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fredreload
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Does length contraction means the contraction of space time?
No. It cannot be that, because we all occupy the same spacetime yet we don't all observe the same length contraction.fredreload said:Does length contraction means the contraction of space time?
Looking at the twin paradox, the effect of the twin in acceleration is there that the twin on the spaceship does experience a time dilation. Right, I'll take some time to review thisNugatory said:No. It cannot be that, because we all occupy the same spacetime yet we don't all observe the same length contraction.
Length contraction is a natural result of the relativity of simultaneity. The length of an object is the distance between where its ends are at the same time, so when things that are at the same time for one observer are not at the same time for another observer, they will find different lengths.
No, NOBODY ever "experiences" time dilation, It is something you see in objects that are moving relative to you but they see YOU as time dilated at the same time you see them as time dilated.fredreload said:Looking at the twin paradox, the effect of the twin in acceleration is there that the twin on the spaceship does experience a time dilation. Right, I'll take some time to review this
fredreload said:Looking at the twin paradox, the effect of the twin in acceleration is there that the twin on the spaceship does experience a time dilation. Right, I'll take some time to review this
Hmm, the result of the twin paradox is that the person moving away from Earth experience a slower time when traveling close to the speed of light. Therefore when the twin on Earth ages 10 years, the twin traveling on the spaceship only ages 6 years by traveling toward a fraction of the speed of light. The same thing happens with gravitation time dilation as the person closer to Earth experiences a slower time passing by then the one away from Earth by a few nanosecond.Nugatory said:The twin paradox is an example of differential ageing, a different phenomenon than length contraction and time dilation. One way of seeing that it is different from time dilation is to consider teh time dilation that is present in the twin paradix: at every point in the journey, the traveling twin is at rest relative to himself while the stay-at-home twin is moving; therefore the stay-at-home clock is the time-dilated one as far as the traveller is concerned. However, traveller is still able to correctly calculate that he will age less than stay-at-home - even though stay-at-home's clock is dilated throughout the journey.
No, the person on the spaceship does NOT experience slower time. He/she experiences time passing at one second per second just as does the stay-at-home. What happens is that the person on the spaceship takes a different path through space-time and therefore experiences fewer ticks of his one-second-per-second clock than does the stay-at-home.fredreload said:Hmm, the result of the twin paradox is that the person moving away from Earth experience a slower time when traveling close to the speed of light. Therefore when the twin on Earth ages 10 years, the twin traveling on the spaceship only ages 6 years by traveling toward a fraction of the speed of light. The same thing happens with gravitation time dilation as the person closer to Earth experiences a slower time passing by then the one away from Earth by a few nanosecond.
Well yes neither of the twins would experience a slower time, it feels shorter for one 6 years, and longer for the other one 10 years. I am thinking that speed causes space time to contract through length contraction matches the fact that the person on Earth with a more compact space time has a time dilation. If gravity increases with a more compact space time the result would be more prominentphinds said:No, the person on the spaceship does NOT experience slower time. He/she experiences time passing at one second per second just as does the stay-at-home. What happens is that the person on the spaceship takes a different path through space-time and therefore experiences fewer ticks of his one-second-per-second clock than does the stay-at-home.
EDIT: and by the way, this is one of the most confusing things when you first start to look into special relativity so you're in good company not getting it right away.
fredreload said:Hmm, the result of the twin paradox is that the person moving away from Earth experience a slower time when traveling close to the speed of light.
fredreload said:Well what Wikipedia says on time dilation is that "The laws of nature are such that time itself (i.e. spacetime) will bend due to differences in either gravity or velocity – each of which affects time in different ways." I'm still skeptical about how velocity bend time, I'm not sure if it's mass related
The sentence is just plain flat-out wrong.fredreload said:Well what Wikipedia says on time dilation is that "The laws of nature are such that time itself (i.e. spacetime) will bend due to differences in either gravity or velocity
I thought it was both RoS and time dilation? What do you call it when you travel to Alpha Centuari at 90% of the speed of light and measure the distance traveled to be 2 LY (if I did that math right...).Nugatory said:Length contraction is a natural result of the relativity of simultaneity. The length of an object is the distance between where its ends are at the same time, so when things that are at the same time for one observer are not at the same time for another observer, they will find different lengths.
It's hard to separate the two - but I can say that the distance between Earth and Alpha Centauri is pretty much by definition the distance between where the Earth is right now and where Alpha Centauri is right now. That definition works whether I'm at rest relative to them or not, and yields the appropriately contracted length if I am not.russ_watters said:I thought it was both RoS and time dilation?
My usual example is how do you measure the length of a beetle? You just stand it on a ruler and read off the position of its head and the position of its tail. If the beetle is walking, though, that procedure will not get you its length if you don't make the measurements at the same time. In that example, failing to measure simultaneously could just be sloppy experimentalism. But the relativity of simultaneity means that there is genuine, unresolvable, disagreement over what constitutes "at the same time" in different frames (and the beetle is moving in at least one of them), and that's where length contraction comes from. Observers at rest in the two frames use the same procedure to measure length, but because they disagree about simultaneity they get different lengths.russ_watters said:I thought it was both RoS and time dilation? What do you call it when you travel to Alpha Centuari at 90% of the speed of light and measure the distance traveled to be 2 LY (if I did that math right...).
Isn't "an absolute rest frame" by definition the measurement of "proper length" with no distortion of observation via movement relative to the object (or distance) measured? So then the distance to Alpha Centauri or the length of a beetle is not changed by "how you look at" either in relative motion. How is the above wrong?Ibix said:My usual example is how do you measure the length of a beetle? You just stand it on a ruler and read off the position of its head and the position of its tail. If the beetle is walking, though, that procedure will not get you its length if you don't make the measurements at the same time. In that example, failing to measure simultaneously could just be sloppy experimentalism. But the relativity of simultaneity means that there is genuine, unresolvable, disagreement over what constitutes "at the same time" in different frames (and the beetle is moving in at least one of them), and that's where length contraction comes from. Observers at rest in the two frames use the same procedure to measure length, but because they disagree about simultaneity they get different lengths.
Time dilation isn't directly relevant to this, although you can't build a symmetric picture of the world without invoking ot as well - you end up with an absolute rest frame.
"absolute rest frame" is an ambiguous term. Do you simply mean a frame of reference in which is an object is at rest? If so, then leave out the "absolute" since it adds nothing but confusion. If on the other hand, you mean an absolute frame of reference against which anything's motion can be measured, then that is an incorrect concept as there is no such thing.Michael Mooney said:Isn't "an absolute rest frame" by definition the measurement of "proper length" with no distortion of observation via movement relative to the object (or distance) measured? So then the distance to Alpha Centauri or the length of a beetle is not changed by "how you look at" either in relative motion. How is the above wrong?
Michael Mooney said:Isn't "an absolute rest frame" by definition the measurement of "proper length" with no distortion of observation via movement relative to the object (or distance) measured? So then the distance to Alpha Centauri or the length of a beetle is not changed by "how you look at" either in relative motion. How is the above wrong?
The phrase, "absolute rest frame" quotes Ibix above. Of course all motion is "relative to what?," so there is no absolute frame of reference for velocity. But "proper length" always refers to length as measured from at rest with the object or distance in question. That leaves the question, "Is length variable with how you measure it or do "things" and distances have objective lengths independent of "how you look at them." (Objective vs subjective, the latter meaning frame dependent.) Measurement does not change lengths or distances. They exist objectively prior to varieties of frames of reference from which they are measured. Something to consider besides repeating the rules of orthodox special relativity/ subjectivity.phinds said:"absolute rest frame" is an ambiguous term. Do you simply mean a frame of reference in which is an object is at rest? If so, then leave out the "absolute" since it adds nothing but confusion. If on the other hand, you mean an absolute frame of reference against which anything's motion can be measured, then that is an incorrect concept as there is no such thing.
PROPER length has an absolute value but measured/calculated length is frame dependent so yes, length is variable depending on how you measure it.Michael Mooney said:The phrase, "absolute rest frame" quotes Ibix above. Of course all motion is "relative to what?," so there is no absolute frame of reference for velocity. But "proper length" always refers to length as measured from at rest with the object or distance in question. That leaves the question, "Is length variable with how you measure it or do "things" and distances have objective lengths independent of "how you look at them." (Objective vs subjective, the latter meaning frame dependent.) Measurement does not change lengths or distances. They exist objectively prior to varieties of frames of reference from which they are measured. Something to consider besides repeating the rules of orthodox special relativity/ subjectivity.
and you misunderstand, apparently, the way in which he used it, which was to say somewhat indirectly what I said specifically in post #20 which is that there IS no such thing as an absolute frame of reference.Michael Mooney said:The phrase, "absolute rest frame" quotes Ibix above
You are correct that there is one frame in which the beetle is at rest, and all observers agree what that frame is and what length the beetle is in that frame. As Nugatory and phinds have said, though, that is only a special frame for that one beetle, not for beetles in general nor for the laws of physics.Michael Mooney said:Isn't "an absolute rest frame" by definition the measurement of "proper length" with no distortion of observation via movement relative to the object (or distance) measured? So then the distance to Alpha Centauri or the length of a beetle is not changed by "how you look at" either in relative motion. How is the above wrong?
If that were true then the distance to Alpha Centauri (or to the Sun) and the length of Earth's diameter would vary with how you measure it. However, in fact astronomy and Earth science have determined those distances and that length very precisely. The actual distance between stars (astronomically speaking) does not change with all possible varieties of measurement frames, nor does the nearly spherical shape of earth.phinds said:PROPER length has an absolute value but measured/calculated length is frame dependent so yes, length is variable depending on how you measure it.
All those things are different when measured in different frames of reference. Proper length is invariant, but it isn't always what it is "natural" to measure.Michael Mooney said:If that were true then the distance to Alpha Centauri (or to the Sun) and the length of Earth's diameter would vary with how you measure it. However, in fact astronomy and Earth science have determined those distances and that length very precisely. The actual distance between stars (astronomically speaking) does not change with all possible varieties of measurement frames, nor does the nearly spherical shape of earth.
Michael Mooney said:If that were true then the distance to Alpha Centauri (or to the Sun) and the length of Earth's diameter would vary with how you measure it. However, in fact astronomy and Earth science have determined those distances and that length very precisely. The actual distance between stars (astronomically speaking) does not change with all possible varieties of measurement frames, nor does the nearly spherical shape of earth.
I think you are misunderstanding the entire topic of this thread, which has nothing to do with the accuracy of measurements but rather the differences in what is seen from different frames of reference.ebos said:My 2 cents would add that there are levels of reality (measurement) which are "good enough" for what we are measuring at the moment. I would certainly agree that there is really no such thing as precise measurement. But there is measurement that is 'good enough' for our purposes at the moment we need them. Like I wouldn't need to know anything about quantum distances if I was sending a payload to the ISS. There are measurements available that are good enough. More than good enough, actually, because out standards are usually double or triple what we really need for accuracy or safety. But I wouldn't use my metre-stick (just doesn't sound as good as yard-stick) to measure the wavelength of a red light, or whatever. That's why it's called 'relativity' I guess.
It's also got to do a bit with attitude. For example some of us are just more subjective than we are objective (I find engineers tend to be more objective, but that's me). Then, of course, we start to approach uncomfortable areas like, dare I say it, meta-physics.
Jump in anytime to correct me, folks. Have a good one.
Yeah, well I thought it looked pretty easy, peasy. Must be that new BP med.phinds said:I think you are misunderstanding the entire topic of this thread, which has nothing to do with the accuracy of measurements but rather the differences in what is seen from different frames of reference.
That is, your post is perfectly reasonable, it's just completely irrelevant to the topic at hand.
Length contraction is a phenomenon in which an object's length appears to decrease when it is moving at high speeds relative to an observer. This is a consequence of Einstein's theory of special relativity, which states that the laws of physics are the same for all observers in uniform motion.
While length contraction refers to the apparent decrease in length of a moving object, space-time dilation refers to the slowing down of time for a moving object relative to an observer. They are both consequences of special relativity, but they are two distinct phenomena.
Yes, length contraction is only noticeable at speeds close to the speed of light. At everyday speeds, the difference in length is too small to be observed. This is because the effects of length contraction are dependent on the speed of the object relative to the observer.
No, length contraction is not noticeable in everyday life as the speeds at which we move are much slower than the speed of light. However, it can be observed in particle accelerators and other high-speed experiments.
Length contraction challenges our traditional understanding of space and time as fixed and absolute. It shows that an object's length can appear different to different observers depending on their relative speeds. This is a fundamental concept in the theory of special relativity and has greatly expanded our understanding of the universe.