Re: How can light travel without losing energy?

Nick Maclaren wrote:
In article <dfjs6n$jv4$1@xxxxxxxxxxxxx>,
Einar Andreas R鷣land?= <e.a.rodland@xxxxxxxxxxxxxx> writes:
|> |> "Tired light", ...
|> |> The explanation from someone better qualified than me:
|> http://www.astro.ucla.edu/~wright/tiredlit.htm

Interesting, but not quite as conclusive as it implies.  In a
few places, it debunks some of the less plausible variants of
tired light theories, and implies that the conclusions apply
to all of them.  For example, the speculation I threw in the
air is NOT incompatible with the CMB spectrum data (though, until
and unless someone produces a real theory, it isn't compatible
with it, either) - it is just a place-holder.


I'm no expert, but from what I tell this is not correct.

The suggestion you put forward, that light might interact with something producing more photons but with less energy each, would cause the light to be spread so we would see distant objects as blurred at best. Secondly, your suggesting would have increased the number of photons; "classical" tired light models retain the number of photons; in reality, the density is reduced as illustrated in the link I gave.

However, no matter what, any theory or model can be argued to be possible. Even the circle-within-circle model for explaining planetary motion is possible in the strict sense of the world: it's just that it was a total failure as a scientific theory.

I guess you can say that the central dogma in natural sciences is the idea that there are laws of nature---absolute, empirical or probabilistic---that allow us to explain/describe nature around us effectively; and that if a small set of assumptions enables us to explain a large set of phenomena, then those assumptions are likely to be closely related or similar to how nature actually works and thus allow us to generalise (induce) from what we have observed to what we have yet to observe.

Thus, when one small assumption---that distant objects are receeding from us---is able to explain a large number of observations without having to rewrite known laws, it seems like a good explanation: it is one that is likely be enable us to generalise and make predictions.

When an assumption (tired light) that requires that some fundamental laws need to be rewritten (conservation of energy-momentum) in order to explain *one* observation, and then a new assumption for every new class of observations, there is no reason to expect this set of assumptions to tell us anything about the next thing we're going to observe. It's the circles-within-circles: every new or more detailed observation requires an additional set of circles to be added to the model.

But can anyone provide any REAL evidence that physical constants
have been EXACTLY the same as they were shortly after the big
bang?

In what sense is there any "REAL evidence" that the motions of the planets is not governed by circles-within-circles?

Given that the number of unknown factors that have been invented
to account for anomalous observations ("dark matter", anyone?),
it seems a little biassed to state that an out-of-favour theory
is impossible on the basis of assuming a couple.

Any description of nature is likely to break down when you push it far enough. With the Big Bang theory, you have to push it quite far; with tired light, you don't even have to start pushing.

Secondly, the problem with the "dark matter contradicts Big Bang" argument is simply that at the level of galaxies and clusters, the motions observed do not contradict the Big Bang theory, but ordinary laws of physics: Newtonian gravitation. Judging by the motion of the bodies we can see, there must be more matter there than we can see. Now, that's roughly the argument that was used to deduce that there has to be another planet (Neptune if my memory serves me right) in the solar system; and fortunately they tried to find it rather than just conclude that Newton had to be wrong.

Where there is an interaction between Big Bang and dark matter is that the Big Bang theory also tells us a lot about the expansion of the universe, and this again tells us something about the amount of mass and energy in it. Again, you have to push the theory very far indeed before real problems start to arise. And since the dark matter hypothesis is needed also at the level of galaxis and clusters, independent of Big Bang, there should be no shock this should have some effect at the universal level.

Tired light, however, doesn't even get to this stage. And the dark matter problem of galaxies and clusters would still have to be solved. Thus, tired light is as dead as a scientific theory as the good old circles-within-circles theory. It was worth looking into to see if there might be something there...but there wasn't.

Einar

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