- #26

Vanadium 50

Staff Emeritus

Science Advisor

Education Advisor

- 27,578

- 11,776

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter Smattering
- Start date

- #26

Vanadium 50

Staff Emeritus

Science Advisor

Education Advisor

- 27,578

- 11,776

- #27

Buzz Bloom

Gold Member

- 2,405

- 441

Hi Vanadium:Neither is calculable today

Does this mean that the values were once calculable, but now they aren't? If so, can you explain why that might be so? If not, please clarify?

Regards,

Buzz

- #28

mfb

Mentor

- 35,647

- 12,214

- #29

Buzz Bloom

Gold Member

- 2,405

- 441

Hi mfb:

If that is the case, where did Michael Dine get his numbers? Were they just made up to make a point about how the Higgs mass seems to have a "magical" quality?

Regards,

Buzz

- #30

mfb

Mentor

- 35,647

- 12,214

Googling the number directly leads to Michael's talk.

- #31

Buzz Bloom

Gold Member

- 2,405

- 441

Hi mfb:All those digits? Sure. We know the magnitude of the number, but not the precise value.

Googling the number directly leads to Michael's talk

Thanks for the link and the Google hint. Both PDF files look both interesting and difficult. It will no doubt take me a while to digest whatever I can get out of them.

Regards,

Buzz

- #32

haushofer

Science Advisor

- 2,548

- 949

- #33

atyy

Science Advisor

- 14,672

- 3,137

http://quantumfrontiers.com/2013/06/18/we-are-all-wilsonians-now/

"Wilson’s mastery of quantum field theory led him to another crucial insight in the 1970s which has profoundly influenced physics in the decades since — he denigrated elementary scalar fields as

Susskind, channeling Wilson, clearly explains a glaring flaw in the standard model of particle physics — ensuring that the

- #34

atyy

Science Advisor

- 14,672

- 3,137

- #35

atyy

Science Advisor

- 14,672

- 3,137

- #36

- 170

- 21

Bothdark energy(another fine tuning problem) and the absence so far of new physics beyond the HIggs boson at the LHC are prompting some soul searching about whether naturalness is really a reliable criterion for evaluating success in physical theories. Could Wilson have steered us wrong?"

Is naturalness anything else than a pure aesthetic argument? Why should we expect nature to be elegant?

- #37

- 2,077

- 398

Is naturalness anything else than a pure aesthetic argument?

No, it is not. We have examples of theories with fine tuning being superseded by theories without one.

Give me a case where the opposite happened, if you know one.

- #38

atyy

Science Advisor

- 14,672

- 3,137

Is naturalness anything else than a pure aesthetic argument? Why should we expect nature to be elegant?

There is some aesthetics to it, but not the one you wrongly believe motivates it. The aesthetics is that we assume that our theory is not the final theory. Within that framework, naturalness can be technically phrased. See slide 8 of http://www.slac.stanford.edu/econf/C040802/lec_notes/Lykken/Lykken_web.pdf.

- #39

mfb

Mentor

- 35,647

- 12,214

- #40

ohwilleke

Gold Member

- 1,731

- 571

It turns out that this slight discrepancy arises in QED from interactions with virtual photons, and that if your theory doesn't allow for virtual photons (and other odd assumptions of path integrals like inclusion of photon paths at slightly more and slight less than the speed of light "c" even though those paths are highly suppressed) that you get an answer different from the physical one. The notion would be that fine tuning if it is observed must exist because we are missing something of the same sort of mathematical character as the inclusion of virtual photons in our theory which is why our expectations are so off. The search for why g-2 was fine tuned produced theoretical progress. Now, I can't say that the intellectual history of that discovery really establishes that fine tuning was the insight that really made the difference in figuring out that virtual loops needed to be considered in QED (and the rest of the Standard Model as well), but it is a historical example that captures the notion.

- #41

- 2,077

- 398

An example of fine tuning would be a theory where two large free parameters interact (subtracted, divided, etc) to give a vastly smaller number.

Before QED, no theory at all explained electron's anomalous magnetic moment. (I'm not sure we even had a theory or any kind which was predicting the value of electron's magnetic moment, anomalous or not).

- #42

mfb

Mentor

- 35,647

- 12,214

- #43

Vanadium 50

Staff Emeritus

Science Advisor

Education Advisor

- 27,578

- 11,776

- #44

Haelfix

Science Advisor

- 1,957

- 223

$$M_{observed}=M_{bare}+\frac{e^{2}}{4\pi \epsilon r_{e}}$$

Experiment sets a limit on the the size r so that the self energy was greater than 10 GeV and thus the first bare term must be chosen to cancel the second self energy term with a finetuning at about the O(.001) level

.511Mev=-9999.489+10000.000 Mev

Of course quantum mechanics comes to the rescue to 'explain' this finetuning, by adding the positron and the related quantum electrodynamic symmetry. This sort of picture is sort of the conceptual equivalent to explaining the Higgs mass by something like Technicolor.

- #45

king vitamin

Science Advisor

Gold Member

- 485

- 240

It actually is a good example of fine tuning, because Dirac left out a term for "simplicity." The so-called "Pauli term"

[tex]

\kappa [\gamma_{\mu},\gamma_{\nu}]F^{\mu \nu} \psi

[/tex]

can be added to the Dirac equation for arbitrary [itex]\kappa[/itex], which makes the magnetic moment an adjustable parameter while satisfying all necessary symmetries. It's actually Wilson who saves us here: this term is non-renormalizable, so it's irrelevant at low energies, giving us Dirac's universal result. It's not a near-cancellation scenario like the cosmological constant or Higgs mass, but Dirac did "fine-tune" [itex]\kappa[/itex] to zero.

Share: