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Next obvious question: are you sure the quantum fluctuations really have energy, or is it possible they don’t, thereby eliminating the cosmological constant problem? Answer: Yes, I’m sure quantum fluctuations do have energy; it’s what’s called zero-point energy, and it’s completely fundamental to quantum mechanics, and due yet again to the uncertainty principle. And this can be checked: n a clever experiment, the energy in a small region can be made to have a measurable impact called the “Casimir effect”, which was predicted in the 1940s, first observed in the 1970s and tested more carefully in the 1990s. [There is some controversy about whether this is really relevant to the question, however.]
They are on the other side of the controversy, challenging the claim about the Casimir effect and while they claim that QFT has some problems even they don't seem ready to "throw it out" but think it needs to be fixed:
Let us come back to physics and to the simplest reading of the vacuum energy. ...
Does this large energy exist for real? That is, does it have observable effects? In particular: does it act as a source for the gravitational field, as all forms of energy are known to do? Does it have a gravitational mass (and therefore an inertial mass)?
An effect commonly put forward to support the “reality” of such a vacuum energy is the Casimir effect. But the Casimir effect does not reveal the existence of a vacuum energy: it reveals the effect of a “change” in vacuum energy, and it says nothing about where the zero point value of this energy is. In fact, simple physical arguments indicate that the vacuum energy, by itself, cannot be “real” in the sense of gravitating: if it did, any empty box containing a quantum field would have a huge mass, and we could not move it with a force, since gravitational mass is also inertial mass.
Then they suggest some different ways of looking at QFT. They conclude:
A shift in vacuum energy does gravitate....
Why standard QFT has so much trouble adjusting to this straightforward physical fact? We do not know the answer...
...we do not yet fully understand interacting quantum field theory, its renormalization and its interaction with gravity when spacetime is not Minkowski (that is, in our real universe). But these QFT difficulties have little bearing on the existence of a non vanishing cosmological constant in low-energy physics, because it is a mistake to identify the cosmological constant with the vacuum energy density.
This single postulate leads us to the correct, observed numerical value of the cosmological constant!
I'm sure I'm not telling you anything you don't already know, but in addition to throwing out QFT, throwing other modern foundations of physics like relativity and the standard model to replace them with your models which he probably never heard of before won't be an easy sell.
You can’t know a field’s value, and how it’s changing, at exactly the same time; your knowledge of at least one, and typically both, must inevitably be imperfect.
Another example: the response of an electron to a magnetic field can be measured to about one part in a trillion;
That means the energy density of quantum fluctuations of the electric field is roughly a million million million times more than ordinary matter, and so the mass-energy in fluctuations of the electric field inside a cube one meter on a side is about a million million million times larger than the mass-energy stored in a cube of solid brick, one meter on each side. How much energy is that? Easily enough to blow up a planet, or even a star!
These statements must really seem bizarre to you. They are bizarre, but hey — quantum physics is bizarre in many ways. Moreover, neither quantum mechanics in general, nor quantum field theory in particular, have previously led us astray.
In gravitational physics there is nothing mysterious in the cosmological constant. At least nothing more mysterious than the Maxwell equations, the Yang-Mills equations, the Dirac equation, or the Standard Model equations. These equations contain constants whose values we are not able to compute from first principles. The cosmological constant is in no sense more of a “mystery” than any other among the numerous constants in our fundamental theories.
A given QFT with a finite cut-off M can be interpreted as an effective theory, valid at energy scales well below M, obtained from a more complete, high-energy theory, by integrating away the high-energy modes.
We think that the origin of the confusion is that there are two distinct ways of viewing the cosmological term in the action. The first is to assume that this term is nothing else than the effect of the quantum fluctuations of the vacuum. Namely that lamda = 0 in (21) and the observed acceleration is entirely due to the radiative corrections lamda (in the above notation). The second view is that there is a term lamda in the bare gravitational lagrangian, which might (or might not) be renormalized by radiative corrections. The two points of view are physically different. We think that the common emphasis on the first point of view is wrong.
In other words, it is a mistake to identify the cosmological constant lamda with the zero point energy lamda of a QFT, for the same reason one should not a priori identify the charge of the electron with its radiative corrections.
the spacetime sourced by the vacuum oscillates alternatively between expansion and contraction, and the phases of the oscillations at neighboring points are different. In this manner of vacuum gravitation, although the gravitational effect produced by the vacuum energy is still huge at sufficiently small scales (Planck scale), its effect at macroscopic scales is largely canceled. Moreover, due to the weak parametric resonance of those oscillations, the expansion outweighs contraction a little bit during each oscillation.
We obtain lamda*L_P^2 = C*beta^2*exp(-24pi*2*mu), where C depends on n_gamma/n_m, the ratio between the number densities of photons and matter. This leads to the correct observed value of the cosmological constant for a GUTs scale inflation and the range of C permitted by cosmological observations.
inflation may “self-terminate” naturally by its own action of stretching wavelengths to enormous sizes.
I also agree with a debunking of the "coincidence argument" in section III, i.e., that it is just too small of a probability that things are the way they are.
We can have a very well defined momentum and a very ill defined spatial spread, but we will always have at least some uncertainty in the momentum too.
The Casimir effect is sometimes cited as "proof" of vacuum energy, however even those who make such a claim have admitted it's controversial:
And once we admit the possibility that Lorentz (or my alternative) may be correct, we then of course are returned to the idea of a luminiferous aether.