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Proton-electron mass ratio; changed? how much?

  1. Nov 8, 2014 #1
    On the subject of our 'finely turned universe', I have read that the proton-electron mass ratio can not deviate more than 1:1037. In other readings, the allowable deviation was stated as 1% ("If the neutron were very slightly less massive, then it could not decay without energy input. If its mass were lower by 1%, then isolated protons would decay instead of neutrons, and very few atoms heavier than lithium could form."

    Scientists using a Effelsberg 100-m radio telescope have determined that the ratio has changed "by only one hundred thousandth of a percent or less over the past 7 billion years"; alternatively, the change is written as 10^-7.

    My question is: Is the change in the ratio (one hundred thousandth of a percent, 10^-7) greater or less than 1:1037?

    [1:1037 is 1:10 to the 37th power]
  2. jcsd
  3. Nov 8, 2014 #2

    Vanadium 50

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    I'm sorry, but that is simply not correct.
  4. Nov 8, 2014 #3
    Has the maximum deviation of the protron-electron mass ratio been calculated? If so, what is it? Is it something less than 1%?
  5. Nov 8, 2014 #4


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    Do you mean 1037 (one thousand thirty-seven), or 1037 which is a really really really big number, or 10-37 which is a really really really small number?

    (Tip: to write exponents correctly, highlight them with the mouse, then click the "x2" icon in the toolbar at the top of the message editor.)
  6. Nov 8, 2014 #5
    My lack of physics/math background is showing.

    The number would have to be small since the article I read was speaking on the subject of a finely tuned universe and how a slight deviation in the ratio would not support the creation of the universe as we know it.

    This would seem to be the equation, 1:10-37.

    Thanks, jtbell, for the tip.
  7. Nov 8, 2014 #6

    Vanadium 50

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    It's measured, not calculated. And it's known to half a part per billion - which is precise, but nowhere near as precise as your 10-37. Since it's not known to 10-37, it's hard to argue that it's value matters at the level of 10-37.
  8. Nov 9, 2014 #7


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    If you can still recall where you read it (something I often struggle with) post the specific reference and you will almost certainly get more help understanding what you read.
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