Sooner or later we (and by "we" I mean humanity, rather than Sturton, the intercalary and myself) will develop decently powerful space propulsion systems, capable of accelerating a spaceship up to a large fraction (say 0.99999...) of C. This is good, because at 0.99999...C, you can get anywhere in the
universe in about 5 minutes, thanks to time dilation.

But wait - Houston, we have a problem! If we accelerate our spaceship at 1G, it will take about 1 year to reach 0.99999...C. For most of that year, the crew will not experience significant time dilation, and hence they will experience most of that full year of acceleration. This is a drag.

The solution, of course, is to accelerate at more than 1G, and ideally at about 1000G. This will reduce the acceleration period to something like 8 hours (mostly experienced) - enough time to watch a movie, have an in-flight meal, and catch a little sleep. To give a 1000G acceleration, all we need is a bigger engine. So that's OK.

But wait - obviously a major malfunction! With an acceleration of 1000G, our intrepid crew will be reduced to a thin, multi-layered paste on the back wall of the spacecraft. Even if we fill the spaceship with water to cushion the force, 1000G will still be enough to fractionate your bones from your fat. Not at all good.

This, then, is the coupling problem - how to transmit a force equally to all components of the body, so that it can be accelerated very intensely without dying.

So, here's what we do. First we build the spaceship with its super-duper engine, and we build it strong enough to survive 1000G of acceleration. Fine.

Now, in the nose of the ship, we put a large mass. A quite very much large mass. For compactness, and to leave room for the in-flight catering supplies, we will use a black hole of perhaps a few trillion tons. Of course, it's notoriously hard to fix a black hole in place (duct tape is hopeless, for instance), so we'll use a charged black hole and hold it in place with a big electric field.

So, we have a big big mass at the nose of the ship. The ship, by the way, is quite long (maybe a few hundred kilometres). By dint of careful calculation and use of the right mass of black hole, there will be a space further down the ship at which (a) the black hole is exerting 1000G of upward pull and (b) the G-gradient is only about 1G per metre, so tidal forces aren't too bad.

Now we're all set. We put the crew in the spaceship, initially at the very bottom (quite far from the black hole), and then we fire up the engines. The ship starts to accelerate upward at, initially, a few G. The crew, meanwhile, take an elevator that brings them closer to the top of the ship, and hence closer to the black hole.

At some point, the crew will be close enough to the black hole that its upward gravitational pull exactly matches the acceleration of the ship as a whole, and the crew feels themselves weightless. We then open the throttle and ramp up the acceleration to 10G, 100G....1000G, and during this time the elevator is rising and bringing the crew closer to the black hole in the nose.

Once we reach 1000G acceleration (of the ship), the elevator stops at the point where the black hole is providing 1000G of upward pull on the crew. (The actual pull will be slightly greater at their head, and slightly less at their feet. For this reason, they would find it convenient to stand upside down, feet facing the black hole.)

And - gadulka! - the spaceship can now accelerate at 1000G, with the delicate, squishy crew members coupled to it gravitationally and able to enjoy their in-flight drinks service in the usual way.

Can the tidal force be used to provide artificial gravity for the passengers?

I'm imagining a passenger module divided into three pieces:

An aforeships compartment, closer to the hole, where people stand with their feet towards the hole, experiencing 1001g of gravitational acceleration counterbalanced by 1g of locally upwards mechanical force from the floor;

A behindships compartment, further from the hole, where people stand the other way up, feeling 999g of gravitational acceleration supplemented by 1g of locally upwards pressure from the floor;

An inthemiddleships compartment, locally weightless, where the passenger module is attached to the main spine of the ship.

The two "locally upwards" forces point in opposite directions, placing the module as a whole under tension, but cancelling each other overall.

//Can the tidal force be used to provide artificial gravity for the passengers? // Well, yes.

At any point along the ship, the experienced G-force will be:

N=A - gM/d^2 (or something like that), where N is the net experienced G-force, A is the actual acceleration of the ship in space, g is the gravitational constant (should be capital G, I think, actually) and d is the distance from the black hole.

So, at some point along the ship, for any given set of circumstances, N will go from being positive (toward the bottom of the ship, i.e. pulling you to the floor of the rocket) to negative, and obviously zero somewhere in between.

Assuming that you want something like 1G acting on your centre of mass, you could have two "floors", one nearer and one further from the top of the rocket. People would walk around upside-down on the upper floor, and right way up on the lower floor. So, in effect it would be a room where you could walk on the floor or ceiling, but be weightless mid-way between the two.

// enough to fractionate your bones from your fat. Not at all good //

... unless you want to make healthier kebabs ?

Ohh .. Kay ...

Are you listening ? Are you ? THAT MEANS YOU, PRODBURY ... Now, open your text books atSTOP THAT BLUDGEWICK, IT'S DISGUSTINGLY UNHYGIENIC, DON'T YOU HAVE A HANDKERCHIEF ? chapter six ... right ...

Now, pay attention. YOU DON'T DO IT LIKE THAT. Newtonian reaction drives are fine for minor changes of orientation, but if you want to cross interstellar distances in reasonable timescales, something a trifle more sophisticated is obligatory.

Yes, [8th], we assumed that you would like to make some oblique reference to a hypothetical poorly-defined alternative to reaction drives. If you would care to give a little more detail, obviously, we will be happy to take it under consideration.

IAmNotAScientist, [2 fries], but Wikipedia tells me that the unit of
measure for that Gravitational Constant includes an inverse kilo
(always useful to pack in your checked luggage); so, there's
probably a "mass" term in the vulgar fraction on the right hand
side of that equation, measured in right-way-up kilos, to cancel it
out, so that the whole thing can then be subtracted from
acceleration without semantic embarrassment

Using a similar approach, we can solve intergalactic travel
by simply directing a black hole that affects the position of
the sun to take the entire show on the road

That would be an excellent idea. The problem with very fast space travel is that, although you may be back in time for tea, it's likely that tea itself will have evolved in the meantime. Taking the whole planet along with you would solve that problem.

Here's another idea: don't travel at all but
instead recreate your destination where you are
now. It doesn't matter how accurate your recreation
is because you can never be confident what your
destination looks like, so any recreation of it is
as good as any other. The reason for this is that,
because information can not be transmitted faster
than light, any information you may think you have
about your destination will always be out-of-date;
You can never be sure what your destination looks
like now or will look like when you arrive. Any
opinion as to what your destination looks like is
equally valid.

Why does the propulsion unit have to accelerate at the
same speed as the hab module? Couldn't we simply fasten
the habitat module onto a very long, very stretchy bungee
cord or stick of chewing gum?

<Somewhere out in space> Huge explosive acceleration
takes place, accelerating the end of a stretchycord in the
direction of Planet NewEarth where ever it happens to be.
At the other end of the stretchycord, a huge hab module is
accelerating at a rate that is a ratio of its inertia to the
faster moving end, eventually getting up to an appreciable
speed.

//eventually getting up to an appreciable speed.//

Yes, but 'eventually' is quite a long time.

We want to accelerate people at 1000G, so they can get up to near-light-speed quickly. The only way to do that, survivably, is to apply a force to each atom in the person, proportional to that atom's mass. Gravity is, as far as I know, the only way to do this.

Re. [8th]'s link - it seems that the only place Alcubierre could find
the right kind of negative density was in a Casimir vacuum. Now,
there's plenty of vacuum in interstellar space, but a Casimir
vacuum has to be very, very flat. So, if you first reduced your crew
to minimal lamina by unbalanced acceleration, then you could fit
them into the sub-micron-thick vacuum in which Casimir forces
would enable the Alcubierre drive required to protect them from
unbalanced acceleration. Job done.

This asks the question, how sharp a gravity gradient would be needed to separate quarks. The energy to separate quarks should be equatable to a gravitation force differential over such a minuscule distance.

I was reading this post, nodding approvingly as
there were no apparent flaws, until I got to the
part which said “duct tape is hopeless” whereupon
I knew it was all bollocks and stopped reading.

You forgot about the time-dilation effects of the black hole
itself. I can't remember how it all goes (G and M's and
square-roots and such...) but it will definitely make a
difference to the time-span of such an endeavour.
Of course, capturing a black hole in the first place, with-out
it capturing you, is the tricky bit...

// time-dilation effects of the black hole itself// Quiet, for
cod's sake. We told all the first-class passengers that the trip
would only take three hours. We expressly _didn't_ mention
how long three hours would take.