Widespread misconceptions about cosmic expansion

Discussion in 'Physics & Math' started by zanket, Dec 23, 2006.

  1. zanket Human Valued Senior Member

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    Widespread misconceptions about cosmic expansion

    First I will cover the current state of affairs, and then I’ll clear up some misconceptions that are held even by cosmologists.

    Cosmic expansion is defined as all of the distant galaxies receding from one another. In the leading cosmological model, space itself expands, and this is the cause of cosmic expansion. In the expanding space paradigm (hereafter just “the paradigm”), the big bang was an explosion of space in matter & energy, rather than an explosion of matter & energy in space, and the explosion continues to this day, with new space being created every moment. A common question is, if space is expanding, do our bodies expand since they contain space? The common answer is, no, because we’re gravitationally bound, which hardly answers the question. The full answer is that gravity and other binding forces easily overpower the expanding space on such a small scale. The paradigm does apply to our bodies, even on an atomic scale, and under certain hypothetical scenarios could rip our bodies apart, including even the atoms. At this point it’s good to emphasize that we’re talking about a paradigm that has not been definitively experimentally confirmed. It is just a model for explaining what we observe.

    One may wonder why cosmic expansion cannot be due simply to movement of the galaxies relative to one another. Why is the paradigm needed to explain cosmic expansion? Well, first of all, the paradigm allows for the concept of the galaxies moving relative to one another, so to avoid confusion we should be clear that we’re talking about so-called peculiar movement, which is movement relative to fixed points within the expanding space (imagine movement relative to intersections on an expanding grid), or movement in the absence of the paradigm. So we ask, why can’t cosmic expansion be caused by peculiar movement alone? Some answers may jump to mind: because then special relativity (SR) would be violated when two objects sufficiently far apart from each other recede from each other faster than c, the speed of light. Or you might think that the increasing volume of space between objects is explainable only by space itself expanding. Or you might think that peculiar movement alone results in a universe that has a center and an edge. Cosmologists feel that the paradigm is necessary, for whatever reason.

    Now I will dispel the notion that cosmic expansion cannot be caused by peculiar movement alone; that is, I will show that cosmic expansion can be caused by peculiar movement alone, with no ill effects. This will show that the paradigm is superfluous.

    Let an infinitely large universe have no method by which space itself expands or contracts—the paradigm doesn’t apply to this universe. Any two galaxies in this universe can recede from each other independently of the other galaxies. Then nothing prevents every two galaxies from receding from each other, which is the same as all of the galaxies receding from one another. SR (a single application of which can apply to an indefinitely large region in such a paradigm-less universe) ensures that every two galaxies recede from each other slower than c, even if every galaxy recedes from its adjacent neighbors at a relativistic velocity. No cosmic center or cosmic edge forms when any two galaxies recede from each other. Then neither do these form when every two galaxies recede from each another. Rather, from any vantage point galaxies recede at c in the limit at a limit of infinite distance.

    Now there is no longer a need for the paradigm. Our cosmological model can be streamlined. There is no longer a need for the "peculiar" qualifier for movement.

    To emphasize a key difference between cosmic expansion caused by expanding space (as described by the paradigm) versus caused by peculiar movement alone: With the paradigm, a sufficiently long straight thread floating in deep space is stretched and eventually breaks. Without the paradigm, the thread does not stretch regardless of its length.
     
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  3. 2inquisitive The Devil is in the details Registered Senior Member

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    zanket,
    What is the current radius of the observable universe from our vantage point? (about 48 billion lightyears) How old is the universe? (about 13.7 billion years) You do realize the distance to the 'standard candles', the type 1a supernovas, is determined by their relative luminousity, or brightness, and that distance is even farther away than their redshifts indicate? SR and the velocity addition rule is not applicable in a global frame of reference encompassing the entire universe.
     
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  5. Prince_James Plutarch (Mickey's Dog) Registered Senior Member

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    Although I have no problem with your post factually, artistically I'd say: Please, please, please pick up a theasarus and use an alternative for "paradign"? How about "model"?
     
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  7. zanket Human Valued Senior Member

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    3,777
    All of this may apply in a universe in which space itself expands. The story is different when space does not expand, and I show above that space need not expand in our cosmological model. The reason "SR and the velocity addition rule is not applicable in a global frame of reference encompassing the entire universe" is because space is thought to expand, and SR does not handle that property. When space neither expands nor contracts, however, there is no upper limit to the size of a region to which a single application of SR can apply.
     
  8. zanket Human Valued Senior Member

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    3,777
    Why?
     
  9. 2inquisitive The Devil is in the details Registered Senior Member

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    zanket,
    You do realize one of the main reasons why space is thought to expand is because proper motion of the distant supernovas and galaxies would indicate faster than light motion. How does an object travel over 13.7 billion lightyears in less than 13.7 billion years? How do you explain the difference between the distance to the type 1a supernovas calculated by redshifts and their distance based on apparant brightness? Remember, they are more distant than their redshift indicates. That is main reason why spacetime itself is thought to be expanding at an accelerating rate. The supernovas are too distant to be accounted for by proper motion without violating the speed of light even based on their redshifts. When the distance to the supernovas is calculated by their apparant brightness, they are even farther away than their redshifts indicate. Thus, spacetime itself is theorized to be expanding and the difference between redshift and apparant brightness of the 'candlesticks' indicate that expansion is accelerating. Observation throws a monkey wrench in your speculation. I don't think many physicists wanted the universe to be this way, but observation and measurement has been carried out very carefully and distances have been estimated by many different methods by cosmologists and astronomers, not just based on 'redshift' alone. The non-intuitive results demanded thorough and repeated measurement of distances. All point to the same result, faster than light expansion, everything beyond the Hubble sphere is moving away from us at a speed greater than the speed of light. Extensive knowledge is required to understand how we can 'see' light from objects that are receeding from us at greater than light speed. I have repeatedly read the explanations, but I lack the education to understand it completely, it is not simple. Proper motion alone cannot account for this expansion.
     
  10. zanket Human Valued Senior Member

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    3,777
    It does that in the same way it does in SR and GR, without space needing to expand. Hereafter let all distances be proper lengths, which are invariants; all observers agree on them. In SR, I can put any number of light years between me and my starting point, in an arbitrarily short time elapsed on my clock. The equivalence principle lets that behavior be applicable to planets. It shows that either of two planets initially right next to each other can put any number of light years between them in an arbitrarily short time elapsed on a clock on its surface. I give a simple proof of that in a simple solution to the flatness and horizon problems.

    SR and the equivalence principle demand that we observe high-redshift objects (like these supernovae) to accelerate away from us, even across regions of curved spacetime. I prove that in section 7 here. (And no, I do not apply SR to curved spacetime.) Neither dark energy nor expanding space is needed to explain this observation. It could be observed even locally, like in a lab.

    Regardless how many light years an object recedes per year on an observer’s clock (and that number of light years can be arbitrarily high), nothing need move faster than c as directly measured. Just as nothing need move faster than c as directly measured when, for example, I travel to the Andromeda galaxy, putting two million light years between myself and Earth in, say, 30 years on my clock, in which case the Earth recedes by two million light years in 30 years as I observe. And I will observe the Earth to accelerate away from me even as I decelerate relative to it as directly measured, as I prove in the link I gave above. As I decelerate relative to the Earth as directly measured, I will observe the Earth to accelerate away from me for the same reason we observe those supernovae to accelerate away from us; or at least there’s no need to believe otherwise.

    The problem lies not with the observations. The problem lies in the interpretation of them. When one looks at the whole picture, peculiar motion alone, where all velocities are <= c, does account for all of our observations.
     
  11. 2inquisitive The Devil is in the details Registered Senior Member

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    3,181
    zanket,
    Then you are not speaking of relativity theory if all observers agree the length, or distance, between objects does not vary from one frame of reference to another.
    No you cannot. You are simply mixing reference frames. Light will always travel one lightyear in one of your local clock's years. You cannot equal, or exceed, this distance if you are speaking of relativity theory. A lightyear varies by frame of reference, all observers do not agree on the physical distance.
    No, if one year elapses on the surface clock, the observer holding that clock will measure the distance to the other planet as always less than one lightyear, regardless of their relative velocity, according to STR.
    The equivalence principle has nothing to do with redshifts due to motion. It was the erronous assumption that a frame in freefall and an inertial frame in vaccu were equilavent. A clock in freefall will slow as it moves closer to the source of gravitational acceleration, while a clock in an inertial frame will not slow due to location. Also, a clock undergoing acceleration due to increasing velocity will not slow due to g-force alone if it does not change location in the local gravitational potential. This has been proven in particle accelerator experiments.
    You prove no such thing in your section 7. You speak of a rod ten lightyears long in your argument. Ten lightyears long according to which frame? In the rod's rest frame, it could be said the proper length of the rod was ten lightyears if it were measured by a light emitted at one end, reflected off a mirror on the other end, and then back to the emitter's location. It would take 20 years to measure the rod by that method, or 10 years if the emitter were located in the center of the rod and emitted light to mirrors on each end. But how would one know the center of the rod to begin with? If the length of the rod were measured by an observer moving relative to it, the measured length would vary according to the observer's local clock tick rate.
    You also stated the rod would 'break' due to stretching by expanding spacetime. Not true, the rod would break if connected to two stars which were increasing distance between them through proper motion, not expanding spacetime.
    My take on an accelerating rate of expansion? It is due to the permittivity and permeability of spacetime changing as the universe increases in volume. As the spacetime 'aether' decreases in density due to the expansion, the local speed of light increases. The wavelength of light is 'stretched' as it moves through less resistance (the permittivity and permeability of the vacuum) and at an increasing speed relative to 'c' (lightspeed) in the early universe. Gravity also increases the density of the spacetime aether, slowing light and atomic clocks relative to a clock located in an area of spacetime with less density. JMHO.
     
  12. zanket Human Valued Senior Member

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    3,777
    All observers, regardless of their frame, agree on a proper length, and this is a term of relativity theory. A proper length is an invariant quantity because it is measured in a specific frame, not necessarily an observer’s frame. See the link. Below I’ll use the term “proper distance” where it's more appropriate than "proper length". (For example, light travels a proper distance of one light year as it traverses the length of an object whose proper length is one light year.)

    Yes, I can. It was given that all distances are proper distances. I specified the frame for elapsed times. Light may travel a proper distance of more than one light year in one year on my clock, as I proved in the link I gave above. A proper distance of one light year does not vary by frame; a proper distance is an invariant, and “invariant” implies “does not vary by frame”. I did not mix frames; that is impossible when each measurement is mentioned individually as I did. (Just because two measurements are mentioned in the same sentence does not mean that frames were mixed.)

    Here’s another example: The proper distance between the Milky Way and Andromeda is two million light years. Let it take five million years on a clock on Earth for a rocket to travel from Earth to Andromeda and back. In the frame of some hypothetical planetary observer X somewhere in the Milky Way, can the elapsed time for the rocket’s entire trip be only one year? Sure, GR allows that via gravitational time dilation. All that’s required is for X’s clock to run at a rate that is one five-millionth of the rate of a clock on Earth, and gravitational time dilation allows such a difference in clock rates. Then in X’s frame the rocket can make its entire trip, including its recession all the way to Andromeda, in one year. The rocket could even pass X going out and coming back; both of those passes would occur within the same year on X’s clock. So I have proven that in principle there’s no upper limit to the proper distance an object can recede from a planetary observer in a given elapsed time in the observer’s frame.

    No, not when that distance is a proper distance, as I proved. Try to refute it if you want.

    Are you disputing the equivalence principle? If so, that’s okay, but you should start a new thread for that. In this thread I assume that the equivalence principle is valid.

    I say “proper length of ten light years”. The qualifier “proper length” indicates the frame.

    The rod’s proper length is a given, in which case its measurement is unnecessary. That said, the rod could be a ruler. Then you can just look at the last value marked on it to measure its proper length.

    It would vary according to the observer’s velocity relative to the rod, or according to the ratio of the rate of the observer’s clock to the rate of the rod's clock. But all observers agree that the rod’s proper length is ten light years.

    Your viewpoint is refuted here. Expanding space can rip apart even atoms under some hypothetical scenarios.

    I do prove it. You haven't refuted my argument.
     
    Last edited: Dec 24, 2006
  13. 2inquisitive The Devil is in the details Registered Senior Member

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    zanket, did you read your own reference (wiki)? Here it is for you:
    Did you notice the qualifier at the end "in a frame of reference in which the events are simultaneous"? Do you understand what that means? Proper lengths are invarient only within the frames in which the object (your rod) is at rest. A rod ten lightyears long will measure ten lightyears long in any frame in which the rod and the meter stick are at rest with respect to each other. The rod will not measure ten lightyears in length when measured from a frame with relativistic motion with respect to the rod. You cannot measure the proper length of an object that is moving relative to your meter stick.
     
  14. Alva Urbanus et instructus Registered Senior Member

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    163
    "I do prove it. You haven't refuted my argument."

    To an extent. Really you've just entered a document for peer review, in which I would have to disagree. The more you prove something, only limits the factors of what can disprove it. But it doesn't in any way mean you've proved anything. Calm down a little bit, and try emphasizing on various points as to clear up any particular subject you haven't covered. Then you can begin working a more structured defense, and even morph your hypothesis to a more fitting conclusion. While also try keeping in mind, some people will write an hypothesis for years before entering it for peer review. Because it's only natural for there to be some critical errors some where in your entry.
     
  15. zanket Human Valued Senior Member

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    3,777
    It is true that a proper length must be measured in that specific frame. But you're missing a subtlety here. A proper length is invariant for everyone. That’s what invariant means. Everyone agrees on a rod’s proper length, whether or not they can measure that length themselves.

    Yes, but that is irrelevant to my argument. I said:

    Now, when they come to rest relative to it, they are not in motion with respect to it, are they? Then when they measure its length at that moment, they measure its proper length. The beacon is at the other end of the rod, and they passed it a year ago on their clock, so it must have receded to a distance of ten light years (as they measure) in that time.
     
  16. zanket Human Valued Senior Member

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    3,777
    When the factors are limited down to “none”, something has been proven. Given the axiom a = a, can I prove that x = x? Yes I can.

    Not when the proof is extremely simple, like mine is.
     
    Last edited: Dec 24, 2006
  17. 2inquisitive The Devil is in the details Registered Senior Member

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    3,181
    zanket,
    Yes, an observer can only measure the rod's proper length while the observer is at rest wrt the rod. That measurement will differ when measured by an observer in motion wrt the rod, it's relative length.
    Yes, once the relativistic rocket comes to rest with respect to the rod, they will measure the rod's proper length. Your misconception is that the beacon changes it's physical location with respect to the rocket. It does not actually 'recede' from the observer. As the relativistic rocket slows to become stationary wrt the rod and beacon, the tick rate of its clock increases. When a relativistic passes by a rod without changing its velocity, it will measure the rod to be less than 10 lightyears in length because its local clock is beating slow. The distance between the beacons will measure less because that distance is a product of the observer's relative velocity multiplied by the same observer's local clock duration between seconds, days, years, etc. The relativistic rocket can transverse the distance between the beacons in less ten years because the rocket's clock is beating slow in the rod's rest frame, the frame in which proper distance is measured. The relativistic rocket can transverse the distance between the beacons in the rocket's rest frame because it is measuring the relative distance between two points in motion based on that frame's clock and meter stick. The common misconception is that the universe contracts and expands like an accordion as an observer changes his velocity with respect to the rest of the universe. That doesn't happen, his clock beats at different rates leading him to measure distances differently when those distances are based on 'c'.
     
  18. zanket Human Valued Senior Member

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    3,777
    You’re repeating yourself now. I haven’t disagreed with this, but neither have you used it to show a problem with my arguments.

    It does recede from the crew, or else the dictionary is wrong. Do you think that when I drive away from my house that the house does not recede from me? Relativity applies to that situation too.

    None of this affects my conclusion that “they observe the beacon recede to a distance of ten light years in one year”. Nor does it affect my proof that high-redshift objects must seemingly accelerate away from the observer, just like we observe about supernovae.

    There’s no misconception there. He measures distances between objects to be different than the proper distance between them because the space between them length-contracts and length-expands (uncontracts from a length-contracted state) as he changes his velocity relative to those objects. There is no one true measure of distance between objects. The distance in his frame is the distance he measures, and that distance has physical meaning for him; e.g. it can mean that he can traverse the distance in a shorter time on his clock.
     

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