Cosmobrain said:GR is pretty much the same thing. However, it includes acceleration and gravity.
Cosmobrain said:objects affected by it are actually inert.
Cosmobrain said:When you're in a strong gravitational field, time will seem to run slower for you in the point of view of an observer outside.
physicist2 said:How can I explain to someone who has only high school level of education in physics, what is general and special theory of relativity about?
physicist2 said:Special theory of relativity ...
physicist2 said:General theory of relativity …
Fine. Ok then, then it just can't handle gravityPeterDonis said:This isn't quite correct; SR can handle acceleration.
I'm saying an object is traveling in a straight line as it normally would, however, space itself is distorted, so it curves and it seems like the object was affected by a force.PeterDonis said:What do you mean by this? I'm not sure what you're referring to.
I had in mind that the object A was, say, on Earth and the and observer B was in space watching A. Object A can be the surface of the planet and B can be a GPS satellite. GPS satellites work with SR and GR.PeterDonis said:One clarification here: this is only true for certain situations, where the gravitational field is produced by an isolated body that is basically static (like a planet or star or black hole). It is not true in the more general case (such as for the universe as a whole), because there is no meaningful way to define "an observer outside" to serve as the standard against which "time running slower" is measured.
jedishrfu said:
Einstein said that all observers will measure the speed of light to be 186,000 miles per second, no matter how fast and what direction they are moving.
This maxim prompted the comedian Stephen Wright to ask: "If you are in a spaceship that is traveling at the speed of light, and you turn on the headlights, does anything happen?"
The answer is the headlights turn on normally, but only from the perspective of someone inside the spaceship. For someone standing outside watching the ship fly by, the headlights do not appear to turn on: light comes out but it takes an eternity for the beams to get ahead of the spaceship.
Take the fist one or two sentences from Wikipedia. Of course that's not enough to understand anything, but you cannot do more with one or two sentences. Alternatively you can use these short visual introductions:physicist2 said:in one or two sentences please.
Cosmobrain said:Ok then, then it just can't handle gravity
Cosmobrain said:I'm saying an object is traveling in a straight line as it normally would, however, space itself is distorted, so it curves and it seems like the object was affected by a force.
Cosmobrain said:I had in mind that the object A was, say, on Earth and the and observer B was in space watching A.
Cosmobrain said:Object A can be the surface of the planet and B can be a GPS satellite. GPS satellites work with SR and GR.
Remember we are explaining relativity in a synthesized way to a high schooler.
PeterDonis said:Yes. I pointed out that SR can indeed handle acceleration because thinking that it can't is not only a common misconception, but ignores a *huge* body of experimental evidence for SR, namely, all the experiments we do in particle physics, which involve subatomic particles being subjected to huge accelerations and behaving exactly as SR predicts.
Ok, that makes it clearer. But it still might confuse someone encountering it for the first time, because you say the object travels in a straight line and then you say it curves. I would say "the object's trajectory appears to curve and it seems like the object was affected by a force".
(I would also say *spacetime* is distorted, not space; for most cases of practical interest, such as planets orbiting the Sun or satellites orbiting Earth, the effect of space curvature is negligible; the curvature that affects the trajectory is curvature in the time dimension.)
Yes, I understood what you had in mind. I was just pointing out that GR covers a wide range of situations, of which this is only one, so that it's clear that "gravitational time dilation" is a feature of this particular situation, not of GR in general.
Then GPS is probably not a good example to use, precisely because it requires combining SR and GR (i.e., it requires understanding and combining both the effects of relative motion *and* the effects of gravitational time dilation) to correctly interpret what is going on.
Cosmobrain said:Well, write your own definition of SR and GR. It would be better ;)
Cosmobrain said:In any frame of reference, the laws of physics must be the same.
cb
Happy Recluse said:It seems that this premise gets translated into "if two observers report different things, both of the reports are true." For example, the observer bouncing a ball on a moving railroad car reports the ball moving straight up-and-down, while the stationary observer watching the ball reports it moving in a W pattern. So, how do we go from "the laws of physics are the same" to "both reports are true"?
pervect said:Similarly, if you solve for the motion of the ball using the laws of dynamics in the stationary frame and then use the laws of kinematics to transform the solution to the train frame, you must get the same solution that you get using the laws of dynamics directly in the train frame.
me said:Similarly, if you solve for the motion of the ball using the laws of dynamics in the stationary frame and then use the laws of kinematics to transform the solution to the train frame, you must get the same solution that you get using the laws of dynamics directly in the train frame.
Happy Recluse said:If your conclusion is that both reports are true, then the reports are inconsistent. One or both are false.
Are there branches of physics that explain illusions? Perhaps such a branch can explain that the stationary observer reports an illusion of the ball moving in a W pattern, while observing a ball, in a moving train, bouncing straight up-and-down.
pervect said:"If both reports are true" is a bit ambiguous. If by this you mean that a stationary observer reports motion in a W pattern, while a moving observer reports straight up and down motion, this is not inconsistent either in special relativity or in classical Newtonian physics. I don't understand why you think there is a consistency problem, consistency is guaranteed by the existence of invertible transforms between the coordinate systems attacahed to frames of reference.
Happy Recluse said:The inconsistency lies between the two reports, i.e., the ball does not move straight up-and-down and not straight up-and-down (p and not-p). One of these two reports is true and the other is false. The inconsistency occurs even if no one knows which of the two is true.
Nugatory said:However, one observer uses the words "moving straight up and down" to mean that ##\frac{dx'}{dt'}=\frac{dy'}{dt'}=0## while the other uses these words to mean ##\frac{dx}{dt}=\frac{dy}{dt}=0##. Because these statements are not the same (the primed coordinates are not, in general, equal to the unprimed coordinates) this is not a "p and not-p" situation.
It's worth noting that this is a classical physics issue, around since long before Einstein - it's Galileo's work based on the Galilean transforms.
Happy Recluse said:Is the following true: ##\frac{dx'}{dt'}=\frac{dy'}{dt'}=0## is not ##\frac{dx}{dt}=\frac{dy}{dt}=0##?
Happy Recluse said:It is true that Smith claims the pattern of the bouncing ball is straight. It is true that Jones claims the pattern of the bouncing ball is not straight. Here we agree. Is it true that the pattern is both straight and not straight?
Here's an example. Smith and Jones observe a criminal suspect. Smith says the suspect is male; Jones says the suspect is not male. No one reports that the suspect is (in fact) male and not male.
Matterwave said:A better analogy would be that Smith and Jones are both looking at a suspect from two sides. Smith says "I see a face", Jones says "I see the back of a head". Do you want to say that one or the other is wrong? They see the same thing, from two different perspectives, and have two different ways of describing the same situation.
Happy Recluse said:Thank you. With your analogy, we know that both judgments can be true: the suspect has a face and a back to his head. But suppose Smith says, "The face has a mole between his eyes," and Jones says, "The [same] face has no moles on it." Here, both cannot be true. (There might be confusion about what a mole is, but we still know that both cannot be true no matter our understanding of moles. That is Smith says, "The face has X on it," and Jones says "The face has no X on it.")
Again, using your analogy, and back to the bouncing ball, Smith says, "The ball has a red stripe on it," and Jones says, "The ball has a blue star on it." Both judgments can be true. But if Smith says, "The ball bounces in a straight line," while Jones says, "The ball does not bounce in a straight line (because it bounces in a W pattern)," both judgments cannot be true.
