Is there any experimental or observational confirmation of curvature of spacetime?

Discussion in 'Physics & Math' started by Ultron, May 31, 2016.

  1. Dr_Toad It's green! Valued Senior Member

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    Wow. You missed a lot, eh?
     
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  3. geordief Valued Senior Member

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    From my lowly state of appreciation of the subject ,that was /is something that also annoyed me when I realised it ..

    Can I "resolve" my annoyance ,though by replacing the lack of movement in the model with an "expansion" of the model as seen from the origin (or really from any frame of reference)?

    It is not the same thing as the notion of motion or speed but it is a change in time and space in that the larger the model is , (the more the spatial or temporal axes are prolonged) the further away we are from the particular origin.

    We could even imagine ourselves "surfing" the "wave front" of the expanding model (the model -not any reality)

    I just say this as a kind of "reassurance" not as a way to explain (or indicate that I have understood) anything important.
     
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  5. Write4U Valued Senior Member

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    I was thinking more along the lines of kinetics. Speed = Force . Is that not why we use the term "rest-mass"? IOW, regardless of mass, an object in motion exerts a force, even as the object itself has *zero rest-mass*.
     
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  7. Layman Totally Internally Reflected Valued Senior Member

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    The reason people "should" use the term rest-mass is to distinguish it from a situation where it would have a relativistic mass due to its velocity, since Einstein predicted that an object would have a greater amount of mass from traveling at a relative velocity. The only reason why someone "should" think that an object has momentum or be able to exert a force even though it has zero mass is because Einstein predicted that energy density could exert a gravitational pull. Then I believe that little about how or why Einstein came to those predictions is even known. It is just mentioned in his paper about Einstein-Rosen bridges about how "electricity" can influence the gravitational field. Then civilization will not have the technology to test such predictions for possibly thousands of years, because it would require all of the energy of the sun all concentrated into one machine at one single point in time. That is why people like Michio Kaku try to make predictions about when civilization will reach a stage to make those types of things possible. It is entirely possible that particles that travel the speed of light have zero rest mass and zero relativistic mass as well. If anyone else not named Einstein with big crazy grey hair wrote about how "electricity" shapes gravitational fields, they would just be laughed at and ridiculed...
     
  8. rpenner Fully Wired Valued Senior Member

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    Please don't misteach physics on the main science forums.
     
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  9. BdS Registered Senior Member

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  10. Layman Totally Internally Reflected Valued Senior Member

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    Couldn't help but wonder how it is even possible that you would say this about what I said... There was no need to state that something had rest mass before Einstein, because as far as anyone knew before then, mass was the just mass. Mass was the same at rest or not, because they didn't have general relativity. That fact that you would post this is just absolutely ridiculous, and you have no place deciding what is or not science here. I guess that explains why you can only spout out equations all the time and never really give any input on anything.
     
  11. rpenner Fully Wired Valued Senior Member

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    Citation requested. Because Wikipedia says something different.
    https://en.wikipedia.org/wiki/Mass_in_special_relativity#The_relativistic_mass_concept

    You have your history wrong. Einstein invented photons where \(E = c \left| \vec{p} \right| \) in 1905, the same year he introduced special relativity which would define \(E^2 = \left( mc^2 \right)^2 + \left( c \vec{p} \right)^2\). The concepts of energy and momentum conservation, turned out to be more fundamental than Newton's assumption that \(\vec{p} = m \vec{v}\). Instead the correct relation between momentum, mass and velocity is \(\vec{p} = \sqrt{ m^2 + \frac{1}{c^2} \vec{p}^2 } \vec{v}\), which has solutions where \(m > 0, |v| < c\) and solutions where \(m = 0, |v| = c\). The last family of solutions has no constraints on what momentum is because, as Einstein points out in 1909, the momentum of a photon is \(|\vec{p}| = h/\lambda\) which has been very useful in a number of contexts.
    https://en.wikipedia.org/wiki/Photoelectric_effect
    https://en.wikipedia.org/wiki/Photon#Historical_development

    So it looks like you are making an argument from willful ignorance rather than looking for evidence.

    Your embrace of your status of a physics outsider leaves you no ground to substitute your opinion as a well-supported claim.

    Yes, his 1935 paper, considered electrovacuum solutions like the 1916-1918 Reissner–Nordström geometry. It differs from a Schwarzschild geometry by also solving the Maxwell equations in curved space-time and taking that into account in the solution to Einstein's field equations. Mocking it just shows that you are a hundred years behind.

    That does not follow if you are talking about electrovacuum solutions to general relativity in that electromagnetic effects around black holes can be significant without human engineering.
    And in 1962, another paper largely closed the door on engineering such wormholes.

    You have not supported this point, either. Why can't Prof. Kaku be a run-of-the-mill self-promoting science/futurist cheerleader?

    They do, only in the limit of \(\lambda \to \infty\).

    Einstein, Reissner, Nordström, Kerr, Newman, etc, etc.
    Before Einstein, people didn't need to distinguish between rest mass and relativistic mass as the dichotomy of these concepts had not been invented; therefore, as rest mass is the direct successor to inertial mass in post-Newtonian dynamics while relativistic mass can only fill in for inertial mass when acceleration and velocity are at right angles and using deprecated Newtonian formula, use relativistic mass is misleading. Einstein's relativity does not predict that mass increases with velocity, it predicts that every massive particle has the same dynamics in a coordinate system where it can be considered (instantaneously) at rest. Thus the defining mass property of an electron is the electron rest mass. Einstein's earliest papers had lots of bridges to the way physics was done before Einstein, but by 1916 at least, he was using m without any subscript to mean rest mass.

    Special relativity, I think you mean.
    It's the function I was asked to perform, by forum staff.
    Do you troll Baudelaire poetry boards asking why they fill all their posts with French? You are very bad at attributing motives to others, which causes others to attribute to you a sullen laziness that would explain your willful ignorance and blinkered false equivalence of opinions issuing from the minds of the informed and uninformed.
     
  12. black mask Registered Member

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    Then what would u call rotation of earth or around sun or do u think that gravity act like like a power glass to bend light?
     
  13. Layman Totally Internally Reflected Valued Senior Member

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    I see no reason to discuss anything with you beyond this point, because this is reaching a whole new level of ignorance. I guess this proves that it is not always true that someone that knows the maths knows the concepts (that is also assuming any of your math you always spill on this forum is even correct). I guess that is why you rarely post anything in actual English on these forums.
     
  14. Layman Totally Internally Reflected Valued Senior Member

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    The only thing I agree with from Taylor and Wheeler is that interpretations of GR may have been in error when saying that an object could measure or detect its own mass increase due to an increase in its relative velocity. Yes, I do mean GR, not SR! The reason for that is because it implies that there is a preferred frame of reference. An object would never be able to know its true velocity, but it would be able to in that interpretation by measuring its own mass. The sad thing is that they have recently added to this concept to say that an object would have no relative mass increase, apparently. But, they are not the say all, end all on the subject. These are radical opinions, and anything they say about SR and GR should be taken with a grain of salt.
     
  15. Layman Totally Internally Reflected Valued Senior Member

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    On the flip side, of all this nonsense, Hawking and Susskind took a completely different direction with relativity. They go as far to say that an object would slow down due to time dilation, instead of trying to do away with time dilation altogether. Then an object cannot measure its own time dilation or change it would have on its velocity. If Taylor or Wheeler where working on that problem, they probably would have said that it proves there is no time dilation, because it would not provide a self consistent theory. What they have been trying to do is basically that, with relative mass increases. So, it appears that the scientific community is really divided on this problem right now. I think that it just means that an observer could not detect his own time dilation (just like in classical SR).

    We have Taylor and Wheeler saying that relativistic mass increase is false, because it would change the objects relative velocity. Then we have Hawking and Susskind saying that Hawking radiation is false (from the Holographic Universe theory), because of an observer freezing on the event horizon of a black hole (instead of saying GR is wrong). All of this could simply be avoided by just saying that an observer cannot measure his/her own relativistic effects in GR...

    A watch would no longer keep ticking falling into a black hole, but it would keep falling. It is just that quantum theory does not distinguish between those two events (of a macroscopic object), so the interpretations are just wrong.
     
  16. rpenner Fully Wired Valued Senior Member

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    As I suspected, you cannot provide a citation to where Einstein embraced relativistic mass because he embraced initially (1905) two forms of relativistic mass in SR dynamics, the longitudinal mass, \(M_{\parallel} \equiv \gamma^3 m\), and the transverse mass, \(M_{\perp} \equiv \gamma m\). But for an arbitrary force not in one of these special direction, force would not even be parallel to acceleration so what was needed was new dynamics not a new definition of mass.

    You have not meaningfully replied to my analogy about your mathematical illiteracy and willful ignorance, “Do you troll Baudelaire poetry boards asking why they fill all their posts with French?”, but rather have doubled down on your meritless position.
    Citation required. Are you referring to Spacetime Physics, first edition; Spacetime Physics, second edition; or some other source?
    In Spacetime Physics, second edition, (1992) pp 250-251, we have this Q and A exchange:
    Is the mass of a moving object greater than the mass of the same object at rest?
    No. It is the same whether the object is at rest or in motion; the same in all frames.​

    Really? Isn’t the mass, \(M\), of a system of freely moving particle given, not my the sum of the masses \(m_i\) of the individual constituents, but by the sum of the energies \(E_i\) (but only in a frame in which total momentum of the system equals zero)? Then why not give \(E_i\) a new name and call it “relativistic mass” of the individual particle? Why not adopt the notation
    \(m_{i,rel} = E_i = m_i + K_i\) ?
    With this notation, can’t one then write
    \(M = \sum_{i=1}^{n} m_{i,rel}\) ? (in zero-total momentum frame)
    Ouch! the concept of “relativistic mass” is subject to misunderstanding. That’s why we don’t use it. First, in applies the name mass — belonging to the magnitude of a 4-vector — to a very different concept, the time component of a 4-vecotr. Second it makes increase of energy of an object be velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of space-time itself.​

    In order to make this point clear, should we call invariant mass of a particle its “rest mass”?
    That is what we called it in the first edition of this book. But a thoughtful student pointed out that the phrase “rest mass” is also subject to misunderstanding: What happens to the “rest mass” of a particle when the particle moves? In reality mass is mass is mass. Mass has the same value in all frames, is invariant, no matter how the particle moves. [Galileo: “In questions of science the authority of a thousand is not worth the humble reasoning of a single individual.”] ​

    Taylor and Wheeler repeat and reference the above-quoted dialog in a box in chapter one of their introductory textbook on GR called Exploring Black Holes, in a box at the end of chapter 1, section 7:

    The fact that no object moves faster than the speed of light is sometimes “explained” by saying that “the mass of a particle increases with speed.” This interpretation can be applied consistently, but what could it mean in practice? Someone riding along with a faster-moving stone detects no change in the number of atoms in the stone, nor any change whatever in the individual atoms, nor in the binding energy between atoms. Our viewpoint in this book is that mass is an invariant, the same for all free-float observers when they use equations [32] or [33] to reckon the mass. In relativity, invariants are diamonds. Do not throw away diamonds! ​
    http://www.eftaylor.com/pub/chapter1.pdf
    But this chapter not about GR but SR. That's why you are requested to make some specific reference.
    Your thinking is muddled here. If relativistic mass was important to physics, why couldn't one measure one's own relativistic mass? Because velocity is not a thing, only relative velocity, according to the theory of special relativity (and also general relativity). Therefore relativistic mass is not a thing, only relativistic mass relative to some imaginary choice of a standard of rest. Thus rest mass is free to be a real thing, to the extent that Taylor and Wheeler simply call it mass.

    You didn't run through the exercises in these textbooks did you? They do cover mass increase of systems of particles.
    These are introductory textbooks.
    Citation requested.
     
  17. rpenner Fully Wired Valued Senior Member

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    While they have authored some pop science books and plenty of scientific articles, I cannot identify any paper or book they co-authored. So ... citation requested.

    This is likely to be your own muddled takeaway rather than their opinion. Time dilation is relative to some choice of a reference clock, while velocity is relative to some choice of a standard of rest. Assuming the reference clock is also the standard of rest, then there is a relation between time dilation and velocity but not a cause-and-effect relationship. They simply go hand-in-hand due to the geometry of space-time.

    Naturally, if the clock and standard of rest is also the system we are studying, it cannot have time dilation relative to itself, nor may it have a velocity relative to itself, so what thinking could a person use to assume that any object could measure its own time dilation??? These ideas are not new to Hawking and/or Susskind, but just new to you.

    Making patently false statements about Taylor and Wheeler does not flatter your ability to reason from facts.

    No one will ever know what you mean by “it”, because you did not provide a citation.

    Patently false.
    I assume you are referring to Susskind's 2008 pop science book The Black Hole War which was not co-authored by Hawking and did not claim there was no Hawking radiation, but a much more nuanced disagreement about quantum information and black holes. The observer never freezes on the event horizon but a remote observer is free to use a coordinate system where an inflating object freezes on the event horizon but that's just a poor choice of coordinate system for describing the object.

    Who is disagreeing with this? You have invented a fake disagreement.

    You are still muddled in that you have contradicted yourself.
    Gibberish. Quantum theory does indeed distinguish between clocks that tick and clocks that don't tick.
     

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