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    Thread: Figuring out relativity and the universal limits

    1. #26
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      Quote Originally Posted by mettw View Post
      The problem with most explanations of Special Relativity (SR) is that they use the old "Classical" mindset to explain it. I'll try to explain it using the modern concepts of symmetry and rotation.

      Hold a pencil up horizontally. It's vertical length is very small, just a few millimeters. It's horizontal length is much longer though, say 15cm. Now rotate the pencil by 90 degrees. Now the horizontal length is only a few millimeters while the vertical length is now 15cm. That is, vertical and horizontal length are relative quantities that depend on your orientation relative to the pencil. None of this is a problem however since we know that the total length of the pencil (L) is invariant. By Pythagoras theorem:

      L^2 = x^2 + y^2

      or in 3-D

      L^2 = x^2 +y^2 + z^2

      Now, in newtonian physics space and time are two completely different things. This means that you can't rotate anything through time since time is only a single dimension and so therefore the time between two events is invariant and everyone measures the same time. In SR however it was realised that time and space are just different aspects of the same thing: space-time. That is, instead of having the 3 space dimensions and one time dimension being two completely different things they are actually both parts of a single thing - the 4 dimensional space-time continuum.

      The upshot of this is that we can now do rotations involving time. These rotations are what we call velocity. So if someone is moving relative to me then his space-time is rotated relative to mine.

      Imagine two astronauts floating in space. If they are rotated relative to one another and one sees a spanner floating horizontally (relative to him) then the other will see the spanner at some angle to the horizontal, so that part of its length is horizontal and part is vertical. We could say then that the first astronaut's horizontal axis is partly vertical relative to the second astronaut.

      In the same way a space-time rotation (that is, velocity) will make the other person's time dimension partly space relative to me and his space dimension, in the direction of his travel, is partly time relative to me. Now in the pencil example the horizontal distance got smaller while the vertical one gets larger. The same thing happens here, the space distance gets smaller (length contraction) while the time distance gets larger (time dilation). Also as with the pencil example, none of this is a problem since there is an invariant length that everyone measures to be the same value:

      s^2 = x^2 + y^2 + z^2 - t^2

      Note the minus sign on the 't' dimension. So we may disagree on the value of x, y, z or t between two events, but that doesn't matter since everyone measures the interval s between the two events to have the same value.

      So, basically, you need to stop thinking of time as being a separate thing in itself. Time is just one of four dimensions in the space-time continuum and what seems to you to be time may to me seem to be space and visa versa.

      Does that make any sense at all?
      I do understand. And I do agree as far as time being another dimension, as it relates to 3d coordinates. A simply way I look at it is; 10 seconds ago I started this reply. But I started it in a whole other area of space. I don't b elieve in space-time as a dimension that go fast for some, and slower for others; as it is observed. We have absolutely no physical proof of time being variant as it pertains to speed. One MAJOR-MAJOR paradox to me is, the simple state of motion. And the more that relativist say that crap about feeling acceleration, so that's the one that knows there moving - the more infuriated I get. And another ironic point is, of all the math that defines time dilation, length contraction, distance contraction, etc., there is no math that pertains to acceleration. NONE. So to me, it is a paradox of the twins. By Einsteins own words, how do we know who's moving!? Again, I don't buy acceleration. It's a cop-out.

    2. #27
      Xei
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      Quote Originally Posted by tonypauley View Post
      True that my friend (the planes). New studies of the data though also put the planes that were at whatever altitude, as being at the exact altitude that would cause the clocks to slow down, by as much as they did. So, was SR or GR the cause?
      As I've mentioned before, SR is just a special case of GR, the general theory. All of the strange effects of SR are included in GR. You can't accept that GR is valid without accepting SR is valid. It'd be like accepting the proof that pyramids of any base have volume (1/3)*base*height, but then saying that a triangular based pyramid doesn't have volume (1/3)*triangle*height. There are two effects in time dilation. There is the effect of a gravitational field, and there is the effect of accelerating to a relative velocity, which we can call G and R respectively. R is the dilation predicted by SR and thus GR also; G is an additional factor predicted by GR. So we predict that the total time dilation should be R + G. This is what was observed in the plane experiment. It wasn't just R, and it wasn't just G, it was the sum. Testing GR is testing SR.

      You said earlier you didn't believe in time dilation (or other interesting relativistic effects like length dilation), but you seem to accept that gravitational time dilation can occur... so there's nothing inherently repugnant you find with these concepts?

      The speed of light is assumed to "C" in any and all references. We don't know that. I did the math one time taking the speed of the Earths' rotation and revolution, and the speed of the galaxy spin, so forth. The variable of how we could possible measure viewed light, is something like (I don't remember exactly) .0001% of the speed of light. (This referring to the Michelson-Morley experiment). Basically meaning... of course the speed of light is measured as "C" in our reference frame. An analogy - if I am going 100 miles per hour in a vehicle, and I slow down .0001% of that, you will still measure me going 100 miles per hour! And yes, I know CERN can't keep anything to go faster than "C". All the above is my problems with SR, it's equations, and it's assumptions, all based on the assumed fact that light is "C" is ALL reference frames. I enjoy this conversation with you. SELL ME DUDE!
      The physicists who do these experiments are very smart guys. It's a bit presumptuous to suggest they forgot to compare the magnitudes of the speed of the Earth and the speed of light, when that was the crux of the whole experiment. The predicted difference is 0.01%, or 1/10000, which is like measuring a 100m racetrack accurate to a centimetre - tricky, but not impossible, and with advanced technology we can do far better. People had wanted to measure the variation of the speed of light before, but prior to Michelson-Morely, they couldn't, precisely because their methods of measuring the speed of light didn't have an accuracy better than 1/10000. But the Michelson-Morely experiment of 1887 had an accuracy of roughly 10 times greater than this, akin to measuring a 100m track to the nearest millimetre. This conclusively ruled any variation of light due to Earth moving relative to it. And it didn't stop with Michelson and Morely. Technology and accuracy has gotten better and better since then. The best modern experiments have an accuracy of 1/100000000000000000! And they measure no difference in the speed of light, though the variation in our motion is trillions of times larger.

      Quote Originally Posted by tonypauley View Post
      By Einsteins own words, how do we know who's moving!?
      Einstein was only asking rhetorically. This was a question which his theory answers. Though velocity is relative, acceleration is not. Accelerations are entwined with forces. We can easily tell who's moving; they're the one who fired their rockets.
      Last edited by Xei; 02-01-2014 at 05:43 PM.
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    3. #28
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      Let me put this another way. My twin zooms off at .8 'C'. Same time he/she left, I shot off a radio message. My twin, and my message, are headed for planet D. I know that planet D is (variable) away. Planet D, upon receiving my message, sends back that they have received my message, and will signal again when my twin arrives/departs.

      I know when my signal will get to planet D. I can also calculate when my twin will be there (based on C). Planet D sends me a radio signal that they have received my signal, then signals me that they have arrived, and are headed back.

      Now place any numeric value you want in (variable), Show me the math that says when my I will receive the radio transmission from D, and when my twin will show up and greet me (MY AGE/THEIR AGE). And show me where the Lorentz transformations apply to dilations and contractions of light.??? BINGO!

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      Quantum physics and mechanics a theory worth discussion, professor wikipedia.

    5. #30
      Xei
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      Quote Originally Posted by tonypauley View Post
      Let me put this another way. My twin zooms off at .8 'C'. Same time he/she left, I shot off a radio message. My twin, and my message, are headed for planet D. I know that planet D is (variable) away. Planet D, upon receiving my message, sends back that they have received my message, and will signal again when my twin arrives/departs.

      I know when my signal will get to planet D. I can also calculate when my twin will be there (based on C). Planet D sends me a radio signal that they have received my signal, then signals me that they have arrived, and are headed back.

      Now place any numeric value you want in (variable), Show me the math that says when my I will receive the radio transmission from D, and when my twin will show up and greet me (MY AGE/THEIR AGE). And show me where the Lorentz transformations apply to dilations and contractions of light.??? BINGO!
      Okay, well, let's say planet D is one light year away. So from your stationary perspective it takes one year for light to get there, and another year for it to get back - 2 years.

      Call your position the origin of frame S, and your twin's position the origin of frame S'. They are moving at velocity 0.8 relative to you, so in your frame, S, their path is x = 0.8t, and they reach planet D when x = 0.8t = 1 lightyear, which is when t = 1/0.8 = 1.25 years. So to find the time for their round trip from our perspective we just double this, which gives us 2.5 years.

      To find the time in their frame, S', when they reach planet D, we can just use the Lorentz transformation. t' = γ(t - vx) = γ(1.25 - 0.8*1) = 0.45γ, and for v = 0.8 we have γ = 1/sqrt(1 - v2) = 5/3. So t' = 0.45*(5/3) = 3/4 years, and again we just double this to find the time for their round trip from their perspective, which gives us 1.5 years.

    6. #31
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      Quote Originally Posted by Xei View Post
      Okay, well, let's say planet D is one light year away. So from your stationary perspective it takes one year for light to get there, and another year for it to get back - 2 years.

      Call your position the origin of frame S, and your twin's position the origin of frame S'. They are moving at velocity 0.8 relative to you, so in your frame, S, their path is x = 0.8t, and they reach planet D when x = 0.8t = 1 lightyear, which is when t = 1/0.8 = 1.25 years. So to find the time for their round trip from our perspective we just double this, which gives us 2.5 years.

      To find the time in their frame, S', when they reach planet D, we can just use the Lorentz transformation. t' = γ(t - vx) = γ(1.25 - 0.8*1) = 0.45γ, and for v = 0.8 we have γ = 1/sqrt(1 - v2) = 5/3. So t' = 0.45*(5/3) = 3/4 years, and again we just double this to find the time for their round trip from their perspective, which gives us 1.5 years.
      Which goes back to my original post... Einstein said, and yes, it has been proven, that the speed of light is C is OUR REFERENCE FRAME. There has not been 1, notta, zilch, experiement ever done to confirm that C is constant in ALL frames. Of course we, and every experiment ever known to man, will always show light to be C. It's obvious. And it's obvious that my twin, zooming towards D @ .8C, will measure the distance to be smaller. In a way, what we have done, is take a static distance observed in one frame, and then added a dynamic element to it (my MOVING twin). And then came up with a mathematical equation to balance both frames of reference so they're valid, to both observers. It's apples and oranges. Yes, the math works, and SR explains the observer dependant nature of the universe. But, in reality, does my twin really come back younger. And again, as I stated earlier, if you use some of the math, you have to use it all. Does he comes back exponentially heavier and exponentially thinner!?

    7. #32
      Xei
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      This has already been covered. You're just going in circles and ignoring things you don't want to hear. The speed of light has been measured in different frames, not just one, and found to be constant. The results of these experiments were very surprising and motivated special relativity in the first place. Experiments have also been done to measure the time dilation effect which occurs in the twin paradox. Time dilation did occur in these experiments, to the exact degree which relativity predicts. You're at perfect liberty to deny that these experiments took place, but they did, and that's that.
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