Not quite.
DA is actually thought of as an underlying expansion of space-time not antigravity.
That’s an internal contradiction: in general relativity, a positive spacetime curvature *is* gravity, and a negative spacetime curvature (which is what we observe with dark energy) *is* antigravity.
Granted, most cosmologists shudder at the prospect of using the word “antigravity,” since the disinformation campaign against ufology has been so amazingly successful that even the word is toxic to academic careers. But as the old saying goes, “if it walks like a duck, and quacks like a duck – it’s a duck.” Dark energy appears to be an antigravitational effect, and this is perfectly acceptable within the framework of general relativity.
(Note: why are you abbreviating “dark energy” as “DA?” I’ve seen the abbreviation “DE,” but never “DA” – is there some reason for this?)
In other words, the same effect that makes empty space non-zero energetically is likely the source for DA. What this means is that DA is not antigravity -- it is the stretching of space-time in empty space.
Again: gravity and antigravity are both curvatures (or “stretching,” if you prefer) of spacetime. You’re making a distinction where there is no difference.
Sean Carroll offers the best succinct explanation of our best model of dark energy – which still remains the best fit with astronomical observations, here:
Why Does Dark Energy Make the Universe Accelerate?
(Note: I don’t agree that the first Friedmann equation is superior to the second for explaining dark energy, because the second Friedmann equation has greater physical/causual explanatory power, but it’s still a wonderful and accurate article)
Case in point: Stars don't stretch out like empty space does. Galaxies don't. The space between them does.
If the cosmological constant model of dark energy is right, then this is incorrect: spacetime expands at all levels, including the spacetime between atoms (and even quarks) but the effect is simply negligible at those scales, even over ordinary cosmological timescales. That’s the basis of the “Big Rip” model of cosmic evolution that was inspired by the discovery of dark energy – eventually even celestial objects and atoms themselves may be ripped apart by dark energy:
Big Rip - Wikipedia
And presuming you can figure out what DA is doesn't mean that it will necessarily be useful at all. Because if you can make it do what it does, you can stretch space behind you but you can't collapse it in front of you.
That’s the easy part, comparatively speaking: all you need is an ordinary gravitational field in front of you.
Think of it this way: all you need is a gravitational gradient, with a positive (attractive) gravitational field in front of your craft, and a negative (antigravity) field behind your craft. So in the middle, between the two, the spacetime is sloped, rather than flat. The center of mass of your craft then naturally “falls” forward in a state of free-fall, accelerating as long as the field is maintained. Note that once the field is created, the only energy required to continue accelerating is whatever losses exist within the system (via resistance, or hysteresis losses, or what have you). This is totally unlike the rocket principle, where every gain in acceleration requires a significant expenditure of energy.
IM is not conceptually equivalent to GM.
If you’re saying that “inertial mass is not equivalent to gravitational mass,” then you’re not talking about academic physics (which is fine; I always enjoy hearing about alternative physics theories). In mainstream physics the equivalence of inertial and gravitational mass is a pillar of the general theory of relativity called “the weak equivalence principle,” and it’s been proven to hold with every experiment performed to test it to within 1 part in 10^12:
Equivalence principle - Wikipedia
First of all, the drop in IM referenced with the concordant drop in GM in your example is not due to AG. It's due to the photon radiating energy, which results in a drop in M-A for the object, which results in a drop in GM.
I never said that binding energy was due to antigravity – in fact, I already explained that the drop in mass via nuclear/chemical/gravitational bonding is exactly balanced by the loss of mass-energy in the radiated photons.
I was simply pointing out that there are several known methods by which inertial mass (and yes, therefore gravitational mass) can be reduced via binding energy – so in practice mass is not necessarily a constant, but can become a variable. That has interesting implications.
Oh, in my post above, I forgot one of my points:
If you could somehow use dark energy to expand the space under your craft so it was falling at the same rate it was expanding the space below it, maybe it would hover from the reference point of the ground.
Yep. You’re talking about establishing an inverse gravitational field (aka an “antigravity” field) between your craft and some gravitating body like a planet. In which case both the craft and the gravitating body would be repelled by that field (which would have an insignificant effect upon a celestial body, but could suspend your craft above the surface, or even accelerate your craft away from it).
But would it not also distort the view under the ground - i.e. the light cone from the craft would become infinitely long as the space it passed through stretched out?
Not infinitely. Assuming that we’re talking about a craft suspended above the Earth, the inverse gravitational field would be exactly the same in magnitude as the acceleration field of the Earth so the effect on spacetime would be very small, and simply negate the existing and minuscule spatial compression exhibited by the Earth's gravitational field. There would also be a subtle inverse gravitational lens effect, and the negative gravitational field repelling the craft would probably be detectable using an experiment like the Pound-Rebke experiment, which would demonstrate the gravitational *blueshift* of the antigravitational field (the two forms of gravitational field would cancel out to some extent, reducing the ordinary gravitational redshift in that region):
Pound–Rebka experiment - Wikipedia
Would it not also stretch the space in the molecules of the air and ground until they break (which should release energy) or even break open the atoms (causing a nuclear reaction emitting radiation)?
In a weak field case like a craft suspended over the Earth, a negative gravitational field would reduce the pressure of the atmosphere in that region, but it would take an extremely steep gravitational gradient to break up molecules or atoms. But even if you could create a gravitational field gradient intense enough to dissociate matter or nuclei – they wouldn’t radiate energy when they broke up. Matter radiates energy when it becomes *more tightly* energetically bound, and *absorbs* energy when it becomes less bound, because binding energy is always negative.
But here’s an interesting aspect: an antigravity field is a region of increased rate of time, which creates a blue shift. So if you place an object in thermal equilibrium with the environment within such a field, the ordinary infrared photons that it emits would have shorter wavelengths. In a strong enough field, infrared photons would become visible light frequencies. So ordinary room temperature atmosphere would glow.
Sounds kinda familiar, huh?
