5 ms·

"size differences are illusory" So two things standing next to each other are the same size as one thing alone? Damn hard to imagine. I would think "size" doe

by itry 12y ago

"size differences are illusory" So two things standing next to each other are the same size as one thing alone? Damn hard to imagine. I would think "size" does not really "exist" but is a man made concept. And by its definition, two things next to each other form a "bigger" thing.

coldtea 12y ago
The article is badly written, but it doesn't really mean sizes are illusory (even if it says so at the beginning). It goes on to say that sizes and mass "spontaneously emerge" from lower interactions, which is to say, they become real for us. But, to address your example: "So two things standing next to each other are the same size as one thing alone? Damn hard to imagine". That might not hold for size, but a very similar thing does occur (and is proven) for speed. If you are in a car that goes at 0.8 miles per minute, and you throw a dart that goes at 0.3 miles/minute, its speed is 1.1 miles/minute (the sum). But if you travel at the 0.8x the speed of light and you throw something forward at 0.3x the speed of light, its speed is not 1.1x the speed of light, but c. That is, trying to add velocity doesn't get you faster than the speed of light. http://curious.astro.cornell.edu/question.php?number=145 http://curious.astro.cornell.edu/question.php?number=145
- lutusp 12y ago
  > But if you travel at the 0.8x the speed of light and you throw something forward at 0.3x the speed of light, its speed is not 1.1x the speed of light, but c. Not really. Velocities near c don't sum that way. And your reference doesn't support your claim.
  - gus_massa 12y ago
    I agree. More details: http://en.wikipedia.org/wiki/Velocity-addition_formula http://en.wikipedia.org/wiki/Velocity-addition_formula If you add two velocities that are less than c, you can never get c, you always get something smaller. 0.8c + 0.3 c ~= 0.887 c (It's smaller than c) At low speeds the effect still exists, but it's negligible. There is an important difference between "it doesn't exist" and "it's so small that if we forget it we will be fine". It's so small that you must use floating point numbers with too many digits to calculate it. It's more useful to calculate the difference between the "relativistic" sum and the "classical" sum. Another way is to aproximate the formula with a Taylor expansion dif = (X+Y) / (1+(X * Y/c^2)) - (X+Y) ~= - (X + Y) (X * Y/c^2) 0.8mph + 0.3 mph = 11mph - 5.9 * 10^-39 mph The correction is veeeeery small.
    - lutusp 12y ago
      > The correction is veeeeery small. Indeed it is. The only place I can think where such a small correction matters is in the GPS system. The accuracy of the GPS system depends on tracking down and eliminating every possible source of error, and to maximize position accuracy, two relativistic effects are accounted for: 1. The time dilation caused by the satellites' velocity, from Special Relativity. 2. The rate of time passage at orbital altitude compared to that at the surface, which reflects the gravitational well effect of General Relativity. The two effects move in opposite directions, but they don't cancel out. The applied correction (to the orbiting clocks) is very small indeed, but enough to avoid a gradual but serious decline in positional accuracy over time.
      - xrange 12y ago
        Does anyone know of a general & special relativity simulator? That is, a program where I can setup various "thought experiments", by placing clocks and masses at various point in space, where they can have various acceleration profiles, and can communicate with each other, and run the scenarios? I never really understood the twins "paradox" and the explanations for the source of the asymmetry seemed hand-wavy and "because".

by itry 12y ago

coldtea 12y ago

The article is badly written, but it doesn't really mean sizes are illusory (even if it says so at the beginning). It goes on to say that sizes and mass "spontaneously emerge" from lower interactions, which is to say, they become real for us. But, to address your example: "So two things standing next to each other are the same size as one thing alone? Damn hard to imagine". That might not hold for size, but a very similar thing does occur (and is proven) for speed. If you are in a car that goes at 0.8 miles per minute, and you throw a dart that goes at 0.3 miles/minute, its speed is 1.1 miles/minute (the sum). But if you travel at the 0.8x the speed of light and you throw something forward at 0.3x the speed of light, its speed is not 1.1x the speed of light, but c. That is, trying to add velocity doesn't get you faster than the speed of light. http://curious.astro.cornell.edu/question.php?number=145 http://curious.astro.cornell.edu/question.php?number=145

lutusp 12y ago
> But if you travel at the 0.8x the speed of light and you throw something forward at 0.3x the speed of light, its speed is not 1.1x the speed of light, but c. Not really. Velocities near c don't sum that way. And your reference doesn't support your claim.
- gus_massa 12y ago
  I agree. More details: http://en.wikipedia.org/wiki/Velocity-addition_formula http://en.wikipedia.org/wiki/Velocity-addition_formula If you add two velocities that are less than c, you can never get c, you always get something smaller. 0.8c + 0.3 c ~= 0.887 c (It's smaller than c) At low speeds the effect still exists, but it's negligible. There is an important difference between "it doesn't exist" and "it's so small that if we forget it we will be fine". It's so small that you must use floating point numbers with too many digits to calculate it. It's more useful to calculate the difference between the "relativistic" sum and the "classical" sum. Another way is to aproximate the formula with a Taylor expansion dif = (X+Y) / (1+(X * Y/c^2)) - (X+Y) ~= - (X + Y) (X * Y/c^2) 0.8mph + 0.3 mph = 11mph - 5.9 * 10^-39 mph The correction is veeeeery small.
  - lutusp 12y ago
    > The correction is veeeeery small. Indeed it is. The only place I can think where such a small correction matters is in the GPS system. The accuracy of the GPS system depends on tracking down and eliminating every possible source of error, and to maximize position accuracy, two relativistic effects are accounted for: 1. The time dilation caused by the satellites' velocity, from Special Relativity. 2. The rate of time passage at orbital altitude compared to that at the surface, which reflects the gravitational well effect of General Relativity. The two effects move in opposite directions, but they don't cancel out. The applied correction (to the orbiting clocks) is very small indeed, but enough to avoid a gradual but serious decline in positional accuracy over time.
    - xrange 12y ago
      Does anyone know of a general & special relativity simulator? That is, a program where I can setup various "thought experiments", by placing clocks and masses at various point in space, where they can have various acceleration profiles, and can communicate with each other, and run the scenarios? I never really understood the twins "paradox" and the explanations for the source of the asymmetry seemed hand-wavy and "because".