Theory of Relativity

I'll have to look at some quantum physics text to see if makes sense that those leptons and quarks are as small as one can get. I wonder if "particle" is even a good metaphor to use to describe them. With the detection of the Higgs boson recently, that theory is probably on firm ground, but I don't know much about it.

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Originally Posted by mal4mac

I think the problem with this argument begins before the "completion of an infinite process" problem.

Doesn't mathematics only make sense in "our world"? And in our world you can't just keep chopping things in half. How would you chop a Higgs boson in half?

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I think you are right about the problem. There is a difference between the process of getting closer and closer to an infinite collection of something and actually finishing that process and having the infinite collection to work with.

If one assumes one can actually have infinite sets of things then one can use logic to see what consequences follow even if in the real world infinite sets of things don't exist.

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Originally Posted by cacian

Thank YesNo for explaining this most helpful and I am now beginning to have a feel for it.
If I may add then, this simply platonic reasoning because using a microwave or playing tennis in a different planet/ galaxy is not going to happen.
Unless of course one wishes to make a film out of it to demonstrate what one means.

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We won't be able to reach that galaxy to test out whether we would need to do anything special or not to play tennis or use a microwave oven. However, from the point of view of anyone on that galaxy moving away from us, we are in that situation right now. They think we're moving away from them at a fast speed.

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Originally Posted by YesNo

I'll have to look at some quantum physics text to see if makes sense that those leptons and quarks are as small as one can get. I wonder if "particle" is even a good metaphor to use to describe them. With the detection of the Higgs boson recently, that theory is probably on firm ground, but I don't know much about it.

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In theory you can go as small as you like, in fact, particles are usually considered to be point particles in quantum physics texts - that is, infinitely small, but the uncertainty principle would make them look like fuzzy balls, if we could see them, which we can't.

The smallest things we can see (or, actually, feel!) are atoms:

http://www.nanooze.org/english/artic...icroscope.html

(That nanooze site looks a good one for kids into science...)

I admire you lot for such great patience towards particles atoms and whatnot.
I totally follow that chain of thought no matter how hard I would like to.
The point of quantum is that it does not matter where you are can still see it but cannot quiet define if one was not aware of it.
I mean humans must be quantums themselves if we were observed by partilcles or atoms.
In other words if atoms had eyes they would describe a human going about his or her bunsiness as a quantums of an earthal dimension. Juts a reversed psychology there for a minute haha.

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Originally Posted by mal4mac

In theory you can go as small as you like, in fact, particles are usually considered to be point particles in quantum physics texts - that is, infinitely small, but the uncertainty principle would make them look like fuzzy balls, if we could see them, which we can't.

The smallest things we can see (or, actually, feel!) are atoms:

http://www.nanooze.org/english/artic...icroscope.html

(That nanooze site looks a good one for kids into science...)

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I didn't realize that there were "atomic force microscopes" which sound pretty interesting nor that an electron microscope would not be able to see colors, which makes sense now that I think about it.

On a theoretical level the spacetime grid seems like it should be flat and allow one to go out to infinity in both the space and time dimensions since nothing logically stops us from doing do. Also we should be able to break up any world line into points that correspond to the rational numbers and the irrational numbers. Those sets of points would be disjoint and both would be infinite sets although they would be different sized infinities. So there is logically smoothness and infinity all over the place.

However, once one starts looking at the spacetime grid as populated with matter and energy upon which one can perform experiments, one finds that the universe has to be finite or we couldn't survive in it and general relativity turns up the possibility of black holes representing singularities in the spacetime grid. With the big bang, time loses its infinite property on the grid. With quantum mechanics, spacetime itself might not be able to make sense below the Planck length. I hear that this quantum approach to spacetime might provide a solution to Zeno's paradoxes or those paradoxes might imply the necessity of something like the Planck length: http://barang.sg/index.php?view=achilles&part=8

Actually, I don't know.

I did finish Wolfson's text and found another by Chad Orzel called How to Teach Relativity to Your Dog. I didn't check it out, but it looks like he has upped the challenge somewhat.

Hi YesNo I have just thought of another way to the theory.
I would ask this:

Why would anyone want to teach the theory of relativity to?
I am looking for a reason.

For example I teach myself cooking because I wish to feed myself first and foremost.

I think the main reasons to teach this are to explain gravity and what the consequences are with having an upper speed limit that light can achieve.

One would either have to teach the Newtonian gravity as a force acting instantaneously through a distance or Einstein's understanding of gravity as the way spacetime is shaped around objects. Einstein's approach is more satisfying because it explains more observable phenomena, such as Mercury's orbit, and does not require that force be transmitted faster than the speed of light.

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Originally Posted by YesNo

I think the main reasons to teach this are to explain gravity and what the consequences are with having an upper speed limit that light can achieve.

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This is information that I need to think about a bit more.
I am considering the next which to define movement.
In other words what is a movement and why is there light?

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One would either have to teach the Newtonian gravity as a force acting instantaneously through a distance or Einstein's understanding of gravity as the way spacetime is shaped around objects. Einstein's approach is more satisfying because it explains more observable phenomena, such as Mercury's orbit, and does not require that force be transmitted faster than the speed of light.

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In this paragraph I am going to have to go with the word for a minute.
I need to define force and what it means in relation to speed and movement.
When I think of gravity I think a spaceman hoping/floating around space with no force to lead him.
The question I am after is what does make someone float in space and not why he/she floats?

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Originally Posted by YesNo

I think the main reasons to teach this are to explain gravity and what the consequences are with having an upper speed limit that light can achieve.

One would either have to teach the Newtonian gravity as a force acting instantaneously through a distance or Einstein's understanding of gravity as the way spacetime is shaped around objects. Einstein's approach is more satisfying because it explains more observable phenomena, such as Mercury's orbit, and does not require that force be transmitted faster than the speed of light.

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That people chose to try to explain Newtonian gravity as forces at a distance and cast it in bronze, does not mean that Newton or Galileo ate that tangerine. Neither do we eat the super darn stringettas. And the unified field pee?
The future lies in the understanding of densities and objects moving through them. The speed of light could be any. We'll proceed to eliminate the ridiculousness of weak proof (axion of choice), the idiocy of forces at a distance, or Italian cheese and stringettas, unified pee and the like. There is not enough magic, no enough elegance, not enough theater in all that poor man's stuff. Magic is a science.

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Originally Posted by cacian

In this paragraph I am going to have to go with the word for a minute.
I need to define force and what it means in relation to speed and movement.
When I think of gravity I think a spaceman hoping/floating around space with no force to lead him.
The question I am after is what does make someone float in space and not why he/she floats?

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They float due to lack of gravity. All bodies exert gravitational pull, if you have a larger mass the force will be stronger. Hence why on Earth we walk 'normally', on the moon spacemen can sorta 'bounce' along, as the moon has a smaller mass.

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Originally Posted by YesNo

I didn't realize that there were "atomic force microscopes"...

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You could have some great kids activities based around that idea. Blindfold them, give them a stick and see if they can "see" objects by feeling them with the stick. Could lead to some really cool questions, like: Are blind people really blind?

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Originally Posted by YesNo

On a theoretical level the spacetime grid seems like it should be flat and allow one to go out to infinity in both the space and time dimensions since nothing logically stops us from doing so.

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Why should it be flat? Einstein's GR predicted three possible states - flat, closed curvature, open curvature. Flat and open go to infinity, closed is a three dimensional spherical surface in a four dimensional space. Head off in a spaceship and you don't go to infinity you come back to where you started (like flying a plane away from your city...)

That said, observational astronomers are now pretty certain the space is flat, and that the universe will expand forever so it looks like space and time are indeed infinite as you say.

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Originally Posted by YesNo

I did finish Wolfson's text and found another by Chad Orzel called How to Teach Relativity to Your Dog.

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Now that's just silly!

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Originally Posted by Volya

They float due to lack of gravity. All bodies exert gravitational pull, if you have a larger mass the force will be stronger. Hence why on Earth we walk 'normally', on the moon spacemen can sorta 'bounce' along, as the moon has a smaller mass.

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You're right about the 'bouncing' moon men, but not right, or at least not clear enough for a twelve year old, about floating being due to 'lack of gravity'. So how to explain floating astronauts to a twelve year old? Here's an attempt:

There is only "zero gravity" at special points in space where gravity cancels out - if the moon and the earth were the same size that would be the mid-point between them.

The reason astronauts in earth orbit seem to float is that they are in free fall.

Imagine an aircraft's engines cut out and it just free falls to Earth. The passengers would fall at the same speed as the plane and appear to be floating. In a spacecraft it's exactly the same thing, but the forward velocity of the spacecraft means that it never hits ground, it just remains in orbit.

On firing the rockets and heading to the moon the astronauts feel a force "like gravity" due to the acceleration. But on turning off the rockets they free fall to the moon - the rocket and the astronauts fall at the same speed towards the moon, and therefore the astronauts seem to be floating. But there is no "lack of gravity". The gravitational field of the moon and the Earth are acting, and there is a pull towards the Earth or moon, depending on the distance from either.

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Originally Posted by Volya

They float due to lack of gravity. All bodies exert gravitational pull, if you have a larger mass the force will be stronger. Hence why on Earth we walk 'normally', on the moon spacemen can sorta 'bounce' along, as the moon has a smaller mass.

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I am not so sure about size and mass because it is relative.
Man earth Man moon mass/size way is proportionate .
A man bouncing on a moon is like a tennis ball bouncing on the floor.
The same idea.
I am thinking along the line of earth is populated and moon is not.
Earth weighs more then moon.
The bouncing effect is to the 'empty 'effect.
There is weight distinction between empty space and man. The element of air plays a role too.
Man breaths on earth but does not on the moon. This indicates something. The reason I am guessing that men bounce on the moon just like a tennis ball on earth is because of lack of oxygen in both their system.

No cacian. The moon just simply 'weighs less' than the earth effectively.

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Originally Posted by mal4mac

You could have some great kids activities based around that idea. Blindfold them, give them a stick and see if they can "see" objects by feeling them with the stick. Could lead to some really cool questions, like: Are blind people really blind?

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It is amazing that we can get more information about something than we might expect we could.

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Originally Posted by mal4mac

Why should it be flat? Einstein's GR predicted three possible states - flat, closed curvature, open curvature. Flat and open go to infinity, closed is a three dimensional spherical surface in a four dimensional space. Head off in a spaceship and you don't go to infinity you come back to where you started (like flying a plane away from your city...)

That said, observational astronomers are now pretty certain the space is flat, and that the universe will expand forever so it looks like space and time are indeed infinite as you say.

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I was trying to think of what space and time might be like without matter or energy. I doubt that space and time could really exist without them, however.

Now that the universe has started, does it go on forever or will matter and energy decay at some point into nothing destroying space and time when it is all gone?

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Originally Posted by mal4mac

The reason astronauts in earth orbit seem to float is that they are in free fall.

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Right. That seems like the normal frame of reference that general relativity claims all physical laws have to be valid in.

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Originally Posted by cafolini

That people chose to try to explain Newtonian gravity as forces at a distance and cast it in bronze, does not mean that Newton or Galileo ate that tangerine. Neither do we eat the super darn stringettas. And the unified field pee?
The future lies in the understanding of densities and objects moving through them. The speed of light could be any. We'll proceed to eliminate the ridiculousness of weak proof (axion of choice), the idiocy of forces at a distance, or Italian cheese and stringettas, unified pee and the like. There is not enough magic, no enough elegance, not enough theater in all that poor man's stuff. Magic is a science.

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I don't know what they might have accepted.

If magic is in some way repeatable, I suspect it could be a science. People would probably not call it magic anymore.

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Originally Posted by YesNo

I don't know what they might have accepted.

If magic is in some way repeatable, I suspect it could be a science. People would probably not call it magic anymore.

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It is well known that magic is a science borrowing from many fields. You should dig into it. I'll close this case with that. It's irrelevant what people that cannot grasp it call it. For those who are magicians, it is more magic than ever.