Is the mass of the electron constant?

  • #1
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If the mass of the electron has been changing during the evolution of the universe, then the orbits of the electrons would also change, which will shift the light spectrum of each atom.
Could this explain red shift of far galaxies, and the shift is not because the universe is expanding?

Henry
 

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  • #2
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Could this explain red shift of far galaxies, and the shift is not because the universe is expanding?

No. Besides, we have no reason to think that electrons (or any other particle) mass changes with time.
 
  • #3
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Do we have reason to think that it is, and was always, the same constant?
Is the acceleration of the universe expanding not a good reason to refresh our unproven postulates?

Henry
 
  • #4
Dale
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If the mass of the electron has been changing during the evolution of the universe,
The mass of an electron is a dimensionful constant, so you can simply define units such that it cannot change by definition or units such that it is changing by definition. There is no physical consequence to either choice of units.

For questions like this you need to find the relevant dimensionless constants.

the orbits of the electrons would also change, which will shift the light spectrum of each atom.
The constant which controls this in a physically meaningful way is the dimensionless fine structure constant. There have been extensive studies of possible variations over the lifetime of the universe. Any such variations are below the level of experimental detection. It cannot account for the observed red shift.
 
  • #5
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I fail to understand.
Changing of the mass of the electron is dimensionless (the mass has dimension, not the change).

Are there studies that such constants have too low changes to be detected?
How such studies could be made?
it must be calculated relatively to other constants, such as length or time, but what if all change?

Henry
 
  • #6
Dale
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Changing of the mass of the electron is dimensionless (the mass has dimension, not the change).
##\Delta m## has dimensions of mass. ##\Delta m/\Delta t## has dimensions of mass over time.

Are there studies that such constants have too low changes to be detected?
Yes, for the fine structure constant and probably other dimensionless constants.

How such studies could be made?
it must be calculated relatively to other constants, such as length or time, but what if all change?
That is why you need to use dimensionless quantities.
 
  • #8
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it must be calculated relatively to other constants, such as length or time, but what if all change?
If they change in such a way that the fine structure constant (and other dimensionless ratios) do not change, then all we've done is redefine the kilogram and our other units. All experiments will still yield the same outcomes, the needles on our dials will still point to the same places, chemistry and every else driven by the physics of orbital elections will stay the same, the energy levels won't change, ..... It's no different than doing physics using the old english units instead of metric.

To actually get something physical to change (for example, in the first post of this thread you asked about atomic spectra changing over time) one or more of the dimensionless ratios like the fine structure constant would have to change. Thus, your question is really about whether these ratios have changed over time, not the mass of the electron.

The issue here is basically the same as a question that is asked here much more often: Suppose the speed of light were to change? You might want to search out some of those threads; the discussion there will be more complete. Also, be sure to check out the recent redefinition of the kilogram; it will reinforce the essential arbitrariness of the numerical value of the masses we assign to particles. The physics is in the ratios between these values, not the values themselves.
 
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  • #9
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No. Besides, we have no reason to think that electrons (or any other particle) mass changes with time.
Shouldn't we rather say the electron's energy content does not change since when photons are emitted or absorbed, there is presumably a Δm = ΔE/c^2 change?

Edit: contradiction here since both are changing but then what property is it that doesn't change ?
 
  • #10
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Shouldn't we rather say the electron's energy content does not change since when photons are emitted or absorbed, there is presumably a Δm = ΔE/c^2 change?

Edit: contradiction here since both are changing but then what property is it that doesn't change ?
The property that doesn't change is the electron's rest mass, which is what we're talking about when we say "the mass of the electron" without further qualification. Rest mass and rest energy are equivalent, so we can go with "energy content" as you suggest; it's just the a matter of whether we use units like MeV or kilograms to specify it.
 
  • #11
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So now which electron has "rest" mass/energy: the one that (for eg) sits safely in Hydrogen's 1s orbital or the one that's energized sufficiently to become a 'free' electron?
 
  • #12
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If the mass of the electron has been changing during the evolution of the universe,

You need to, first of all, establish the validity of this statement. You need to show ample evidence to support it. This is before you start to consider the consequences of it.

Otherwise, you're asking us to explain why the unicorn has pink horn.

Zz.
 
  • #13
Dale
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Shouldn't we rather say the electron's energy content does not change since when photons are emitted or absorbed, there is presumably a Δm = ΔE/c^2 change?
This is precisely why a free electron cannot emit or absorb a photon. It must be bound in an atom. The mass of the atom as a whole increases or decreases according to the amount of energy emitted or absorbed. A free electron cannot do that since its mass cannot change, so all it can do is scatter a photon.

So now which electron has "rest" mass/energy: the one that (for eg) sits safely in Hydrogen's 1s orbital or the one that's energized sufficiently to become a 'free' electron?
All electrons have the same invariant (aka rest) mass. However, the mass of the hydrogen atom is slightly less than the mass of a free proton plus the mass of a free electron.
 
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  • #14
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Back to the future
When I asked about a change in the mass of an electron, it is the (mass after) / the (mass before) in some 2 points of time. This ratio is dimensionless.
If all other constants are also changed, does it means that the emitted spectrum stays unchanged?
Other constants must to be change at the same ratio, or the constant could be in power of something (f.e. meter is in power 2 in calculating the EM force).

Can we realty say something about all these constants, what define them? why are they constants? how did they behave during the evolution of the universe?

Henry
 
  • #15
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Back to the future
When I asked about a change in the mass of an electron, it is the (mass after) / the (mass before) in some 2 points of time. This ratio is dimensionless.
It is, but it also impossible to measure - you'd need to have last year's electron and this year's electron together at the time to measure that ratio, and that is clearly impossible.
The best you can do is to find the ratio of the electron mass to something else at one time, then at some later time see if that ratio has changed. For example the ratio of the proton mass to the electron mass is 1836.15267389, and if that were to change over time it would be a very big deal with clearly detectable physical consequences.

Suppose we were to find that that ratio is increasing over time (although all the available experimental evidence, and that's a very large amount, says that it is not changing at all). Does that mean that the proton mass is increasing or the electron mass is decreasing? That depends only on how we've defined the units that we're using; the physics is all in the dimensionless ratio.
 
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  • #16
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I think this thread has gotten tangled up in knots, or at least ratios of knots. (Look - a box of electrons from 1927!)

We can ask the question is there any atomic physics whatsoever that can fake the Hubble Law, and the answer is definitely no. We see redshifts of light apart from atomic spectra, light from blackbodies. We see time dilation in supernova and GRB durations - not an atomic process. And when we have multiple measurements from atomic and non-atomic processes, they agree.
 
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  • #17
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When I asked about a change in the mass of an electron, it is the (mass after) / the (mass before) in some 2 points of time.
Ah, ok. That is not what people usually mean when they say “change of x” which usually means ##x_{after}-x_{before}=\Delta x##.

So the proton/electron mass ratio is close to what you want. Not exactly, but what you are specifically asking about is not studied, for the reasons pointed out above. The proton/electron ratio is constant to the best of our measurements.
 
  • #18
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In order not to complicate things, I would like to stay in 2 fix points in time, so I look at the relative changes of constants, and not at the rate of the changes.

Let’s assume that the energy of the electron in the atom's orbit E ∝ me^4
The Hubble effects states not only the shift to red, but also that is it greater the farer the object is, which means the sooner it is after the bang.
It could be because of 2 reasons (at least), the Doppler effect, and the change in me^4 during the expansion.


I can understand how difficult it is to try to see the differences over time of me^4, but to look after the dark matter is also not a piece of cake (not to speak that both effects could contribute to Hubbel’s effect).
I can not understand the assumption that these constants were always fix, only because our time interval of measurements is too short to see differences.

Why the dark matter receives such a priority over changes of constants (which will better suit Einstein's first intuition) in astrophysics ?

Henry
 
  • #19
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Why the dark matter receives such a priority over changes of constants (which will better suit Einstein's first intuition) in astrophysics ?
All light, not just light produced by processes that depend on the energy levels of the bound electron, is red shifted identically. Thus, we'd need independent changes in multiple different and unrelated physical processes, and these ostensibly independent changes would have to each be of exactly the right size to produce exactly the same redshift over time. That's starting to sound a bit implausible.

Furthermore, some of these changes over time would have effects that are detectable in lab experiments. These experiments have been done (see the paper Dale cited in post 7 above, for example) and the effects have not been seen.

Thus, the change-in-constants hypothesis requires that we accept a series of remarkable coincidences and reject a substantial body of other evidence that shows the constants don't change. The dark matter hypothesis requires only that we accept the possibility that our telescopes aren't yet good enough to see everything that there is - not much of a stretch at all.

This forum has some threads on this "why dark matter?" question, and some of these go into much more detail about why dark matter is by far the most promising hypothesis. You might want to search some of them out for more on the subject.
 
  • #20
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Why the dark matter receives such a priority over changes of constants (which will better suit Einstein's first intuition) in astrophysics ?

Henry

When Einstein first developed GR it predicted an expanding universe. There's a common misconception that the expansion is due to dark energy. It's not. Even without dark energy (zero vacuum energy density) the universe would be expanding. Dark energy is responsible for increasing the expansion rate.

So, basically, if you want a static universe, you have to rework GR, or fudge it in some way.

There is no model of changing constants that fits the redshift data. And, there is no atomic theory that says why the ratio of proton to electron mass might be changing. So, basically, you have a "shot in the dark", that has no theoretical model to support it and it doesn't fit the available data in any case.

The dark energy model fits easily into GR and a constant vacuum energy density fits the data. That leaves the problem of explaining dark energy and the value of the energy density.

There's no comparison here between a solid theory with a piece missing and a wild speculation that has no theory or data to support it.
 
  • #21
Vanadium 50
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I miss the days when we didn't discuss personal theories on PF.

Henry, this proposal of yours requires no fewer than six new physics effects. You need three to explain the Hubble Law in three different physical phenomena (see my earlier message) and no fewer than three more to explain why the first three effects are hidden in other experiments and observations.
 
  • #22
Dale
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I can not understand the assumption that these constants were always fix, only because our time interval of measurements is too short to see differences.
Did you not read the paper I posted above? The validity of our assumptions is always a subject of scientific inquiry.

Why the dark matter receives such a priority over changes of constants (which will better suit Einstein's first intuition) in astrophysics ?
Because changes in those constants have been investigated and shown to be very small.
 
  • #23
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Thanks, I read the paper, but I could not understand if it proves that there were negligible changes in the beginning of the expansion.
One could think about changes in few parameters that leave constant what we are looking, but not the me^4.

Well, I understand that this possibility requires too many changes in the current theory, so it is not elegant enough in order to start and investigate it.
I hope we are not looking for the key under the street lamp, only because there is light there,
but of course we can not invest a lot of energy into any crazy direction.

Henry
 
  • #24
Dale
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I miss the days when we didn't discuss personal theories on PF.
@Henry_F I have to admit that I am starting to join V50 in his sentiment here. Your original question on variation of the electron mass has been answered. The ratio you are describing is not something that can be investigated, instead temporal variation in other dimensionless constants that are both directly relevant to the theory and experimentally accessible are investigated and found to not vary.

Furthermore, as has been pointed out, there is no plausible variation which can account for the observed redshift even in principle. Certainly, variation in the electron mass would not do it.

Do you have any specific question about the mass ratio investigated or any remaining confusion about why your specific ratio is not investigated?
 
  • #25
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I could not understand if it proves that there were negligible changes in the beginning of the expansion.
It does not. However, the observed redshift comes from times substantially after that.
 

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