Comments on: Lorentz invariance and you

By: LAWS OF PHYSICS STILL CONSTANT |

LAWS OF PHYSICS STILL CONSTANT | — Fri, 02 Oct 2009 11:24:50 +0000

[...] in the universe. It may turn out that violations of Lorentz invariance in the early universe might solve this second issue. However, such a violation in the earliest moments in the universe would not violate the biblical [...]

By: Forrest Nobles Pushing Gravity - Page 13 - Bad Astronomy and Universe Today Forum

Sun, 08 Feb 2009 19:10:36 +0000

[...] "is a cornerstone of relativity (and thus of all of modern physics)", to quote Sean Carroll, so forrest is quite right in saying that if his proposed experiment gave a non-null result, it [...]

By: Ripples in the Aether | Cosmic Variance | Discover Magazine

Ripples in the Aether | Cosmic Variance | Discover Magazine — Mon, 08 Dec 2008 06:55:58 +0000

[...] field theories. Instead of a light-carrying medium, we are interested in the possibility of a Lorentz-violating vector field — some four-dimensional vector that has a fixed non-zero length and points in some direction [...]

By: The Screwy Universe | Cosmic Variance

The Screwy Universe | Cosmic Variance — Wed, 31 May 2006 16:38:36 +0000

[...] Clearly important stuff. But for George and me this hit particularly close to home, as we had previously collaborated with particle theorist Roman Jackiw on a very similar-sounding project, looking for gentle rotations in the polarization of distant sources (and not finding any). In fact, this work with George and Roman was the topic of my first published paper. Our motivation was to test Lorentz invariance by searching for the effects of a constant vector field spread throughout spacetime. It turns out that such a vector can couple to ordinary electromagnetism, but only in certain specified ways. We showed that, if the vector pointed mostly in the time direction of spacetime, its effect would be to uniformly rotate the observed polarization of distant radio sources; we then searched for such an effect in the existing data, and didn’t find any. My job as the beginning graduate student was to look in the literature for measurements of the polarization angles and redshifts of as many galaxies as I could find. I managed to scrape up 160 such galaxies, which was enough to put a good limit on the effect we were looking for. (I should say that, as a nervous beginning graduate student, George was extremely intimidating because of his formidable intellect and amazing accomplishments, but in other circumstances one would recognize that he was extremely gentle and easygoing. Roman, on the other hand, was intimidating, period. But also fantastically smart, and an excellent collaborator once one calmed down and got into the science.) [...]

By: Chris W.

Chris W. — Wed, 26 Oct 2005 21:53:21 +0000

There is some recent work that indicates (independently?) that large* violations of Lorentz symmetry are a feature of generic renormalizable field theories that change the structure of spacetime at the Planck scale, posing another kind of fine-tuning problem. This paper reports a result that suggests that supersymmetry may have a role to play in suppressing such violations (thus avoiding the need for fine-tuning). Its citation links are worth looking at as well. (* inconsistent with current experimental limits)

By: Elliot

Elliot — Wed, 26 Oct 2005 16:03:44 +0000

Sean, thanks for the clarification. Intuition (particulary laymans intuition) is easily subject to error.

By: Sean

Sean — Wed, 26 Oct 2005 15:08:33 +0000

Subodh, you’re right that I didn’t really go into motivations. Non-commutative geometry would be one, but not what we were considering in our recent paper. There are some hints that effects in string theory or loop quantum gravity might give rise to Lorentz violation, but nothing very firm. But you don’t need anything very esoteric to get a nonzero vector field, at least temporarily; if you have a scalar field rolling down its potential, its gradient defines a nonvanishing vector field. So we were open-minded, not worrying about the origin of our fields at this point.

By: Sean

Sean — Wed, 26 Oct 2005 15:05:11 +0000

Elliot, as far as we know there is no such thing as the edge of the universe, or the center. And by “as far as we know” we mean more than “that’s our best guess”; we mean that all the data we have indicate that the visible part of the universe is smooth and uniform, it doesn’t have any special points either inside or somewhere outside. Of course we are allowed to speculate about what happens outside our observable patch of spacetime, but it doesn’t affect what happens inside.

By: subodh

subodh — Wed, 26 Oct 2005 07:12:16 +0000

hi sean… i noticed in your post that there is no mention of spacetime `non-commutativity’ as a potential motivation for studying the effects of violations of lorentz invariance. Is what you are proposing completely independent of this line of thought? If so, what might be other (theoretical, and not neccesarily phenomenological) motivations for violating lorentz invariance?

By: Plato

Plato — Wed, 26 Oct 2005 06:25:39 +0000

I think one had to understand what increasing complexity means in our universe? What relation to "time" would have been of value here, while pointing to the quantum levels?? We knew there existed "a time" for such things to emerge?