[jamest (OP)]

Christopher wants to know what physics has to say about how fast things can possible travel...

[paul cotter]

A mass that is moving at a speed v undergoes an increase in mass to the factor of 1/√1−vsq/csq where c=speed of light in vacuo.  At speeds commonly encountered this factor is close to unity and no increase in mass is detectable. When the mass increases it's speed to a significant fraction of c the increase in mass becomes noticeable and thus requires more energy to accelerate further. As the speed of light is approached the mass and the energy necessary for further acceleration increase without bounds and to reach the speed of light the mass would become infinite with infinite energy necessary to get there. This is obviously impossible. Thus the speed of light can be approached asymptotically but never reached. There are speculated particles called tachyons that travel faster than light and can approach the speed of light at high energies asymptotically from "the other side", ie always above the speed of light.

[evan_au]

As Paul says, you can't accelerate an object to the speed of light (or beyond) using a finite amount of energy.

With Dark Energy, it is spacetime itself which is expanding. There is no known limit to how fast space-time can expand.
- So some distant objects which are visible to us today (relative speed < speed of light) will one GigaYear not be visible to us (relative speed > speed of light), and no photons will reach us from those objects.

[Janus]

While the infinite energy argument is one way to explain it, it itself is a result of something more fundamental.
Relativity is really about the nature of time and space and their interrelationship.
It turns out that c is very instrumental  to this relationship.
Let's look at an example:
Ship A is accelerated up to 0.99c relative to its starting point.
Ship B is accelerated up to 0.99c relative to the same starting point, but in the opposite direction.
How fast are A and B moving relative to each other?
Prior to the advent of Relativity as a theory, we would have said both A and B would measure that they are moving 1.98c relative to each other.
Post Relativity gives us something else. We get an answer of 0.99979596...c for the speed either would say that the other was moving relative to themselves.
One issue the infinite energy answer has is that, unless you dig deeper into the theory. it can leave the reader with the idea that there is some absolute state of rest or reference for the universe that you can't move greater than c relative to.
This is not the case.
Let's change the above scenario a bit. Ship A, still travels off at 0.99c from the starting point.  But now it fires a projectile forward.  Nothing prevents him from firing that projectile at a speed of 0.99c relative to himself as he measures its speed.
However, someone back at the starting point will measure that projectile as moving at 0.99979596...c relative to himself, and Ship B would measure it to have a speed of 0.999998975...c
That projectile could fire a second projectile ahead of it at .99c, and everyone else would measure it as moving less than c.
It really doesn't matter whether you consider A, B, projectile 1, or projectile 2 as being "At rest", it's all the same.

[Zer0]

@Christopher

Faster Than Light(FTL) phenomenon is a Realistic Possibility.


@jamest

Hello there and Welcome to TNS!

ps - : )