Physics – Relativity

Common…. Does anybody here not understand the theory of relativity?!?

and volvie correct me if im wrong- but hasnt it been proven that its actually the earth that revolvs around the sun as it spins on the axes of the universe. and its just realative as to how fast it moves. it could be im wrong but thats what i thought scientists proved.

someonesboard, Copernicus is the one who postulated and changed sciences viewpoint, that the Earth rotates around the Sun. Before Copernicus, for most of history science said the Sun circles the Earth. Newton changed sciences viewpoint again, and said that Earth and Sun rotate about a common center of gravity. Einstein changed it again. He described the General Theory of Relativity – in which all motion is relative. In General Relativity, you can use any frame of reference. Relative to humanity, the Sun revolves around the Earth. To put it more simply, all motion is relative. Relative to humanity, the Earth is not rotating.

thats the theory of general realativity. but then theres the deeper theory of speacial realativity.

General relativity is more advanced than special relativity and is only taught in detail in certain postgraduate physics programs. Special relativity is taught earlier in less advanced programs.

It is a bit harder to explain stellar parallax from the perspective of an Earth-fixed reference frame than from the perspective of a solar system barycentric reference frame. But it’s not all that hard to explain stellar parallax from the perspective of an Earth-centered frame. The motion of the stars can be explained in terms of the “third body effect”. People who model the behavior of satellites in Earth orbit vastly prefer to use an “Earth-centered inertial” reference frame (a non-rotating reference frame with origin at the center of the Earth) than a barycentric frame. From the perspective of such a reference frame, the Sun and Moon (and the planets) make the satellite’s orbit not quite Keplerian. The perturbation is explained by a pseudo-force called the third body effect.

Phases of Venus anyone?

The Wolf

You didn’t answer the question. How do you, or einstein, account for the necessary yet impossible speed of the celestial bodies revolving around the earth?

And besides, the principle of equivalence only pertains to linear acceleration not rotational acceleration.

I have no problem accepting that the heavens revolve around the earth, but if you want to show this is so according to the principles of science then do so honestly or admit you don’t know the answer, and hope to eventually find it.

I think he said that beyond the speed of light there is no time, but at the speed of light there is time.

Health,

I think you might be referring to the time-dilation effects of near-light-speed travel. However, there is no such thing as “beyond the speed of light.” Nothing can travel faster than the speed of light as it would acquire infinite mass and require infinite energy to get up to that speed. Unless your last name is “Kirk” or “Picard” have a warp drive, of course. 🙂

The Wolf

“its actually the earth that revolvs around the sun as it spins on the axes of the universe. “

Doesn’t the Gemara say the opposite?

Old joke that explains theory of relativity:

finding seven hairs in your cup of coffee vs. seven hairs on your head.

You decide whether it’s the general or special or spatial theory of relativity.

But of all topics in physics, why did you choose one of the most complex?

I’m glad there’s nothing else bothering you.

Just a few points:

3) If I remember correctly, once space travel became a reality, and the previously unheard-of speed of 25,000 MPH was achieved, it was proven that time actually slows down as speed increases.

WolfishMusings-

I could be wrong on this, but I’m fairly certain you need to go faster than 25K MPH to see the effects of time dilation.

Unfortunately, I don’t remember where I saw it, but I recall reading that a small but measurable time difference did occur. B”N I’ll do a little research (google) later.

the speed at which you can measure the time difference is of course dependent on the sensitivity and accuracy of the time measuring device. You can measure the effect on a moving snail if you have a good enough device…80

Any technological advances that will allow FTL travel will probably not involve altering this law of physics, but rather with warping space and/or time in some way.

I’ve heard the term “worm hole” used with regards to this, similar to “tesseract” re: time travel, but who knows?

Bonus question: What was the first man-made object to move faster than the speed of sound?

1) The X-1 (level flight)

2) The P-38 (in a dive – this is where it was proven that an aircraft could withstand supersonic flight, although the controls froze, due to the shock wave, IIRC).

3) A bullet (no human aboard [except for in the book From the Earth to the Moon, speaking of books]).

4) A cracked whip’s tip (not the entire object, but a portion of it).

5) Anything man-made, since the Earth orbits at @66,000 mph, and rotates at @1,025 mph at the equator.

6) ?

To the wolf and who ever’s bored,

I did a net search about this. First of all, a couple of years ago, a few German scientists got some photons to move faster than the speed of light. And I stand corrected, at the speed of light there is no time for matter, but since light has no matter, it still would be considered within “time”. (Because of this, no one has got anything with mass to go the speed of light, because it would require an infinite amount of energy. Also, the mass would be infitismly small.) LIGHT- It was there a little bit ago -now it’s here. It was there 10 light years ago -now it’s here; so we can see that star or whatever. Do a net search – there are a lot of easy explanations of his theories to be found. I’m so happy my college didn’t require me to have Physics.

To the guy who’s bored,

I’m not. (Also, I’m not bored.) But I think others answered your original question. If that doesn’t satisfy you -do a net search. There are many sites that put it on an easy level. I’m coming to answer your second question.

from wikipedia

Tachyon

In special relativity, while it is impossible in an inertial frame to accelerate an object to the speed of light, or for a massive object to move at the speed of light, it is not impossible for an object to exist which always moves faster than light. The hypothetical elementary particles that have this property are called tachyons. Their existence has neither been proven nor disproven, but even so, attempts to quantize them show that they may not be used for faster-than-light communication.[23] Physicists sometimes regard the existence of mathematical structures similar to tachyons arising from theoretical models and theories as signs of an inconsistency or that the theory needs further refining.[24]

the question was: “does anybody here understand the theory of realativity??”

I think the question HAS been answered. The answer is NO

Even if you could run fast enough, I think you would lose the weight as you stopped running. But you would still be physically younger (or older?) than you would have otherwise been.

I don’t understand it at all, it may be that no one understands it in a real sense, but this is what I understand from Dr. Gerald Schroeder’s book: “The Science of G-d”

If you were to travel on a light beam that leaves a star 100 light years away from earth.

You look at your watch as you leave the star, you look at it again when you arrive on earth, ZERO time will have passed for you and for your watch. But to the people on earth, if they could somehow have observed your voyage, they would measure that 100 years had elapsed from the time you left the star until you got here. Something like that.

Depends on the persective of the system you are in relative to the other system of interest. I think that is also kind of the nutshell of the theory in general

So you want to understand Relativity

Okay, here’s a basic introduction to the subject

http://en.wikipedia.org/wiki/Introduction_to_mathematics_of_general_relativity

Sorry I would have commented sooner but I had a crazy busy day.

First of all do not try to understand relativity without understanding Newton’s laws of motion. It would be like trying to study Kaballah without knowing Tanach first. (though with more math) Every physics department in the world starts by teaching Newtonian physics, I know mine did.

One important point about both SR and GR is that they do not get rid of Newtonian mechanics, but extend it. Newtonian mechanics are a special case of relativity. In the case where the object is moving slowly or not near a VERY large gravity field Newtonain mechanics and relativity give EXACTLY the same results. In terms of the solar system the only place where they give different results is in terms of the precession of the perihelion of the planet mercury, and that effect is measured in 10’s of arc-seconds per century.

It terms of time dilation the amount time slows down on a moving body is with a factor of the sqrt(1-v^2/c^2). So the closer you can get to the speed of light the easier that is to measure. In terms of subatomic particles which can get VERY close to c it is quite easy to measure. In terms of more macroscopic particles it is harder. But the best atomic clocks can be accurate to 1 part in 10^14, so for example an atomic clock on a GPS sat in orbit will not run the same as a clock on the ground. The effect is small but it is there.

GR came about when Einstein decided to ask a very simple question, he noticed that gravitational mass and inertial mass are always the same and wondered why that should be so. He then spent 10 years working out the math to turn it into something that you could actually use, and missed the chance to predict the big bang 15 years before Edwin Hubble found it.

If people have specific questions please ask them and I will try to respond (or ask someone who would know)

Let’s try to clear up a couple of things.

First off, regarding the orbit of Earth, I always notice a big confusion. There are two aspects: The yearly orbit around the sun, and the daily revolution.

When speaking about how relativity reconciles the two, we must realize that that applies to the yearly orbit. That doesn’t help anybody stick up for Chazal since they are never referring to this orbit. For all you know, they would agree that Earth revolves around the sun once a year.

As far as the daily revolution, dd already (finally) explained that we actually can prove that the earth rotates by testing the effects of centrifugal force.

Now, back to relativity. Let’s understand, that the whole thing started when it was noticed that light always seems to be traveling at the same speed, even when you are traveling away from it.

Based on this, Einstein decided that the speed pertains to how fast it will get to you. Since light, he says, travels at top speed, it will always get to you at the speed of light. This should answer someonesbored and Mod-80.

If it makes sense in our frame of reference then it makes sense. As far as we are concerned, we are going around the sun and everything else stays put.

By the way, the issue Mod-80 brings up reminds me of Rav Saadya Gaon’s Kasha/Raya that if the the universe is infinite, then that would mean that the far ends of the universe travel an infinite distance every day. Traveling an infinite distance would, of course, take forever. Therfore, it would never get back.

Another way to by; although people today still discuss the issue of what revolves around what, based on Mamarei Chazal, it would be interesting to note that the Maharal, who wasn’t that much later than Copernicus actually embraced the idea. That is without all the present day evidence. He writes in the fifth (I think) Perek of Nesiv Hatorah, that “someone recently came up with a new neat Astronomy that turned the whole Astronomy of all the years on its head.”

That, to me, sounds like he liked it. And we all know that the Sifrei Maharal are dedicated to honoring the words of Chazal. I know that bringing up this topic causes the thread to be closed, but I couldn’t help it. I never got a chance to mention these points anywhere before the thread closes.

So, quick! Somebody, change the topic back.

To all,