Relativity acceleration paradox?

[Qfwfq]

It is valid in reality. Look up inertial coordinate systems and so-called apparent forces.

....

 

I'm reading quite bit on SR right now in order to try to gain a better understanding of it so I really can't look up your reference at this time.

If you don't understand what is meant by inertial frame of reference (or coordinate system) then you are neglecting something very fundamental toward understanding what you are talking about. I would suggest you take the time out.

 

However, if you want to quote it or better explain your position here, I'd be very interested. Can you also explain how it would not alter the earth's rate of orbit around the sun? Oh wait, in order to do that the person falling has to have a force strong enough to move not just the earth, but the sun and all the stars by the same degree. I'm listening....?

Quite right. Still listening? Here goes:

 

For the falling observer, the whole universe is accelerating, instead of him, the opposite way. Why is his point of view wrong and the other one right?

 

Up to and including special relativity, we say that the falling observer's coordinates are not inertial. This is very different from saying that they are wrong. The laws of dynamics are valid in the non-inertial coordinates but only with an ad hoc alteration, an extra term with the opposite acceleration. The extra term is equivalent to a force, applied to any object having mass, as well as "other" forces; this extra force is called an apparent force.

 

"A trick! A mere, sly trick!" you will now cry out. Which system of coordinates is inertial, then? Find one! ;)

 

The one defined by your bedroom floor and walls is not inertial, although it is less non-inertial than the falling observer's coordinates. Earth is rotating, look up Coriolis forces and Foucault's pendulum. Tormod's reply was about the common centre of mass of Earth and the falling object, this defines a "better" reference than Earth's surface. An example of this is Earth and Moon, they are orbiting around their common c. m., but this is also orbiting around the Sun so it isn't a perfect inertial system. Neither is the Sun, the c. m. of the solar system is better. The c. m. of the Milky Way is even better, but it is surely a bit accelerated by the other galaxies. Does anybody have any info about the centre of mass of the universe? ;)

 

Moreover, a gravitational field, the very one that "is accelerating" your falling observer toward the Earth, can be viewed, at least locally, as the exact same "trick" as above, an apparent force.

[C1ay]

I am not saying that the person would alter earths orbit necessarily, although this would be the case if he fell from a polar position. If he fell from an equatorial position he would have to either speed up or slow down the earth's position IN its orbit, depending on if he feel behind the earth or in front of the earth in it's direction of travel around the sun.

What difference would the position he fell from make?

 

You also give the impression here that you think the equatorial plane is the same as the orbital plane. It's not.

[ldsoftwaresteve]

Ewright: I understand what you are saying abuot the color in my television, but if you look at my television in a mirror, blue is still blue but it's not a real T.V.

Interesting point. So, are you saying that you think Einstein was figuratively looking in a mirror when he developed his theories?

[Erasmus00]

 

The one defined by your bedroom floor and walls is not inertial, although it is less non-inertial than the falling observer's coordinates.

 

Actually, in GR, the free-falling observer is in an inertial frame. The room on the Earth is not.

-Will

[Qfwfq]

That's where I was hoping to get with my argument.

 

The next step is: why are astronauts orbiting Earth said to be "in zero-g"? They're not much further from the centre of Earth than we are.

[Tormod]

The next step is: why are astronauts orbiting Earth said to be "in zero-g"? They're not much further from the centre of Earth than we are.

 

Uhm, is this a real question or a trick question? :wave:

 

Anyway, zero-g is the wrong term. Technically they are in microgravity. They are in free fall but are still being pulled by Earth's gravity.

[Qfwfq]

Technically they are in microgravity. They are in free fall but are still being pulled by Earth's gravity.

How micro is that gravity, and how much of Earth's gravity are they being pulled by?

[Tormod]

How micro is that gravity, and how much of Earth's gravity are they being pulled by?

 

It will depend on their distance to Earth, but as long as they are not within the gravity well of another object (say, the Moon or Mars), the Earth will pull at them. In low orbits, for example where the space shuttle or ISS is (400-600 km), there is still atmospheric drag and things tend to go lower and lower. The ISS requires boosts every 6 months or so in order to maintain it's orbit. For those unaware of how orbits work, the ISS is not "lifted" but given a speed increase along the orbit using for example a Soyuz craft. This acceleration gives the ISS a higher altitude.

 

Only when an astronaut is in orbit at a high enough altitude (ie, well above the atmosphere) will there be no noticable fall towards the planet since there will be no drag.

 

For all practical purposes, though, the astronauts are in "near" zero-g. Gravity is inherently extremely weak, as we know.

 

NASA has some more info on this:

http://www1.msfc.nasa.gov/NEWMSFC/gravity.html

[Qfwfq]

This means that the tiny gravity is due to the craft not being in perfect free fall. If they were within the gravity well of another object such as the Moon or Mars, they wouldn't very well be orbiting the Earth.

 

If, otoh, there were no air resistance at all at a few hundred kilometres altitude, they'd be in perfect zero-g although their distance from Earth's centre isn't all that much greater than ours, which is about 6300 km.

[EWright]

Interesting point. So, are you saying that you think Einstein was figuratively looking in a mirror when he developed his theories?

 

By George, think he's got it!

[EWright]

OK people, we're getting a bit off topic here. I've been out of town for the week and am just catching up. Orbiting is simply a balance between gravity's influence and a rate of speed stronger than earth's gravitational pull and weak enough that it doesn't break earth's gravitational pull and head out into space. When this is achieved the object is basically falling around the earth... it's essentially falling towards the earth but at a speed that keeps it moving forward at a rate too fast to allow it to be pulled downward towards the earth's surface. Now back to the topic at hand please.

[EWright]

You do realize that several members of the physics community have created alternative theories to Einstein's. To date, all experimental evidence supports Einstein, not others.

 

As to the complicated theories, general relativity does indeed requires learning differential geometery, a rather difficult branch of mathematics. However, special relativity can be understood using only basic calculus. And anyone with the inclination to learn it has countless introductory textbooks to choose from. You never have to accept what they teach, if you are willing to put a bit of work into learning the math. And if you aren't willing to do the work, how are you going to formulate a theory of your own?

-Will

 

It is not about doing the math to formulate a theory, as I have no doubt this can be done. When Einstein, Hawking, and others develop their initial theories/ideas, it is generally not done at a chalkboard developing equations. Instead, they are usually pondering the nature of how things work and develop an idea or theory. Only later is the math formed to fit the idea. This is where Einstein errored. He forced the mathamatics to fit the ideas he had. Because they describe what really happens, he did formulate mathamatical theories that do work to DESCRIBE the universe. However, as has been pointed out in this thread, relativity "speaks" in "metaphores".

 

Inertial frames are based on PERSPECTIVE. They are not actual. They are akin to driving a stickshift car on a hill and looking to your right at another car while you are stopped at a light. You see the car begin to pull ahead and wonder why it is doing so when there is a red light. SR says if you are viewing no other frames of reference, you have just as much right to say you are moving as you are to say he is moving. And when you unexpectidly slam into the car behind you, you realize it was indeed YOU who were moving and that the other car was not actually running the red light. Slamming into the car behind you, which was not in your field of view at the time (I'm loosely attempting to refer to an inertial force here, so please don't give me the specifics of this car technically being in the same inertial frame) is the wakeup call that SR is long overdue for.

[EWright]

Then propose your theory to us, and we shall see. If your theory is as revolutionary as you make it out to be, it should sway us. But why keep playing these silly games? "My theory answers this" doesn't mean much untill you are willing to demonstrate.

-Will

 

I would very much like to do this. However, I'd like to put it out in a more "meaningful" way. This is to say, I'd prefer to find a way to publish the theory. I do realize this is a challenge because i'm not affiliated with a research institution; nor do I have the formulas to back up the theory.

 

Ideally, I'd like to get the idea published as just that -- ideas and concepts, that the actual science community can then work with to develop the math to prove or disprove. I do understand that I can propose it as it is and that it will be peer reviewed, but I do not know if any journals will consider publishing it even then, if I am not affiliated with a research instituation. If any of you have any advice on this, I'd be very interested in what you have to say. I do have a few thoughts on it myself.

 

I am currently reading some material on physics and relativity to give myself a better understanding. I'd like to gain enough of an understanding of the mathamatics behind it that it would make sense to me in that way as well, and that I might then be able to formulate my theory this way. I can invision it as being mathamatically provable based on my limited understanding of physics, but I can not yet put it into such form.

[EWright]

EWright, suppose you were in a space ship, say in the middle of one of the gaps between clumps of galaxies. You could see no stars, no points of reference, totally unable to determine your motion with respect to anything. All of a sudden you see another ship approaching your ship. Now from your frame of reference you will claim that the other ship is the one that is moving toward you, when in fact you can not predict which is the true reality.

 

I always find it humorous that a theory that strives to explain the truest nature of things, must remove all stars, planets and any other matter or reference point in order to make itself work. See my post above about the stickshift car scenario.

 

Even without any reference points, the fact is that in your spaceship scenario, you can tell. The REALITY of the situation is that an amount of force was necessary to set one or both ships in motion. If no force was ever exerted on one ship, it's pilot can safely KNOW that he or she is the stationary one. Also, physics should tell an educated pilot who's ship WAS put into motion by some force, exactly how fast he should be traveling. If this is so, then he can deduce between the speed of his ship and the ship that he is approaching, whether it is still or if in motion, at what speed it is moving relative to his own as well. (This is assuming he doesn't mix his standard and metric calculations, causing him to crash into the only other ship in an otherwise empty universe.)

[EWright]

For the falling observer, the whole universe is accelerating, instead of him, the opposite way. Why is his point of view wrong and the other one right? [/Quote]

 

It is different. It is a matter of force. If SR is right, I can stab a man but tell the judge that I was just holding the knife and that he and the rest of the universe shifted, causing him to suddenly move into the blade. I just hope the judge is brushed up on his modern day physics. Hmmm... maybe a career as a defense attorney is a good idea.

[Erasmus00]

This is where Einstein errored. He forced the mathamatics to fit the ideas he had. Because they describe what really happens, he did formulate mathamatical theories that do work to DESCRIBE the universe. However, as has been pointed out in this thread, relativity "speaks" in "metaphores".

 

If you develop math around a wrong idea, then when you make predictions, they end up wrong. Relativity doesn't "speak in metaphore" it speaks in mathematics. All physics does.

 

Inertial frames are based on PERSPECTIVE. They are not actual.

 

This sentence doesn't make any sense, really. Are you saying you can't construct an inertial frame? To go to the car example you gave: three men are on trains, the trains are on very smooth tracks. One man's train is moving forward on the tracks at a constant speed, one backward at a constant speed, one is sitting still. What test can these men do to figure out what train they are in?

-Will

[EWright]

If you develop math around a wrong idea, then when you make predictions, they end up wrong. Relativity doesn't "speak in metaphore" it speaks in mathematics. All physics does.

 

 

 

This sentence doesn't make any sense, really. Are you saying you can't construct an inertial frame? To go to the car example you gave: three men are on trains, the trains are on very smooth tracks. One man's train is moving forward on the tracks at a constant speed, one backward at a constant speed, one is sitting still. What test can these men do to figure out what train they are in?

-Will

 

You might want to stick to just two trains if you want to make this challenging. If you include three trains and they can see each other on paralell tracks, the answer seems obvious. For two trains, see my post above about the space ship scenarios.