Re: Relativistic aberration

On Thu, 18 Jul 2024 6:33:27 +0000, Thomas Heger wrote:

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Am Mittwoch000017, 17.07.2024 um 14:05 schrieb gharnagel:

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On Wed, 17 Jul 2024 7:05:15 +0000, Thomas Heger wrote:

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What we see in the night sky is actually our own past light-cone.

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Ah, but if we can develop tachyon astronomy, that will not be true!

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Well, if light would speed up somehow in remote corners of the universe,
we would still see what we see in the night sky, if this phenomenon
would not change in observable timespans.
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Possibly there are tachyons, but those are invisible anyhow, because we
can see only light and light moves with light speed and tachyons don't.

"See" is an interesting verb and "light" is an interesting noun.  We use
them to describe situations where we don't actually use the band between
0.7 and 0.4 um.  We now can "see" gravitational waves and interstellar
neutrinos, as well as IR and UV astronomy thanks to scientific advances.
PTOLEMY may expand the field to "relic" neutrinos (which may be
tachyonic).

This means: light is relatively slow for the wastness of the

universe,

hence we can see everything only with a certain delay and the

further

away, the longer the delay, according to x = c* t
(with x= distance in meters, t = delay in seconds).
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This 'longer away' is usually measured in light years and the delay

in

years.
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Since the night sky shows only a delayed image of past events, the

speed

of light cancels out of the equations and we can put any value into

it

and always get a valid picture of the universe.
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So we only assume, that light moves always with ~300 million meters

per

second through the entire universe.
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But if light would speed up or slow down, we would not be able to
measure this, because we always see the own light cone in the night

sky

and c is already embedded into it (for whatever a value c actually

has

in outer space).
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TH

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Ah, but the fine structure constant, which is pertinent to how stars
shine, includes the speed of light.  That implies that c is the same
throughout space and time, n'est-ce pas?

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Well possibly.
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What I wanted to say is this:
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what we see in the night sky is light, that stems from remote places in
the universe.
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Since light is very fast, but space is also very large, we have a
significant delay for the travel from such remote place to us observers.
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This makes the image we see a little unreal, because it is not only old,
but also 'layered in time'.
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To untangle this picture and create kind of realistic picture of the
universe, we would need the distance to those remote places.
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Since we only have light to see, we can assume c=~ 300 million meters/s
as light speed.

Some assumptions stand on much better foundations than others.

But what if that is not always the case???
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Could we somehow find out??
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No, since c is already used to determine the distance to these events.
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If now c alters mysteriously along the path, we had to determine the
distance by other means (which we do not have), hence cannot measure,
whether or not c stays always the same.
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TH

It's always a good idea to check one's tools to make sure they work in
new domains.  The fine structure constant may not be the only check we
have on c though.  Can you think of others?