics interpretations. Besides relativity concerns, the center of earth's orbit is a long ways from the sun, and even one of its focuses is not the center of the sun (I understand that that distinction is not what is being discussed, but still...)
    I hope you’re not trying to tell me that E=mc² is wrong.
    Even the paper you linked (that's not really the "E=mc2 paper," is it?) points out that they ignore terms of fourth magnitude and higher.

    And I'm picking up some interesting information here.
    These conversations can be helpful! As you seem to be finding out, what seems to be inconsistencies to a non-expert turn out to be completely valid when you understand things better.

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    Am I wrong or was grapes post the last post since yesterday morning? I couldn't get into any thread.
    We know time flies, we just can't see its wings.

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    Same here , I think the board crashed.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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    Quote Originally Posted by Ken G View Post
    The necessary forces appear automatically from Einstein's equations. They may have a difficult interpretation, but there they are, in the equations-- when the corresponding reference frame is expressed in the choice of coordinates.
    I assume that the GR model properly addresses acceleration regardless of the chosen frame, so the forces necessary to those accelerations are a given. Is that an accurate way to address these forces?

    We can call them fictitious, but remember, even the force of gravity is fictitious in Einstein's approach!
    Okay, that's helpful since I believe "fictitious" is the mainstream word for them and one you use, but your point is that it's not synonymous with fantasy.

    Or more correctly, we might say that laws of physics that do not distinguish inertial and noninertial frames (including GR) banish the distinction between gravity and fictitious forces, so one could say they make fictitious forces less bizarre by making them more like good old gravity.
    Yes, and that's where it gets interesting for me, at least. A tweaked Tychonic model, though clunky and illogical seems to get more sour with vast distances. I think you mentioned Mach had some things to say about it and Newton had his spinning bucket of water example, I think. But that aside, it's the simple strangeness that the power of GR doesn't bring any kind of mathematical advantage to a more heliocentric model. So it has the potential of falling into the category of the greatest thing that can be said for scientific discoveries-- "that's funny", and not "Eureka! [Who said that? Clarke?]

    Also, since Galileo is with us, how interesting it is that he avoided the Tychonic model. It's assumed he saw it as preposterous, yet he saw the Church (via the Jesuits) adopt it. Or, did he know that he couldn't falsify it and, instead, tried to proof the Copernican model with his brilliant, but erroneous, tide claims? Perhaps it was both. There are some nuances to all this as it affected his relationships with other scientists and clergy, good and bad.
    Last edited by George; 2019-Jan-25 at 08:25 PM.
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    Quote Originally Posted by Roger E. Moore View Post
    Same here , I think the board crashed.
    Yep, Hope the others come back.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by The Physics Detective View Post
    George/Strange/Profloater/Ken: I am tempted to start an Against the Mainstream thread entitled The Sun does not go round the Earth. I can play the part of Galilieo. You can play the part of the Inquisition. How does that sound to you?
    The Italian Inquisition, much softer than the Spanish one, did not address scientific investigation but judicial behavior, addressing things like heresy, which Galileo was not found to have committed, but very close in their opinion.

    The fact that GR can produce a model using a fixed Earth reference frame whereby the Sun is seen to go around the Earth, then it is a nice fit with the fact that we see it do so every day. It is odd that it doesn't somehow favor a more heliocentric model instead, so that's interesting but perhaps not.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    The Italian Inquisition, much softer than the Spanish one, did not address scientific investigation but judicial behavior, addressing things like heresy, which Galileo was not found to have committed, but very close in their opinion.

    The fact that GR can produce a model using a fixed Earth reference frame whereby the Sun is seen to go around the Earth, then it is a nice fit with the fact that we see it do so every day. It is odd that it doesn't somehow favor a more heliocentric model instead, so that's interesting but perhaps not.
    In a purely practical sense GR does favor a more heliocentric model, as it then converges numerically with Newton's theory when used to calculate the dynamics that explain our observations. As I think I understand it, that does not necessarily mean it is "correct" and other models are "incorrect" in some absolute sense.

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