Taking Warp Drive Seriously:

[StringJunky]

5 minutes ago, Mordred said:

Then you add the positive pressure region on the sail. The momentum is due to the pressure differential on one side of the sail compared to the other.

 

Your correct though on the above. 

Cheers Mordred.

[Strange]

6 hours ago, StringJunky said:

I thought momentum from the fan pushing the boat backwards would be cancelled by the momentum imparted on the sail from the airflow going the other  way. leading to no net motion.

It is. But a sail isn’t just a surface that is pushed by the air hitting it. It acts as an airfoil and generates “lift” as well. 

[StringJunky]

2 hours ago, Strange said:

It is. But a sail isn’t just a surface that is pushed by the air hitting it. It acts as an airfoil and generates “lift” as well. 

OK.

[Markus Hanke]

17 hours ago, GaryV said:

For example, I never claimed this would allow FTL travel.

This entire thread is about FTL travel through “warping” spacetime (see OP), so it is reasonable for people to assume that is what you meant.

17 hours ago, GaryV said:

If warping space (I.E. causing a gravitational field) with only energy were possible

Of course it is possible. Any form of energy-momentum has a gravitational effect - that can be mass, but also less tangible forms of energy-momentum such as electromagnetic fields. You could, for example, alter the geometry of spacetime by generating very strong electromagnetic field (e.g. lasers) in a small region. To give a real-world example, the magnetic fields around magnetars are so strong that they make a non-negligible contribution to the overall gravity of these objects.

17 hours ago, GaryV said:

The reason most people don't want to seriously take on this topic is the need for exotic matter.

You don’t need exotic matter to generate gravity. You would only need it in order to set up some very specific geometric configurations, such as a naked Einstein-Rosen-Bridge that is both stable and traversable. For your example with the space station, any form of energy-momentum would work - but you would need a lot of it to have any kind of appreciable effect, which is where the problem lies. It isn’t really feasible from an engineering and resources point of view.