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Physics
Topic Started: Tue Jan 29, 2008 1:42 am (176 Views)
Username
Level 9
I don't know what you mean by gravity being a force with no energy. Gravity causes potential energy, but then all the other forces (electromagnetic, strong/weak nuclear) do the same thing. Electricity, for example, is better called the electrical potential. That is, the potential energy a charged object has in an electric field. The reason electrons move through a wire, for example, is because the wire has an electric field that pulls them.

One idea for moving at very high speeds does use gravity. Actually, it's used aleady. Slingshotting around a very massive object uses the objects gravity to accelerate. Satellites and the space shuttle used gravitational slingshotting when coming back from the moon for instance. To get close to the speed of light, you the idea is to slightshot around a very, very heavy, very small object. A black hole. However, you'd still be constrained by the speed of light.

I don't know what you mean by 'your own mass' either haha. Mass is related to energy, energy is related to speed. The faster you go, the greater your mass. Relativity predicts that and object moving at the speed of light would have an infinite mass.
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Geofari
Level 13
Username
Jan 31 2008, 12:47 AM
The faster you go, the greater your mass.

i will have to disagree on that entirely since your mass is a constant
are you sure its your mass that reaches infinity? not your acceleration?
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Username
Level 9
Geofari
Jan 31 2008, 01:20 AM
Username
Jan 31 2008, 12:47 AM
The faster you go, the greater your mass.

i will have to disagree on that entirely since your mass is a constant
are you sure its your mass that reaches infinity? not your acceleration?

No, it's mass. That's what E=mc^2 predicts. That's what Einstien's equations were about. Mass isn't constant at all, it's dependent on your speed. As a side, size also depends on speed. The faster you move, the more you contract. If an object is moving at the speed of light, it has an infinite mass, no length, and does not experience time.

I don't see why your acceleration would increase the faster you go... Acceleration being the change in velocity over time. If that were true, once you started accelerating you could never stop :P
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DeMaGoG
Level 23
So another subject: The Big Bang.

From my understanding this was when all matter in the universe was in one incomprehensibly small point in space and the four forces (gravity, electromagnetic, weak/strong nuclear) were all one force. So my question is what caused the sudden expansion? Was it something internal or did space somehow cause the big bang to occur (like forcing all the matter apart)? Also, scientists believe that right after the big bang, matter was expanding faster than the speed of light (I think due to the four forces). So if one could somehow combine the four forces again could that be used to travel faster than the speed of light?
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Username
Level 9
The neat thing about the big bang is that we have no theory that can describe what conditions were at the time. On one hand, using Einstiens relativity would seem okay, because of the huge mass involved (the universe). But, Einstiens equations can't deal with singularities, and they break down over very small distances.

Very small distances makes one thing 'Hey, then that could be quantum mechanics, that deals with small things'. But quantum mechanics can't handle gravity (as far as I know, 'quantum gravity' hasn't really been defined yet, only discussed) and it's no good for objects of really large masses.

But yea, the four forces were one force, or at least thats a good thing to say since none of the laws we know of that deal with the four forces apply to the big bang situation.

As to what started the big bang, I'm trying to remember the name of the field in one theory, but I can't. It basically said that even in empty space, there are quantum fluctuations of energy. (The metaphor was a frog sitting in a hot bowl. Once it hit the bottom, it would sometimes jump a random distance up, hit the side of the bowl, and slide back down.) At the time of the big bang, these quantum fluctuations could have provided the 'spark' that was necessary to start everything off.

Another, simpler but less specific, idea is to use entropy to explain it (I'm making this up as I go along, thought of it while writing the previous paragraph :P). Entropy is the quantification of disorder, and the universe has a natural tendency to move towards higher entropy, more disorder. For example, when was the last time you saw an egg fly upwards from the table and re-assemble itself after being dropped?

Pre-big bang, the universe would have been in an almost perfectly symettical state. Everything is in once place, all energy would be at a maximum at that spot. Nature wouldn't like it. When it exploded into a mist of energy, nature wouldn't like that either. All across the universe was one uniform blanket of energy. So it started to clump, create matter, ect. Now, we have huge regions of empty space, and small (comparatively) regions of very concentrated matter, a higher entropy.

I don't know if you could combine the four forces to move at the speed of light. Maybe that's what happens at black holes. Supposedly inside a black hole is a singularity, not unlike the one at the big bang, except it has a measurable mass. If you go into a black hole.... who knows what happens?
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DeMaGoG
Level 23
So could dark energy or matter (whichever one has negative mass) be used to weaken a black hole, or even look into the center by repelling the light waves the black hole attracts? Thats the only idea I can formulate that would allow us to actually see the center of a black hole, since light doesn't escape and whatever gets too close becomes a stream of particles. That brings up another question, could a black hole break apart photons (I doubt it but I think I'll ask anyway)?

Also, in diagrams of black holes, they always show a vortex leading to the point of the actual black hole. But if space is 3 dimensional why do diagrams show the force of gravity pulling only in one direction? Shouldn't it be a sphere instead of a vortex?
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Username
Level 9
DeMaGoG
Feb 1 2008, 04:44 PM
So could dark energy or matter (whichever one has negative mass) be used to weaken a black hole, or even look into the center by repelling the light waves the black hole attracts? Thats the only idea I can formulate that would allow us to actually see the center of a black hole, since light doesn't escape and whatever gets too close becomes a stream of particles. That brings up another question, could a black hole break apart photons (I doubt it but I think I'll ask anyway)?

Also, in diagrams of black holes, they always show a vortex leading to the point of the actual black hole. But if space is 3 dimensional why do diagrams show the force of gravity pulling only in one direction? Shouldn't it be a sphere instead of a vortex?

I've never really heard of anyone being serious about dark matter existing, so I don't know if it does. Apparently there is more gravity in our galaxy than the visible mass can account for, so dark matter is the solution. I've never heard of it having a negative mass either :P, because then it would contradict the problem it's trying to solve. But lets assume it does.

I don't think adding anti-mass to a black hole would actually make the singularity visible. In reality, black holes are losing mass all the time. Stephen Hawking figured out that black holes actually radiate energy, decreasing their mass. So eventually, all black holes essentially shrivel up and disappear when they hit 0 mass. I don't think any big explosions happen, but they could.. I don't remember if smaller black holes radiate more energy or vice versa. The reason they radiate energy is because they actually rotate and are electrically charged. Their size, spin and charge combine somehow to make them radiate. The problem is that 1) there are no black holes close enough for us to see this radiation and 2) the information coming out of them wouldn't be useful as to what happens to things going into them. Which makes me think of Information Theory, which also predicts that black holes have to radiate energy, but thats not important.

So I think if you added anti-matter, it would just speed up this process, thereby shrinking it faster. It wouldn't let us know what happens on the inside. Now if anti-matter had a reverse gravitational effect, I guess what we could do is create a 'white hole'. A white hole would do the exact same thing as a black hole, but instead, it would repel all light with a very high anti-gravitational effect. If we put a white hole inside a black hole.. I don't know what would happen haha. It's important to know though, that we wouldn't know anything about what a white hole looks like either. Because by its definition, light would never reach it. So again, we would have no information about what happens to the white hole.

As to photons getting ripped apart, they don't, but other particles do. It was actually an alternative solution to Hawking's theory that black holes radiate. In quantum mechanics, there are such things as virtual particles. These special particles only exist in pairs. They spring out of empty space as a quantum fluctuation, joined together, separate, then collide in a burst of energy and disappear. Very short lived, these virtual particles. The idea was that if these virtual particles appear in space everywhere, what if they appeared at the edge (event horizion) of a black hole? They would appear, separate, one would get sucked in, and the other would continue on into empty space. We would see that as energy apparently coming from the black hole, when really it was never inside.

Black holes are spheres. On paper, its hard to show what exactly a black hole would look like. In reality, it wouldn't look like anything. It would just be dark. There is no substance to a black hole. It's just the gravitational field caused by a singularity. Where the idea of a vortex and a sphere comes in is whats called the 'event horizon'. The event horizon is the point where, after that, nothing can escape. So you could, in theory, orbit a black hole JUST above the event horizon, and still escape. But as soon as you dip below it, nothing can get you back. So what pictures often show as the black hole is really the event horizon.

One idea that is deeply debated that could allow for faster than light speed/time travel is whats called a naked singularity. That is, a singularity that is not concealed by a black hole. No one knows if they exist or not, but if they do, there is an opportunity to experiment with physical properties that couldn't exist anywhere else. Another idea is a ring singularity. That's a singularity with a hole in the middle, shaped as a ring or donut. These could exist as naked singularities, or inside black holes. If they do exist inside black holes, then it would be possible to enter the event horizon, and pass through the middle of the singularity without getting destroyed, emerging on the other side. At that point, no one knows what would happen. People suggest alternate universes ect. but I've never really heard of WHY they suggest it. I think you would just get stuck in the middle of it, as you would have an equally infinite gravitational field pulling you in every direction.
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Etra
Level 22
Split the physics related stuff from "GOD/JESUS/SATAN."
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DeMaGoG
Level 23
That last point reminded me of something... Lets say a tunnel was dug straight through the center of the earth (one side to the other). Ignoring any likely temperature changes, what would happen to a person if they jumped into the hole? Once they passed the center of the earth would they begin to slow down? And since the outside of earth travels faster than the inside, would it be possible to avoid hitting the walls, even if the hole is a mile in diameter (in other words, since you are spinning with the earth at the speed the crust is spinning with the earth at, as you fall you would still "spin" at that speed while the closer to the center of the earth you get, the slower the earth would seem to spin)?

This brings up something else. Let's say we can make a rotating pole in space that can be as long as we want it to be and spin fully and not be obstructed. Now lets say we want it to spin 60 times per minute. How long would the pole have to be before the end would be traveling 300,000,000 meters per second? If you want to change the amount of rotations per minute, feel free.
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Sarge
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Hacker Hunter
About the hole dug through the earth..

When you get to the direct center, I think you would be suspended in mid-air, since gravity pulls to the center of the object.
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Username
Level 9
Lets break the first problem into two seperate things. Firstly, if you imagine the earth as a perfect sphere, and say that its stationary in space, what would happen if you jumped into a hole directly through the middle? The short of it is that you would eventually get to the center of gravity and stop (like Sarge said). As you fell toward the centre, you would accelerate, you would get to the centre and, because you already had a velocity, fly past it. Then you would decelerate and eventually begin to fall back again toward the centre. This would repeat until you ran out of velocity and just stayed at the centre. I think though, that you would get crushed by the gravity before you had a chance to really settle :P.

Now, if the Earth was spinning (but stationary in space) we have to look at two things, a spinning ball and something stuck to it. The thing stuck to it, you, have whats called a rotational velocity equal to the rotational velocity of the surface of the ball (duh :P). Since we're looking at both objects seperately, you should maintain that velocity unless something forces it to change. Now at the centre of the ball, the rotational velocity is 0. A point at the centre doesn't move at all. If nothing was slowing you rotational velocity, it would remain constant as you fell toward the centre: you'd hit the side. There might be a dampening effect because of the air, but you'd be moving very quickly, so I don't think it would be enough to stop you from hitting.

The motion of a rotating pole is very easy to model, you can just use the relationship v=rw where v is the tangential velocity (the velocity of a particle at the end of the pole in the direction perpendicular to the pole), r is the radius, and w is the rotational velocity. Using your numbers,

300 000 m/s = r(60rpm)
(300 000m/s) / (60rpm) = r
(300 000m/s) / (6.28 rad / s) = r
47 770m = r

That's a pretty short pole, in terms of space at least. I think I see where you're going with this, its been brought up before, but not with a pole, but with a galaxy or even the entire universe. If the galaxy is rotating, which it is, then the stars on the edge must be travelling at near (or greater than) light speed.

The explanation of why that doesn't happen to me seems a little bit sketchy. The only source I've seen really discuss it is Stephen Hawking in 'The Universe in a Nutshell' (which is a really good and easy to understand book by the way). He explains it using the idea of sum over histories. Basically, theres a principle which states (this is a quantum concept) that any particle will take every possible path to get from point A to point B, with whatever energy it has. So an electron shot from an emitter will travel every possible way to get to where it is detected. (This is also part of the parallel universe idea, each path is in a different universe). When you increase your speed, you also increase the amount of energy required to move at that speed. Also, that means that there are less possible paths to take to get to the same location (less energy to spend going in circles before you get there, more is required to actually make the trip). As you approach light speed, you need ALL of your energy to take the ONE path that will get you there. That means that for a slow moving object, there are more possibilities than for a fast moving object. The way that is interpreted is that there is a very, very low probability of an object moving at or close to the speed of light.

It sounds like dodging the question by saying 'Well, statistically its not likely'.
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FaZ-
Level 39
Faster than light communication has been solved. =D
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