O/T To Anyone interrested in Physics.

[tkav1980]

im not going to start the same thread here but check this out.

**broken link removed**

 

[terryd5150]

REVENGE OF THE NERDS!!

tkav asks:

ok first question simply put could gravitational pull accelerate you to relativistic speeds?

terryd answers:

Yes, Black Holes are a perfect example of this. tkav, you already know this, though.


Keep this FACT in mind any time you have questions about gravity relative to the speed of light. ALWAYS use this as a constant, as you know it to be true.

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tkav asks:

E=mc^2, so energy can cause a gravitational effect. i think in pictures so let me do it that way for this part. you on a space ship. you shoot a beam of energy out of the front of it to create a gravitational field, since that beam is conatantly moving away from you at C would the distance the spaceship can fall be become infinate because the source of the freld is always moving away from you?

Archaeopteryx answers:

Tommy I've been thinking about your idea of using concentrated energy that is moving at the speed of light to accelerate something to relativistic speeds. It's a super-cool idea, but unfortunately it wouldn't work and here's why. Gravitational force/waves/attraction/whatever you want to call it travels at the speed of light. If the object is traveling away from you at speed c and the gravitational waves are coming toward you at speed -c, then you will measure the gravitational field of the object moving AWAY from you at speed c, so the gravitational field of the energy will never actually reach you. So there would be NO attraction between you and the energy blob.

terryd answers:

Archaeopteryx' answer is probably true to the question, as the question is written.

If your gravitational energy source is moving away from you at C, it would require the effects it has on gravity to RETURN to your position at a speed GREATER than C in order to have anywhere near the desired effect. That won't happen without an additional force accelerating the gravitational energy that is returning to your position.


BUT, if you change the question just a bit and alter the scenario, then C is possible.

What if your gravitational energy WASN'T moving away from your space ship at C?

Think of a gravitational energy source much closer AND fixed to your position, where its effect on gravitational space doesn't have to travel any distance to effect the gravitational space at your position- an energy source that has an immediate effect on the gravitational space at your position.

In that scenario, you DEFINITELY have ability to reach C- depending on the strength of your energy source.

Again, Black Holes are proof of this.


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tkav asks:

just a thought.....could gravitational acceleration be used to break C? the alcubierre metric works by creating a wave and requires negative mass energy. well normal everyday energy can create the front part of that wave where space is being squashed. instead of propelling yourself along a wave like a surfer, why not just slide down the slope like a luge?

Archaeopteryx answers:

Nope. Velocity asymptotically approaches c in gravitational free-fall. Not to mention the fact that the gravitational source must be a finite distance away from the attracted object, so there's always a finite distance it can fall.

terryd answers:

Archaeopteryx is correct with his answer, but I think he is assuming something that you didn't specify in your question. Archaeopteryx seems to be an astute mathematician, he's always going to interpret things a certain way unless you specify otherwise (nothing wrong with being a mathematician, you just have to understand their approach problem-solving).

My point is I think he is assuming a stationary gravitational source, for example a large, unmoving mass like a planet or Black Hole. In that case, he's correct, the distance you can travel would be finite.

I specified earlier an energy source that is FIXED to your position (i.e when it moves you move, vice versa), that is a key condition in my answer.

He also uses the term gravitational free-fall, which would probably be correct in the presence of a negative gravitational force (unless you are talking an astronomically negative gravitional force, perhaps), but the fact still remains that you will have movement, if all other gravitational forces remain constant.

However, by using an opposing gravitational force in the opposite direction at the same time, we no longer have to rely solely on a static gravitational free-fall for our object to approach C, but it now can be accelerated towards C by an opposing gravitational force much more easily due to the reduced gravitational energy in that direction imposed by the negative gravitational force.