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location Berlin, Germany
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visits member for 1 year, 4 months
seen Jun 4 at 21:17

Dec
5
comment How is it possible for astronomers to see something 13B light years away?
So my error lies in the (maybe naïve) assumption that being x ly away from the incident means that I will "see" it in x years? If that assumption is wrong, what the heck does ly mean then? What about the constancy of speed of light? Doesn't that shatter everything? What about today? Is that "feature" still valid, so meaning that an event on the Moon (≈ 1ls away) will be "seen" by an observer on Earth not in 1s but in slightly more time?
Dec
5
comment How is it possible for astronomers to see something 13B light years away?
Yeah, that's the same you said in your original answer. But what I'm wondering about is that this seemingly contradicts GR in that aspect that each observer is validly allowed to explain things from his point. The expanding of the universe (AFAI understand this) should be explained by that "feature" of GR, not being an add-on to GR. Still, I'm sure you are right, but I don't understand how to solve that contradiction.
Dec
5
comment Why can we see the cosmic microwave background (CMB)?
That's not explaining why we still can see it. If the CMB was emitted in a universe of age 380ky, then that universe cannot have been very large, say, at most twice that size in diameter (760kly). According to GR each observer can be taken as a point of reference and for each is valid that he should have seen the last of that CMB at most 760ky after that event. Where's my mistake?
Dec
5
comment How is it possible for astronomers to see something 13B light years away?
This "expanding of the universe" thing is kinda weird for me yet. Doesn't GR state primarily that one can take any observer and explain all surrounding events from his point of reference? If so, I'd like to take "Earth" of the time of the GRB (yeah, it wasn't there yet, but let's assume to simplify things) as my point of reference, then the GRB happened in x ly distance, so it should have arrived after x years, according to GR, no matter how things moved in the meantime. But if the universe was only 1 billion years old then, x could only be 1 billion at most. Where's my mistake?
Oct
21
comment Time dilation only on electromagnetic force?
Right, Nicolas. Stupid me. I could have thought of them myself.
Oct
21
awarded  Student
Oct
21
comment Time dilation only on electromagnetic force?
@Nicolas, yes, we receive radiation on the surface of the earth which is composed of particles which should not have survived through their voyage due to them being very short-lived (when stationary). The explanation for this is that they experience time dilation, so I guess that counts as a "clock" based on decaying particles (I'm not sure whether strong or weak force is their incentive, though). Stays the question about gravitation; do we have clocks based solely on that? (I. e. without using the other forces as well as pendulum clocks do.)
Oct
21
comment Time dilation only on electromagnetic force?
So I take it that there also have aspects been found which indicate that also the gravitation's speed is depending on c? Feynman's quote is a nice way to put the thought. Are there mathematical or otherwise computational ways of handling things which use this different view? Or is the difference too academic to be pragmatic?
Oct
21
asked Time dilation only on electromagnetic force?
Mar
27
awarded  Supporter