Their dead-heat finish strongly supports the Einsteinian view of space-time, researchers said. The wavelengths of gamma-ray burst photons are so small that they should be able to interact with the even tinier “bubbles” in the quantum theorists’ proposed space-time foam.
If this foam indeed exists, the three photons should have been knocked around a bit during their epic voyage. In such a scenario, the chances of all three reaching the Fermi telescope at virtually the same time are very low, researchers said.
So the new study is a strike against the foam’s existence as currently imagined, though not a death blow.
“If foaminess exists at all, we think it must be at a scale far smaller than the Planck length, indicating that other physics might be involved,” study leader Robert Nemiroff, of Michigan Technological University, said in a statement. (The Planck length is an almost inconceivably short distance, about one trillionth of a trillionth the diameter of a hydrogen atom.)
This is essentially a description of the zero point field which AFAIK is a proven fact inasmuch as the Casimir effect can be proven and even measured. So either that article is inartfully written or I’m missing something.
The ‘space-time foam’, as usually conceived, is a somewhat naive, qualitative picture going back to a discussion by Wheeler: if we think of the vacuum as containing virtual particle and antiparticle pairs that pop in and out of existence, then as we go to shorter and shorter length scales, those virtual particles get more and more massive. Thus, their mass will eventually lead to significant gravitational effects at microscopic scales. One possible effect of this is Lorentz-invariance violation, which would mean that special relativity ceases to work at high enough energy scales, one of the consequences of which would be a difference in speed for high energy photons.
There are some (more or less) independent lines of thought that lead to a similar conclusion, such as the loop quantum gravity inspired idea of ‘doubly’ or ‘deformed’ special relativity (where not only the speed of light in vacuum c, but also the Planck length l[sub]p[/sub] is supposed to be observer invariant). The results simply say that this difference in speed were not observed.
But we already know that there must be something wrong with the naive picture. The most striking demonstration of this is the case of the cosmological constant: observationally, there is a very tiny, positive cosmological constant, leading to an accelerated expansion of the universe. Now, trying to deduce this from the above picture runs into severe difficulties: if one just assumes an ‘infinitely divisible’ space-time, one arrives at a vacuum energy density that should be infinite. If one assumes a ‘cut-off’, a shortest length typically of the order of magnitude of the Planck length, one arrives at the fabled ‘worst prediction of theoretical physics’, a value of the cosmological constant that is roughly 120 orders of magnitude greater than observed.
So the problem here is with the naive quantum foam, particles popping in and out of existence type of thinking. And this is not terribly surprising: you essentially do two contradictory things when using this thinking. One is that you suppose quantum field theory applies—but QFT is only defined on a fixed background space-time. The other is assuming that general relativity applies, such that the mass of the virtual particles ‘warps’ the background space-time. Clearly, there’s some tension here: the space-time is both supposed to be fixed and wildly fluctuating. It’s generally thought that a theory of quantum gravity is needed to reconcile this tension.
And in order to find this theory, the observations reported on give an important guideline: it won’t be a theory that includes Lorentz invariance violations (or at least, they’d have to be much smaller than would be naively expected).
Some Gamma-ray bursts last short fractions of a second, and their spectra varies over that time span. So if you take photons that are close together in energy, you can probably get a pretty tight-bound on when they were emitted (that probably also explains why there were so few photons in their sample).
Very important distinction, here: The Casimir effect as generally understood is due to virtual particles within spacetime, but the spacetime itself is smooth. What’s being discussed here is the possibility that spacetime is itself composed, somehow, of virtual particles. The former is about as well-understood as anything in science, while the latter is about the most poorly-understood concept in science.
I see the distinction and why the two would be confused so thank you. However I’m not sure how much sense it makes to speak of the fabric of the universe having time as an integral element and at the same time saying that fabric is composed of what amounts to a constant exchange of matter and energy - which is essentially what you’re talking about if you envisage the zero point field as being virtual particles and anti-particles arising ab nihilo and then annihilating back into nothingness.
edit: and I think I understand that zero point field as a term of art would only apply to quantum mechanics operating WITHIN space time, so forgive the loose use of terminology.
One should never cross the font streams when discussing quantum mechanics but if absolutely essential to save one’s pocket universe I would strongly recommend the EN-biggen technique rather than the less refined EM-biggen approach.
Justification: I’ve taken to it, and use it conventionally, to make distinctive by size and font longish quotations, and to save screen space. The font is at standard (here) “2”, larger than the reduced sans-serif here (another easily identified difference of the font I use), which makes it simple.
It’s a combo of “indent right” and Garamond font. It’s a shame, actually, because Garamond is such an elegant font, the last thing I would associate with scientific text. But it’s handy on the drop-down.
Do you know how to resize post font? There is a “Size” option right smack in the middle of
the top row of the formatting icons located over the edit pane. Below is your Garamond passage
in size 4. Does it really not look distinctive enough?
Their dead-heat finish strongly supports the Einsteinian view of space-time, researchers said. The wavelengths of gamma-ray burst photons are so small that they should be able to interact with the even tinier “bubbles” in the quantum theorists’ proposed space-time foam.
If this foam indeed exists, the three photons should have been knocked around a bit during their epic voyage. In such a scenario, the chances of all three reaching the Fermi telescope at virtually the same time are very low, researchers said.
So the new study is a strike against the foam’s existence as currently imagined, though not a death blow.
“If foaminess exists at all, we think it must be at a scale far smaller than the Planck length, indicating that other physics might be involved,” study leader Robert Nemiroff, of Michigan Technological University, said in a statement. (The Planck length is an almost inconceivably short distance, about one trillionth of a trillionth the diameter of a hydrogen atom.)
I would also suggest using a color other than black, except the mods have been known to get
ants in their pants over anything except standard black lettering.
I wasn’t clear in my reply, but if you had glanced again at the passage in question, you would have seen what I meant: the standard (ie w/o another setting change) size of the Garamond letters is smaller. I was referring to the sans-serif font I am using now, where clicking it down gives, for me, a too small letter unless used for footnote or comic effect.
