Consequences of proton size being smaller than thought to be?

  • Thread starter Thread starter olee
  • Start date Start date
  • Tags Tags
    Proton
Click For Summary

Discussion Overview

The discussion revolves around the implications of recent findings suggesting that the proton is smaller than previously thought. Participants explore potential consequences in both chemistry and physics, examining how this might affect various measurements and theoretical models.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express uncertainty about the validity of the findings regarding proton size, suggesting that if the results are accurate, they may not have significant chemical consequences due to the small effect size.
  • It is noted that nuclear size is typically treated as negligible in chemistry, with finite-size corrections being many orders of magnitude smaller than chemical energies.
  • One participant mentions that the discrepancy between theory and experiment is of greater interest to physicists, particularly in relation to quantum electrodynamics (QED) and the Lamb shift measurements.
  • Another participant questions whether proton size affects spectroscopy, specifically referencing the hydrogen Lamb shift and its dependence on the proton's charge radius.
  • It is discussed that while the proton size may affect spectroscopy, the effect is not typically measurable in ordinary conditions, and the accuracy of chemical measurements is generally lower than that of the Lamb shift calculations.

Areas of Agreement / Disagreement

Participants generally agree that the implications for chemistry are minimal, but there is ongoing debate regarding the significance of the findings for physics, particularly concerning QED and the Lamb shift. The discussion remains unresolved regarding the broader implications of the proton size discrepancy.

Contextual Notes

Limitations include the dependence on the accuracy of experimental measurements and theoretical models, as well as the unresolved nature of the discrepancies noted in the context of QED calculations.

Chemistry news on Phys.org
Well, we don't know for sure yet if that result is correct. But if we assume it is, the chemical effect? I can only assume you mean chemically, since this is the chemistry sub-board.

The answer to that is: No chemical consequences. It's too small an effect. Basically you don't need to take nuclear size into account whatsoever as far as chemistry is concerned. Usually it's treated as if it were infinitesimally small, and finite-size corrections are many orders of magnitude smaller than chemical energies. It's so small it couldn't even be measured accurately at all for an ordinary hydrogen atom. This result came from replacing the electron in helium with a muon.

For the physicists it's more interesting because there's a discrepancy between theory and experiment.
 
alxm said:
Well, we don't know for sure yet if that result is correct. But if we assume it is, the chemical effect? I can only assume you mean chemically, since this is the chemistry sub-board.

The answer to that is: No chemical consequences. It's too small an effect. Basically you don't need to take nuclear size into account whatsoever as far as chemistry is concerned. Usually it's treated as if it were infinitesimally small, and finite-size corrections are many orders of magnitude smaller than chemical energies. It's so small it couldn't even be measured accurately at all for an ordinary hydrogen atom. This result came from replacing the electron in helium with a muon.

For the physicists it's more interesting because there's a discrepancy between theory and experiment.

Thanks for the reply. The article says they used http://i38.tinypic.com/1zobuyq.png". Surely the proton size affects spectroscopy, does it not?
I'm interested in the fact that you mentioned that it's more interesting for physicists. I'm not debating, but I was wondering if you could explain why that is so.

I appreciate the reply.
 
Last edited by a moderator:
olee said:
The article says they used http://i38.tinypic.com/1zobuyq.png". Surely the proton size affects spectroscopy, does it not? I'm interested in the fact that you mentioned that it's more interesting for physicists. I'm not debating, but I was wondering if you could explain why that is so.

Right, meant to say hydrogen of course. Yes, it affects spectroscopy, but not enough that it can be measured, ordinarily. The measurement here is of the hydrogen Lamb shift, a very slight shift between the 2s and 2p levels of the atom. Which is an effect of quantum electrodynamics (vacuum polarization). Calculating it theoretically requires using the charge-radius of the proton. The muon is 200x heavier than the electron, so it's 200x closer to the nucleus and the effect of nuclear structure in its Lamb shift is correspondingly magnified. Here, they found a discrepancy - either the calculations which worked for hydrogen didn't work anymore, or the size of the proton was different.

This interesting for the physicists because the Lamb shift is an important test-case for QED. If the experimental results hold, then something is wrong with the QED calculations of the Lamb shift, and while I wouldn't go so far as to assume something's wrong with QED itself, it might mean there's some as-of-yet-unknown effect they haven't been taking into account.

Chemically it's not interesting because when you talk about an energy of chemical interest, such as the heat of formation of a molecule (even a simple one such as H2), then the experimental accuracy is lower (say, 7 decimals for H2, as opposed to the 10-12 decimals for the Lamb shift), and theory matches experiment without having to take QED effects into account.
 
Last edited by a moderator:

Similar threads

  • · Replies 12 ·
Replies
12
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 7 ·
Replies
7
Views
14K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
4
Views
6K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
4
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K