Re: anti-gravity? [OT]

On 4/22/2024 12:11 PM, John Larkin wrote:

On Mon, 22 Apr 2024 15:00:21 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote:

jim whitby <news@spockmail.net> wrote:
>

Looking for opinion of persons better educatrd than myself.
>
<https://thedebrief.org/nasa-veterans-propellantless-propulsion-drive-
that-physics-says-shouldnt-work-just-produced-enough-thrust-to-defeat-
earths-gravity/>

>
Has anyone come across the alternative theory of gravity which I first
heard of from P.G.A.H. Voigt?
>
It suggests that the current theory of gravity is rather like the idea
we used to have that there was force 'due to vacuum', rather than air
pressure.  It proposes that the real cause of the gravitational effects
we observe is not an attraction but a pressure.
>
The concept is that a force acts on all bodies equally in all dirctions.
When two bodies with mass approach each other, each shields the other
from some of this force and the remaining forces propel the bodies
towards each other.
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I don't know how it would be possible to test whether this was in fact
how 'gravity' worked and whether it was possible to differentiate it
from the current theory, as the two would appear to have identical
observed effects.
>
>

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Of course little things like the equality of inertial and gravitational
mass (so that objects of different density fall at the same speed) don’t
fit easily into such a picture.
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Also, the rate at which the hypothetical particles collide with matter has
to be extremely large in order to work with very dense matter, such as free
neutrons.
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Neutrons have been observed to follow Newtonian gravity to very high
accuracy in the lab.
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And then there’s the complete absence of Brownian motion in free particles.
With some huge flux of particles carrying the sort of momentum that would
be required to account for the gravitational motion of free neutrons, the
resulting fluctuations would be very visible.
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Besides, if the particles bounce off the gravitating objects, their
velocity distribution will change as a consequence. (Some of them will
rattle around between them, going faster and faster as the objects get
closer.)  Thus there will be a wake effect, like a small plane taking off
right after an A380.  No such effects are observed.
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Not to pile on, or at least not as much as the notion deserves, but if
relativity is completely wrong, then there is only one velocity in a given
reference frame for which the drag force of such a particle ensemble is
zero.
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And, of course, there’s the question of the origin, distribution, and
regulation of the momentum-carrying particles.
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To have any chance of avoiding even these purely classical effects, the
particles would have to have infinite speed, zero mass, perfectly uniform
and isotropic distribution in both position and direction, perfectly timed
arrival at each object to make the fluctuations cancel out, and on an on.
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This is the luminiferous ether, on stilts.
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And then there are matter-wave interferometers, which work not only on
electrons, but on neutrons and even buckyballs.  They set far tighter
limits on most of these classical effects.
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So no, these sorts of theories are not good candidates to explain gravity
or other relativistic effects.
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Cheers
>
Phil Hobbs

 Is there any deeper explanation for conservation of energy, and for
Newton's laws, other than that's just the way things are?
 (That gets philosophical, namely why does mathematics define the
world?)
 

I don't think we know for sure that conservation of energy holds on a cosmological scale, since we don't know for sure the global topology of the Universe.
In a hypothetical Universe that's topologically flat and unbounded there's still the boundary condition at infinity to be considered, which I think could in principle be a singularity sort of like a "white hole", anything could come flying in and conservation of energy can't hold exactly.