On 12 May 2020 at 13:02, Christopher Sean Hilton wrote:

> I took the "Do ships have landing struts" discussion to a friend who's
> a Physics professor at the University of Buffalo. He understands
> General Relativity and Quantum mechanics where I don't go much past
> Newtonian physics and Special Relativity. There were a few relevant
> themes in our conversation:
>
> * According to current physics, anti-gravity is impossible so this
>   entire conversation is really moot;

A number of physicists disagree, Dr Robert forward discusses several
ways to do it in one of the chapters of his book "Indistinguishable
From Magic".

The "simplest" way is to place a large *dense* mass above you. This
isn't *too* far* above current tech. But not terrible useful for a
vehicle :-)

Other ways involve accelerating high density materials around
toroidal "coils".

And, of course, there are arguments about whether matter with
negative mass could exist. Nothing in theory says it can't, but it
would have a lot of weird properties.

You don't necessarily *need* "antigravity" anyway. "contragrav" could
be something that interacts with or modifies the structiure of
spacetime.

Using the "rubber sheet" model of a gravity well, "interacting" would
be equivalent to grabbing hold of the "sheet" either to maintain
altitude, or to climb up or down the slope. That's the most likely
model for CG.

"Modifying" would be changing the slope around the CG device. That'd
be like making a "step" in the slope. That would be how grav plates
work.

So for CG, it'd take a certain amount of power to run the device.
climbing would require *at least* the change in potential energy if
not more. Descending would be dumping enegy into the unit, which
would have to be gotten rid of (feed it to batteries, or radsiate it
away as heat).

So hovering would only take the base enerfgy to run the CG.

Do note that not having the means to get rid of excess energy when
descending is *bad*. There were some buses built 40 or 50 years back
that tried using regernerative braking (using the wheels as
generators to slow down). Since they *weren't* electric, they ran the
generated electricity thru a big cast-iron radiator grid under the
bus.

The design was scrapped after a few incidents of the grid *melting*
on long or steep downslopes. They had to dig the molten iron out of
the street and the bus out of whatever it ran into at the bottom of
the hill.

Grav plates are even more fun. The strengtyh of gravity depens on the
slope of the "sheet", not how far up or down the slope you are.

That means that if you can affect the slope, it doesan't need the
energy equivalent of a planet to get 1g in space of fighting same to
get zero g on the ground.

The kicker is that the slope is *continuous*. So if you tilt an
area,you are going to create steeper areas "above" and "below" it
(remember this is a 3d model of a 4d effect).

Worst case is if you tilt things so that you have a vertical slope at
the upper and lower edges and a flat spot in between (zero gee).
That's essentially "infinite" gravity at the upper and lower edges.

So if you head towards the "upper edge" you'll stop dead and cannot
proceed any further. Not unless you can supply the potential energuy
difference in one lump.

Anybody "above" you that approaches the edge is gonna get "thrown"
into the zero g area with all of the potential energy difference
turning into kinetic energy. Ouch.

And if you approach the "lower" edge, the same thing happens to you.

If you lessen the slopes of the transition areas, it gets easier to
cross them, but that also takes up a larger area for the transition.

And if you don't lower (or raise) the slope in the area (volume) with
artificial gravity as much that too helps with the transitions. Note
that that slope inside the volume is the strength of the grav field.
Flat is zero-gee, and vertical would be infinite gravity.

Another nice thing about this for ships, is the grav plates aren't
affecting anything outside the ship. Which avoids all *sorts* of
problems.

Just watch out for the transition zones near the plates.

Oh yeah, this also means you need a sort of "grav lock" to easily
(and *safely*) transtion between areas with different gravity on the
ship or to exit the ship in space.

For staterooms and the like, just dial it up or down to match the
corridoor to enter or leave. For entering or leaving the ship, dial
the grav in the airlock up or down.

Oh yeah, this means that lifting things inside an area with
artificial gravity feeds energy into the plates, and lowering or
dropping things pulls energy from them. Got balance the potential
energy changes.

Using this model the areas above and below a deck (or stack of decks)

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com