Red Shift

[Purves Grundy]

A dumbo's science question prompted by tonight's Horizon (which is basically just another re-heat of about 5 or 6 other identical "Waiting for the GUT" editions).

Beyond Red Shift what other experimental/observational evidence is there for the galaxies moving away from each other?

[Andy C]

Red Shift

I rather relished the conclusion to the effect that more knowledge of black holes could enable us to predict the mechanisms of the origin of the universe.

[hobbes]

Red Shift

Red shift's pretty much it, PG.

[Purves Grundy]

Red Shift

That's what I thought. Well, seeing as all intergalactic light will be subject to red shift (and I think I'm correct that the further away a galaxy the redder shifted it is) has the possibility been embraced that perhaps there's something else going on?

I mean, maybe there's something about travelling the vast intergalactic distances that in some way fucks up light's shit and makes it shift to red.

Because isn't it the assumption that the Universe is expanding that means they have to cook up theories like dark matter to plug the gaps such as there not being enough matter for gravity to work in an expanding universe.

[Wyatt Earp]

Red Shift

There's clearly something other than distance involved, though, because the correlation between distance and red shift isn't perfect.

And the thing is, the behaviour of waves, even at light-speed, is so well understood, so "core" to physics, that it would be massively more bizarre if some hitherto unknown "spatial effect" on frequency were to emerge than if there were just a whole load of matter we can't see. As bizarre as that is, it's way less bizarre than the idea that we might have got the relativistic Doppler effect wrong.

[Wyatt Earp]

Red Shift

Not a bad Horizon, that, was it? A lot of it was old hat, but then a lot of science is old hat. The physics programmes seem to have reversed the dumbing down a bit. There were even equations.

I've sort of met Michio Kaku--I introduced a talk of his once to schoolkids--but we didn't have a conversation so I'm not counting him on that other thread.

[Andy C]

Red Shift

No, you're right, it was pretty good. Represented the knowledge domain pretty fairly given the restrictions of a single television programme, and put together well enough to kepp the interest of the reasonably informed layperson.

[Guest]

Red Shift

Redshift freaks me out. Because when we talk about it we are talking in terms of the bit of the spectrum we can see. Like, what if we could see infrared or microwaves or whatever. And so it reminds me of how our biology determines how se see/perceive/experience/describe/discuss everything. How would we feel about eg redshift if we saw differently? So the bit I can't handle is that, OK, we're describing an effect on our perception of waves caused by the relative distances between us and what's peceived. if i've understood it, physics GCSE was a while ago now. And we have two levels of relative. The one that is our changing distance from the observed thing and the other is the mediation of our physical selves, eyes etc, between us and the observable world. And I can't help it but it makes my head spin. And without us here to observe it, redshift would be meaningless/indescribable??

[Andy C]

Red Shift

we're describing an effect on our perception of waves caused by the relative distances between us and what's peceived

No, this isn't correct in two ways. Firstly, it's an effect caused by the relative velocity of the two objects (the source of the waves and the observer), not the distance. And secondly, it isn't an effect of perception like some optical illusion (if I'm correct in my interpretation of the phrase "mediation of our physical selves"); it's a real, measurable change to the waves themselves. The name "red shift" seems, unfortunately, to be suggesting to you that it's an effect confined to the visible part of the spectrum, but that isn't the case. Waves of all frequencies are affected in exactly the same way by the relative motion of source and observer.

[Disco Child Ballads]

Red Shift

My Dad's met Michio Kaku as well. I'm afraid that's all I can contribute to this dicussion, but I do find all this sort of stuff absolutely fascinating.

[Ginger Yellow]

Red Shift

Because isn't it the assumption that the Universe is expanding that means they have to cook up theories like dark matter to plug the gaps such as there not being enough matter for gravity to work in an expanding universe.

Technically, dark matter was originally hypothesised to account for the fact that observable matter wasn't sufficient to account for the rotation speed of some galaxies. It's since (mainly in the last five years or so) been backed up by a lot of other observations. It's dark energy that is supposed to account for the expansion of the universe. It also, rather neatly, stands in for the cosmological constant which Einstein originally had in his equations for general relativity.

[Guest]

Red Shift

Thank you Andy. Yes I understand that it's measurable and happens with waves of all frequencies - that's why I said if we could see infrared, etc. Although if we could see infrared etc, red shift would be shifting away from red, not towards it, if I'm right? That's sort of what I meant. It's real and measurable and would happen if there was no one on earth (or anywhere) at all. (I assume it would happen if an observer were elsewhere in the universe?) But we only know about it because we're able to look for it. I'm not saying this is unique to redshift, not at all, just that the way we describe redshift particularly reminds me of how our science is often only about what it's possible for us to observe rather than some kind of Godlike exterior truth. There's exterior truths there, maybe, but I as a non scientist am just baffled by how our relationship with them works.

Thanks for the correction about velocity - of course, it wouldn't make sense otherwise. I did vaguely know that somewhere but like I say, gcse physics...

[San Bernardhinault]

Red Shift

Red shift is, at best, a good approximator for distance. On the assumption that the universe is expanding, because most galaxies are red-shifted (only most, though, there are a few blue-shifted ones), you can say that the level of red-shift is a first approximation link to the distance of a galaxy from us.

If you then plot galaxies by their red shift, though, you get some very interesting artefacts, best of which are the "Fingers of god" - which are lines of galaxies which point straight at us, in the centre.

What these are, though, are galactic clusters - and because in each cluster the galaxies have their own speed relative to each other (or to the centre of the cluster), the red-shift changes and is inconsistent for each element in the cluster. Which means that the cluster appears to get spread out along the distance axis, although we know, fairly accurately, the radial position.

Although it's indicative of a large statistical error in the observation of distance using the redshift, it actually is a very good indicator that red-shift is a real thing.

[Wyatt Earp]

Red Shift

Lyra, I must admit I'm baffled a bit; not being smartarse, I promise. Is what you're saying something to do with the use of the word "red"? Because that's there for parochial reasons, yeah, having to do with the fact that the effect was first observed in the visible spectrum. But I mean, it just happens to be the word we use. "Red" here is just standing in for "lower frequency, longer wavelength". We could call it "long shift" or "radio shift" or something, and it would still be the same, objective, universal phenomenon. Reflecting an exterior truth (though I'm not comfortable with "Godlike", surprise surprise).

The really weird "what is truth man?" stuff is quantum mechanics, and in particular Bell's theorem on the nonexistence of local hidden variables (or, to put it another way, the nonexistence of "exterior truths" as we understand them at the classical level).

[Guest]

Red Shift

No, it's not just about red. I'm just being thick. I am trying to explain why it feels freaky but am too thick to say it properly. What was that thing on that other thread about humanities people being unable to express themselves? That's me.