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Expansion? Contraction?

  1. May 11, 2003 #1
    This is a thread about physics law.

    Physical laws are supposed to be invariant under choice of metric units. The meter and the second, for instance, are arbitrary choices.
    If we had come upt with other units of measurements, the physical laws would be the same.

    But as to how far can this be stated.

    Suppose something very unordinary. We had choosen our unit of length to be the distance between us, and a far away galaxy cluster.
    In old units, this galaxy system is about 5 billion lighthears away.
    Don't worry about the fact that such a choice would be rather unpractical. We only hypothetize and theorize.

    Suppose we would define that as our unit of measurement. Would all physical laws still be the same?

    If so, the please explain why all kinds of matter seems to be contracting on the long time scale...

    Is physical law invariant for all units of measurement?
    We suppose for instance that things like atoms, don't change in size.
    But how can we know that?
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  3. May 11, 2003 #2


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    Sure, if we pick a dumb unit, it'll be violated by physics. But physics doesn't depend on such choices; c, h and G aren't values we picked but values we try our best to measure.

    Look at Temperature. The common systems, Fahrenheit and Celsius, have zeros that don't really mean anything. They're derived from the uncontrolled behavior of water at unspecified environmental conditions. But the absolute or Kelvin scale respects the physics by setting its zero at the state of zero energy. Temperatures in F or C aren't physically invariant, but temperatures in K are.
  4. May 11, 2003 #3


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    just a quibble, SA,
    in the SI metric system it is impossible to measure the speed of light in vacuo
    because indeed the value for it (299792458) is a "number we picked"

    I think you know this but since the value of c USED to be based on measurement were just simplifying for the other poster.

    Also a similar change is in progress for h
    You know that if you go to the NIST website to get the
    "CODATA recommended values of the fundamental constants"
    Well, the ex-chair and current chair of CODATA are
    Mohr and Taylor of the NIST. they have recommended
    redefining the kilo by declaring an exact value of h.
    A preliminary resolution has been passed by CGPM
    the international body controlling SI. So there is a move
    on at the highest level to make it impossible to measure h just
    as it is impossible already to measure c.
    This has great advantages.

    And it has a remarkable similarity to what is done in physics
    textbooks where the units are defined by setting c=hbar=1
    or in theoretical papers where Boltzmann k is included and
    units defined by setting c=hbar=G=k=1

    The dominant system, SI, is beginning to resemble the system used by many in the physics community in the sense that
    the values of the basic constants are "numbers we picked".

    The only difference begin that in SI the emerging numbers are the messy result of historical accident (like 299792458) and in theoretical physics units the numbers or mostly just ONE.

    Here is a URL to one of Peter Mohr and Barry Taylor's articles which happens to be online in the Electronic Journal of Differential Equations

    http://ejde.math.swt.edu/conf-proc/04/m1/mohr.pdf [Broken]

    An even better paper is in the April 2001 IEEE Transactions
    on Instrumentation and Measurement, but this unfortunately is not available online.

    I am curious about what heusdens says:
    "Physical laws are supposed to be invariant under choice of metric units. The meter and the second, for instance, are arbitrary choices.
    If we had come up with other units of measurements, the physical laws would be the same.

    But as to how far can this be stated."

    Actually what freedom do we have in chosing units???? It is a good question! Physical law should be unchanged, and this poses a logical restriction on our choice. We are not allowed to choose a yardstick that is continually growing (like the distance to a certain galaxy, he says). But growing in what sense? Relative to what? I think probably relative to the planck length
    sqrt(hbarG/c^3). If we want physical laws to be the same in our new system then the new length unit must not be expanding or shrinking relative to sqrt(hbarG/c^3). heusdens! is this the kind of answer you want? SA, is this correct? at least is is one logical critierion that excludes the gradually expanding yardstick which heusdens offered as a test.
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  5. May 11, 2003 #4


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    This was just a small part of your question, but please explain the "contracting on the long time scale" part...(?)
  6. May 11, 2003 #5


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    Labguy altho you asked heusdens and he properly shd answer I would like to guess his meaning:

    if you measure with a yardstick that keeps growing (albeit slowly)
    then your distance figures for sizes of things that are not
    growing along with the yardstick will keep declining

    so compared with the yardstick, they are contracting (albeit slowly)

    his original idea was to take the distance to a galaxy as
    a yardstick, one which would grow with the general expansion

    so the sizes of our own galaxy and solarsystem and atoms etc,
    which do not grow, would appear on his scale to actually shrink.
  7. May 13, 2003 #6
    In our normal units of measurement, we conclude that the distance between earth and some distant galaxy system increases in time. This is just what the Hubble law states.

    I hypothese that suppose we had stated that our measuring unit would be the distant to that distant galaxy. Then by definition the distance to that galaxy system would equal 1, at any time.
    Yet, then we have the 'problem' that for instance the sizes of atoms, and so, would tend to shrink, since they were in the past larger.

    This conclusion is of course based on the fact that in the normal unit, the distance to the distant galaxy was said to increase, and in the new measuring system, it is a constant, which implies then that all sizes on the small scales, which in the normal measuring units are constant, must be contracting (atoms, etc).

    My question is then:
    1) Is such a transition from measuring units allowed? And if no, why not?
    2) If it is allowed, then explain the 'shrinking' effects in this new measuring unit system for all material objects (like atoms, etc).
  8. May 13, 2003 #7
    So, in fact your answer would be that, in contradiction to what physics normaly claims, there is an ABSOLUTE yardstick, which is the Planck length, and we can then only choose units of size, that are a constant times that unit, and not a unit that is not constant, relative to that yardstick.

    Still to me it is strange that nature has an absolute yardstick.
    This is a new feature of physics, physics used to be without absolutes.

    We could still doubt if the Planck length would be an ABSOLUTE.
    How would physics change if it is assumed that the Planck length is not a constant?
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  9. May 13, 2003 #8


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    There is some confusion. What I say is ordinary normal physics----not
    in contradiction to "what physics normally claims"---to the best of my knowledge.

    For physical laws to work you need an idea of measurement with an unchanging yardstick and other unchanging standards (of time, mass,...)

    If you measure with changing standards (like a yardstick that grows) then the "constants" that appear in physical laws will
    not be constant.

    This is why the tendency is (in modern systems of measurement) to choose a few quantities which people trust are constant and to anchor the units to them.

    1. in 1983 the meter was anchored to the speed of light
    by saying that the speed is exactly 299792458 m/s

    2. in 1990 electrical standards (the volt and ampere used for
    the most accurate measurement called V90 and A90) were
    established by anchoring them to hbar and e, in a similar way to (1).

    3. within the next decade it is expected that those in charge of the SI will redefine the kilogram by anchoring to a constant, either Planck's constant or the Avogadro number in a similar way to (1).

    The gradual anchoring of the world's units to the most trusted constants is being done by official international organizations like the CGPM
    (General Conference on Weights and Measures). I am not saying it is good or bad but simply pointing out that it is happening.

    You can very well ask "what if the electron charge e is changing???!!!" but you will be in the minority.

    You can ask "what if c is changing???!!!" but they have already anchored the meter to it. The consensus trusts the conventional constants for practical purposes of measurement. Indeed perhaps they are changing in some sense. But the conventional laws of physics treat c, hbar, G, e, Boltzmann k, etc as constant.

    Ultimately only systems of measurement in which the constants appear to be constant are considered legitimate.

    A convenient way to sum up the prevailing human idea of constancy is to say that a length unit does not change if it does not change relative to the METER, or, if you prefer something more fundamental, relative to the planck length.

    You do not have to consider either the meter or the planck length as "absolute", these are simply benchmarks of comparison to give meaning to the idea of invariance. Unchanging relative to what? Answer: relative to this or that.

    Your proposed yardstick of the distance to a galaxy which is drifting away from us in the Hubble flow (expansion of space) does not pass this test of constancy. The laws of physics would not work as usual with such units.

    Here is what I said earlier, and I hope this clarifies it:

    [[Actually what freedom do we have in chosing units???? It is a good question! Physical law should be unchanged, and this poses a logical restriction on our choice. We are not allowed to choose a yardstick that is continually growing (like the distance to a certain galaxy, he says). But growing in what sense? Relative to what? I think probably relative to the planck length
    sqrt(hbarG/c^3). If we want physical laws to be the same in our new system then the new length unit must not be expanding or shrinking relative to sqrt(hbarG/c^3). heusdens! is this the kind of answer you want? SA, is this correct? at least is is one logical critierion that excludes the gradually expanding yardstick which heusdens offered as a test. ]]
  10. May 13, 2003 #9
    I acknowledge your answer and see that it makes sense. It is not the problem as if that would not make sense.

    The thing is however, we treat certain things as constants, because they are constants in the unit system we choose. And we choose those units for good reason of course.

    My example of changing the yardstick for something else, that in the unit system we use, is not a constant, but changes in time, is only a way of theoretizing about this things.

    The only reason that would forbid us to take another measuring unit, was becase it would be of varying length IN RELATION TO SOME ABSOLUTE MEASURING UNIT. The Big question is then: does there exist in Nature an ABSOLUTE MEASURING UNIT, which is, something apart from what we DEFINE to be absolute?

    The speed of light, undoubtly, would be still constant in all measuring units. So, if we would define a new measuring unit for the length, which is acc. to the current yardstick varying, would make it necessary to redefine a lot of other measuring units.
    For instance, suppose we choosed the yardstick to be the distant to a far away galaxy. This new yardstick would then be constant in time.
    The old yardstick compared to the new yardstick would all decrease in length when time elapses. For the light speed still being the same, this would also mean the we would need a new unit for time.

    We know that the ratio of the new length unit in comparison to the old length unit is growing in time. The ratio of the new time unit in comparison to the old time unit, for the sake of light speed still be constant, would then also grow in time, in the same ratio as the length ratio's would grow.

    What would this mean in terms of contemporary theories, like for example the Big bang theory itself?
  11. May 13, 2003 #10


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    This is why many of our units are now being defined in terms of cosmological constants. The meter is defined from the speed of light now, not the other way around.

    For temperature, though the scales are (somewhate) arbitrary, they are attached to specific properties of water.
  12. May 13, 2003 #11


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    First of all, using examples of "us" and a distant galaxy is way too small when talking about the cosmological "measuring stick". I agree that we can use any unit we want, and can change them as convenient.

    But, I still do not see "ordinary matter" as shrinking just because of universal expansion. Use Plank Length, proton size, whatever. Just because other matter (the universe as a whole) seems to be expanding does not mean that our "basic" atomic, therefore matter, size is shrinking. What is changing is just distance and time. If we carry the previous arguements backward, does that mean that the first matter forming from the radiation-soup after the Big Bang were huge atoms / particles that were larger than the quarks / protons / atoms, etc. we see today. I don't think so.

    They were larger, at the time, only when compared to the scale of the universe, but the scale (distance) and time have changed to place any grouping of matter, galaxy for example, farther from another grouping of matter, but that doesn't change the "actual" and physical size of any particular particle if we could have measured it then vs. now.

    The discussion of universal expansion really only needs to deal with distance and time. I don't think we will later become very small people made of very small atoms.
  13. May 13, 2003 #12
    Well a distant galaxy can be in terms of comparable distance to the known, observable universe size.

    I am not suggesting that we ever should change our normal measuring units for length on the basis of cosmological distances.
    As far my story is concerned, I just ask anyone, to be prepared to hypothetize about another choice for the meter stick.

    You prefer to say that atoms don't shrink in the cause of time.
    That is of course our normal understanding of the situation, cause our length unit could not measure it. A measuring unit we have (wther that be meters or inches, or whatever unit) will always be in terms of fixed sizes of a specific atom size, no doubt about that.

    The actual underlying question is however, if there is any ABSOLUTE measuring unit available, that would prevent us from claiming for instance that, instead of the universe expanding in size, it is matter itself that shrinks in size.

    I was just theoretizing this issue, and as far as I understand it, if there realy is no ABSOLUTE standard for the length unit, we realy should be able of rewriting all of physical laws, by transforming our length units to conform a fixed size of the universe.
    What is necessary then is to find a physical interpretation why all forms of matter shrink in size, IN TERMS OF THIS NEW LENGTH UNIT.
    Which is of course the same as finding a physical interpretation for the fact that all of space expands, IN TERMS OF THE CURRENT LENGHT UNITS.

    Wether something shrinks or expands, can not be stated ABSOLUTELY, but only RELATIVELY, if there is no such thing as an ABSOLUTE LENGTH UNIT.

    I know that this all sound some weird, cause we are too used to the normal length units, but provided that there realy is no absolute length unit in Nature, I can't see a reason why this could not be done.

    As for your imagination, and for interpreting known things in a different way, but with the same outcome, I advise you to read this hypothese about an alternative explenation to gravity (https://www.physicsforums.com/showthread.php?s=&threadid=846") which does not explain gravity as an attractive force that all masses excert upon each other, but as a pulling force that acts on all matter by surrounding space, which shows up that because of the "shielding effect" that masses have upon each other, a net attraction occurs between masses.
    The beauty of the theory is that, although it is very weird in it's interpreation, the result that comes out of it, in numerical terms, is the same laws of gravity as we are used to.

    In more or less the same way, Einstein understood that mass and curvature of space in fact are equal.
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  14. May 13, 2003 #13
    Some side note:

    The laws of physics are UNCHANGED, regarding whatever measuring units we have. Cause the LAWS OF PHYSICS are just describing the material reality that exist OUTSIDE and INDEPENDEND of our minds. If our minds would choose a different measuring unit, this does not cause the universe to work in another way.

    What can change is however, that all kinds of formula's, that is the mathematical notations we have to describe how the laws of physcis work, would have to be worked out in a different way.

    But they would still describe the same physical reality.
    Physical reality does not change because we change our way of perceiving the reality.
  15. May 13, 2003 #14
    Please bear in mind that all notions we have of "huge" and "small" are all RELATIVE notions.
    Independend of what our measuring units are, we can state that the size of atoms, as compared to the size of the universe, was billions of years ago larger, then they are now.
    If we state that the size of the atom is taken as being constant, then of course we interpret that the universe became larger. If we however would choose the universe to be of a constant size, it would mean that the atoms became smaller.

    It's all RELATIVE.
  16. May 13, 2003 #15


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    I agree 100%. That is exactly what I was meaning, and I guess you too. It is a tendency for some to "overcomplicate" it or "overtheorize" it to the point where we are not in physics, but in metaphysics. For this, there in no, one exact answer, and many different explanations will all be correct from the assumptions used at the time.

    Last edited: May 13, 2003
  17. May 13, 2003 #16
    Is your last statement an indication you were not sure on this??

    Anyhow -- when theoretizing about this new set of measuring units -- what about:
    - the shrinking of atoms
    - the new time unit (what would be the age of the universe? Presumably infinite?)

    Or is it assumble that this shift in measuring units can not be allowed? And why? Because there is an absolute unit of measurement after all?
    Last edited: May 13, 2003
  18. May 13, 2003 #17


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    (1) No, I feel quite sure about this.

    (2) I don't believe atoms are shrinking, just distance and time are changing. A "standard" of distance measurement are many we make up for convenience. If there is a standard, it would be Plank Length or perhaps the effective range of Gauge Bosons.

    (3) Why would we need a new time unit?? We have quite a few ways for measuring time as it is, again all created for our convenience or ease of understanding. The age of the universe would be no more or less than the 23 theories bantering around now, usually from 12.3 billion years to infinite in a few, unfavored, theories. It
    may be infinite later, but from beginning to the present is finite for sure.
  19. May 14, 2003 #18
    Neither do I believe atoms are shrinking. It is not a matter of belief, it is a matter of measurement. And measurement involves a defined meter stick. And we know that in our normal measuring units, atoms don't shrink.
    But this does not contradict the fact that if the alternative meter stick (size of the observable universe or so) were in coherent expansion with the expansion of space, that is, in such a measuring unit system, the size of space would then be constant, we nevertheless had to agree with that behavious of atoms too.

    My post is not about need. For sure we don't need measuring units which are way too large for all practical purposes! I am not arguing for introducing new measuring units in physics, I am just theoretizing about the freedom of choise of measuring units.
    It's not about need, it is about theoretical possibility.
    The only possible outcome for it would be to have a different approach on the way the physical universe behaves.
  20. May 14, 2003 #19


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    Heusdens, we have a problem (I think)

    The expansion of time incriments to match the expanding units of spacial measure (expanding relative to our current method, that is) would not account for the redshift, would it? I mean, it's all well and good to say that the distance to gallaxy M-86 is constant at one thousand light-year, and one year is the time it takes light to get from M-86 to Earth, devided by one thousand. But light from M-86 would be shifted slightly to the red. And more distant gallaxies would be even more shifted, even though they are all stationary relative to us (if measured by placing a bunch of "expanding" yardsticks end-to-end).

    Also, what would redshift be defined as? The number of light waves that reach your eye in a second? But if each second is longer than the last, this measure of frequency will constantly decrease.

    Additionally, if we chart the decay of a radioactive isotope (over time) we see a curve. This "expanding" time-unit also describes a curve when compared to our current way of measuring time. So for every rate of decay, there should be a mass at which the two curves match, yes? If so, we may have found our first constant under the new system of measure (Heusdens' Constant?).
  21. May 15, 2003 #20
    Re: Heusdens, we have a problem (I think)

    The nice feature of such a new "expanding" (as regard to our normal time units) time unit would be that the universe would have expaned for infinite time (new time units).

    It would be nice to think this idea completely through, which must be done with a professional physicist.

    I don't claim that this idea is original, because I have come across some similar ideas.

    I think the best way to portray this is that it is an extenstion to the Relativistic theory of Einstein, which is founded on the relativity of measurements (speed, etc), and is now extended to the measuring units as well.

    So "Relativistic Theory of Measuring Units" would be a good candidate name. I don't need to be honoured for bringing up an idea that alreay went around. the actual work lies in thinking and calculating this through all of know physcics laws.... Quite an amount of work!!

    The only argument so far I can come up against this theory, is that as some claim, Nature comes up with Absolute measuring units for time, lenght, mass, etc.

    I claim (same as physics has claimed until recently) that on the contrary, Nature does not contain such absolutes measuring units. All measuring units, even if they are not linearly related (unit in one measuring unit is a constant1 plus a constan2 times the other unit of measurement), should be regared equal. Same as motion is relative, also the measuring units are relative.
    For practical (earthly) purposes, our common units are certainly sufficient, and in no way I imply we should drop this measuring unit system. But when it comes to measuring things on a cosmological scale, and when encountering weird concepts such as "expansion of space" (how can space itself expand?) this might indicate we use improper measuring units. This also because it would imply a concept as a "begin of time".

    When we adapt the vision that space is 'constant' ,i.e. the measuring units are in conformance with the overall expansion of space, as argued from the point of view of the interpretation of the cosmological observation in the common units of measurement, and thus imply that large distances in space itself, are constant in time, we could have a different approach on the events that occured in the cosmos on the large time and length scales.
    It would imply firstly that:
    1) space itself and large distances in space, do not expand, but remain constant in time, when measured in the new length unit.
    2) the new time unit, because of the constant lightspeed, in ratio to the old time unit, would be proportional to the ratio of the new lenght unit to the old length unit.

    The conclusion from this would be that in the new time and length units, space itself would be of constant length, and time would not have a begin in a singularity.

    I do think that this implication is attractive, although a whole lot of physics has to be rewritten to accomodate for this change in measuring units. For exmple, we would need to explain from the point of view of the new length and time units, why all material forms (stars, planets, atoms, etc) are contracting in time.

    The question is of course: can that be done, without running in deep contradictions?

    Let us debate this idea some more then....
    Last edited: May 15, 2003
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