socrat44 wrote: ↑Sat Feb 23, 2019 8:59 am
@Scott Mayers
one thought experiments :
you are swimming in a smock ocean and no
''matter-like or energy-like'' around you:
do you really swimming or it is only your dream ?
can you swim independently ?
P.S.
Light can ''swim'' independently.
Second Postulate of Special Relativity
The speed of light c is a constant,
and independent of the relative motion of the source.
========
Your translated English is hard to follow. But it sounds like a type of thought experiment Einstein did imagine. If you pretend that you are the only thing in the Universe, you have nothing to compare any 'speed' to. One can extend this to having two people. Using two skaters, for instance, might question if they are spinning with respect to each other. Can you infer they are 'spinning' or not? One proposal is to say you can if they are fully extended away from each other similar to the effects of a centrifuge.
Replace the people with imaginary masses and some string connecting the two. If they do not come together as we expect is natural for masses with gravity to do, if the string remains taught with the masses not coming together, it might suggest spinning is occurring. ....But spinning relative to what, if not some background?
We cannot seem to answer this except to realize that for such to be realized true, an imaginary 'observer' is needed as a third independent thing/mass in this space. So, if 'space' is itself not something itself we can observe directly, then 'speed' is determined as referent changes with respect to other masses. A third mass is thus needed (as a relative 'observer') to notice the two other objects change with respect to each other. IF all mass is not created nor destroyed, AND this implied that all masses are on par with each other as equivalent references relative to one another, then the 'limit' of speed is only defined by the relative factors that make them move with respect to one another, not to some needed background.
For example, let us now imagine then that we are in an ideal spaceship in which we can use any atom's energy it contains in both traditional 'fuel' AND the very components of the ship to accelerate with respect to some original platform we take off from. An ideal third 'observer' is what acts to 'measure' the relative distance of change in space when the craft first leaves that platform. It doesn't matter how fast that frame of reference is with respect to anything else.
When we burn fuel, it basically requires losing mass to the spacecraft to accelerate. Since we imagine we can use all the atoms of the craft to be fuel, the more we accelerate, the more mass we require to lose in order to get faster. But since the space ship is 'finite', then we are limited to accelerate no faster than the fixed quantity of atoms of the craft. Thus, ....for any fixed mass, there is only a fixed maximum speed that anything can be accelerated to because it loses mass used as fuel until it has no mass at all.
This 'proves' in a thought experiment how and why a fixed speed is required about anything observable in space, which includes that which we use to interpret something sensed most remotely, such as light. Therefore, light, being the phenomena we perceive observations fastest with is also our means to map the fastest speed limit to.