Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Fluid_thinker on 14/05/2009 12:58:38

Many equations require the creation of an average value (due to the inherent difficulties of some problems, e.g. average matter distribution).
We then try to solve problems like understanding the expansion rate of the universe, which leads to something we do not understand or have much idea about e.g. Dark Energy
What is the effect of this avergaing? Does the potential error rate get anywhere near impacting these ideas?

When thinking of problems like the expanding universe, it makes more sense to me to dig into why exactly is it that we sense an expanding universe? A lot of times when nature seems to misbehave, it is due to some wrong assumptions we have made about nature. In the past we assumed that earth was at the centre of the universe. Nature seemed to misbehave.
I suspect we have made some wrong assumptions and are now trying to force nature to comply with our assumptions. For example, we first assumed the red shift in the stellar spectrum was a Doppler effect. Then we noticed that nature must be misbehaving. We saw that matter needed to move faster than the speed of light to get to its present state. Now we assume the shift is due to expansion and that the expansion stretches the light, no longer restricting it to a speed of c.
Maybe the second assumption in the last paragraph needs work. [:)]

Good question: What sort of 'average' is used?
Is it the arithmetic mean, the median, the mode, the harmonic mean, the geometric mean? I guess, if they are looking at stars which are all the same sort of distance away and 'averaging' their recession speeds, then the arithmetic mean would be appropriate as long as the spread is not too great with respect to any nonlinearity that may arise when the distances are great. Average density would possibly need to include some consideration of time of observation as a consequence of distance (because of finite light speed and expansion).
A lot of statements made abut the Universe seem to imply that an observer is outside looking in and that everything is happening at the same time. Whereas, in fact, the impact (strength and timing) of what happens in one place is affected by the distance away of the phenomenon 'when' it happened.
Verne; the idea of stretching avoids the problem of exceeding c, doesn't it? Metres per second is still the same it's just that the metres may have changed.??

Verne; the idea of stretching avoids the problem of exceeding c, doesn't it? Metres per second is still the same it's just that the metres may have changed.??
Exactly; that was my point. [:)] We made an assumption that modified natures behaviour. It solved a difficult problem. But the assumption is not testable beyond its ability to solve the present problem.

We're back to my difficulty with the "what's really happening?" type of question. They are all just models of reality, as we see it. If the model works and is consistent then I don't think we can ask much more of it. When another model comes along which includes all the present phenomena  plus a few new ones  we can use it. But we may not be able to reconcile our present model with the new phenomena.

We're back to my difficulty with the "what's really happening?" type of question. They are all just models of reality, as we see it. If the model works and is consistent then I don't think we can ask much more of it. When another model comes along which includes all the present phenomena  plus a few new ones  we can use it. But we may not be able to reconcile our present model with the new phenomena.
This is very true and I agree. My only worry is that we may be too ready to dispose of the rules of nature when they contradict our assumptions. What if it is true that Lorentz was correct about spacetime? Every established theory that needs spacetime as a variable would have to be rethought.

The expansion of the universe is ONLY observed as an average rate over very large distances. The "random" motions of galaxies prevent small measurements over shorter distances. It would be quite possible for this expansion to be quite variable locally, say for example dependant on the density of matter or dark matter and that variation not to be observable. As far as I know there is no way this expansion could be measured or detected over small human controllable scales although the actual expansion over this scale is in theory within the limits of measurement. Gravity wave measuring devices are looking for much smaller changes in long distances over time.

Picking up on the variable expansion possibility. In the 'VOIDS' that have been found. It is possible to compare the results of the expansion in a Void versus the expansion of a heavily dense area of galaxy/matter. Surely there must be a variance, as there is less gravity.
We appear to be discovering more and more of these voids, of which some are massive. Does this not have an effect on Expansion?