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[Sean Mirrsen]

My complaint is that the movement-away is attributed to space stretching. And partially that gravity is (as a secondary effect) stretching space, which makes about as much sense as aether to me.

You see, until you shove an unbendable rod of sufficient length alongside the sun and see that it's not straight, it's not a defining experiment. The path of a physical object around the sun would curve in roughly the same fashion as the light's path would. And remember, light has no mass only in relativity et al. Mass is energy - if you have energy, you have mass. Whether it's rest mass or velocity mass, or whatever name you come up with for it, nomenclature doesn't matter, pun not intended. The light's trajectory as a non-relativistic occurence could be explained in a simple way, even if math for it doesn't line up well.

[Flaede]

My complaint is that the movement-away is attributed to space stretching. And partially that gravity is (as a secondary effect) stretching space, which makes about as much sense as aether to me.

You see, until you shove an unbendable rod of sufficient length alongside the sun and see that it's not straight, it's not a defining experiment. The path of a physical object around the sun would curve in roughly the same fashion as the light's path would. And remember, light has no mass only in relativity et al. Mass is energy - if you have energy, you have mass. Whether it's rest mass or velocity mass, or whatever name you come up with for it, nomenclature doesn't matter, pun not intended. The light's trajectory as a non-relativistic occurence could be explained in a simple way, even if math for it doesn't line up well.

I think for most of us here, if the math doesn't line up well then the explanation is not really a workable one. If your explanation results in 2+2 being 1, for instance, then our universe is not running by those rules (unless I missed some interesting mathematical trick).

From what I understand, no matter what theory you subscribe to, gravity pulls stuff together, but has an observed "range of effect" (not sure the right term there). Setting aside the argument on light having mass, everything (of a certain mass) is moving away from everything else (that is farther away than said mass' gravity affects strongly), any theory of the nature of space and whatnot has to resolve with "the math" created by these measurable observations.

Now I'm wondering: why do physicists assume that the large masses of the universe are moving away from each other? Could it not just be that everything in this "gravity warped space" is simply sinking deeper - ie. all getting more compacted/closer together? Is it just that the two are functionally equivalent (look/act exactly the same), or does the assumed direction of 'movement' have something more behind it? Like ferinstance that the observed changing light wavelengths only work with the one case and not the other?

[Neruz]

The way we worked out that the other galaxies are all moving away from us is because the light coming from them is red shifted. Amongst other things.

Wikipedia (as always) has moar.

[Sean Mirrsen]

Actually, 2+2 being something else is the brilliant work of the rule of exceptions. The rule states (in my edition) that "Any rule or set of rules may have at least one set of circumstances in which the rule does not hold, provided the circumstances are specific enough. The same is true for the Rule of Exceptions itself." What it means, is that if you take 2+2 without specifying that these are, in fact, real decimal numbers you're counting, you can end up with 1 or 3 or 6 as well as 4. (adding 2 liters of water to 2 liters of alcohol, for instance, makes less than 4 liters) If you begin specifying details, at some point the Rule will dismiss itself - a sufficiently specific set of rules is an exception to the rule of exceptions.

What we have in the world are insufficiently specific rules and laws, and fairly specifically done experiments. Lasers or particle accelerators don't frequently occur in the universe by themselves, and experiment results with them involved could possibly fall victim to the Rule.

ninja-reply-edit: So wait, red-shifting light is a sign of the galaxies moving away, and red-shifting background radiation is a sign of the space expanding? Double standards again? Ever occured to anyone that background radiation could be, say, light reflected from the opposite side of the expanding universe that's been redshifted into nothingness?

[Il Palazzo]

The way we worked out that the other galaxies are all moving away from us is because the light coming from them is red shifted. Amongst other things.

Wikipedia (as always) has moar.

I think that Flaede asked if there is any definite reason for favouring the "space expands, while locally gravity prevents it's expansion" over "space does not expand, but locally gravitation makes it shrink", which would, at least at a first glance, produce the same observational results. I.e. the expanding universe.

[Starver]

If i wrapped a fiber optic cable around the earth X amount of times and then shown a light in one end, the light coming out of the other end would be delayed if it went around enough times, right?

You do know that it would be delayed even if it was a metre length of cable.  A millimetre.  Shorter, if you could arrange that.  Of course, it would be a small delay.  I hope you're not asking this question based on questions of relativity/rapidly moving light around, because 'classical' interpretations of light-going-the-speed-of-light apply (almost[1]) the same.

So what would happen if i connected one end to the other?

Ninjaed, but it reminds me of a time when I was very young I was convinced that if you got an electrical extension, plugged in the plug to 'charge' it with power and then quickly (very!) unplugged from the socket and into itself (like the self-swallowing snake) you could carry around power from one place to another.  Of course, that wouldn't work for so many reasons unrelated to the optical cable one (like the fact that it's an AC oscilation, etc) as well as the whole losing effectiveness through resistance/opacity one.

Actually, though just like a rotating electrical charge must produce lose energy through synchrotron radiation, I suppose there's some loss of power in an optical cable in a circuit, of some kind, over and above the normal loss of power in an equivalent length of straight cable with perfectly-aimed photons heading down the centre of it.  Mechanical force?  I suppose that depends on how you abstract the quantum interaction of light through the given medium.


[1] Effects of being in a gravity well, etc, aside.

[Starver]

Maybe just the universe is? If the fabric of space was expanding, then it'd affect the entirety of matter, not just distant galaxies. The moon would move away from Earth, the Earth would move away from the sun, your left foot would move away from your head. Except every ruler and distance measuring device would tell you nothing is happening. Because if it's an expansion of space, all possible measuring devices will expand with it.

There's theories (with some support) that expansion in the ever aging universe can increasingly outstrip the observational horizon.  Light from the furthest galaxies that we can see will no longer (after corresponding time has passed for 'us' now and 'them', way back when) the space will have expanded so that the later light never does reach us.  And then after more time (and we're talking a lot of time, many billions of years, IIRC) even less distant light-sources will be spewing photons that will never reach us.  This would not be noticed on more local levels (except by observant sky-watchers) in any real sense, due to the proportion of expansion being insignificant on microscopic, macroscopic or even galactic distances.

But wait long enough, and even the local group of galaxies will be 'beyond' the observable limit of the universe.  And then parts of our galaxy, and then most of it, and eventually nearby stars, then all stars, then the limit will be within the limits of the (long-extinct by then anyway) solar system, and so on until the last remaining atoms are effectively 'ripped apart', having long since lost contact with any more siginificant amount of matter that might have been allowed clumping together as planets, moons, asteroids, space-craft, living beings and even molecules.

Just a theory, but based upon the expansion of the fabric of space.

It may or may not directly relate to the above, but as an example, the current observable universe is supposed to be a bit less than 50 billion[1] light years distant (although the light has been travelling only 13 or so billion years).  Get an elastic band that long, anchor it at a point at the edge and wait another billion years and you'll get a slightly stretched band.  Very slightly.  But add another billion light years (it'll probably be more) and your elastic band is only about 2% longer (ignoring other effects and assuming constancy of expansion).  Every year it stretches 0.000000002%  Mark out a metre length now, and in a year's time you'd have (unless I've gotten a power of ten or two wrong, in my head) 20 picometres extra distance.  The diamater of a Helium atom is supposed to be 60 picometres.  The Carbon-Carbon bond is 120-150 picometres, IIRC.  So even if it was a monomolecular carbon thread instead of an elastic band, and all the expansion in any given metre were concentrated between one particular pair of atoms, it might not elicit a break.  But as it's distributed between all the many bonds it certainly wouldn't.  Even a millenia of stretching wouldn't break a -C-C-C-C-C- chain (or a =C=C=C=C=C= one, if you want it purer) otherwise protected monofibre.

And the Moon is moving away from the Earth.  But far quicker, and that mainly due to more mundane reasons regarding transfer of orbital and rotational energies between various bodies.  And during puberty, your left foot (ignoring the transient effects of locomotion itself) is probably travelling faster away from your head than the Moon is the Earth.  And while physical rulers would expand accordingly with the expansion the universe, signal-based ones (the time taken for light to travel) would reveal some expansion.  (Actually, physical ones would, as well, by observation of the ends by an external observer, but that's complicated and really needs explaining.)


[1] Am assuming that's the US billion of 10^9, rather than the UK one of 10^12, in all my calculations.

[Sean Mirrsen]

What I find wrong about the expansion of space is that it implies matter as something that's somehow rooted to the fabric of space-time, while energy is 'free-floating' and unaffected. In actuality, all energy constructs such as waves or photons would be affected just as well as matter because the two are inseparable. Space exerts no force. If it expands or warps, it isn't pulling things apart, it simply makes them arbitrarily larger. Energy bonds won't break because for the energy, the distance remains the same.

Btw, something I thought of. With gravity redshifting light, doesn't it mean our sun is actually green? Or at least greener than we see it.

[dreiche2]

In a word; no. That's not what is happening at all. What is happening is the space around the start is being warped. The light is travelling in a perfectly straight line, it's just that around massive objects, straight lines aren't so straight anymore.

Gravity can't affect light directly; light has no mass remember?

No, that's actually not true. Light just doesn't have any rest mass, but it does have mass (as anything), and it is being affected by gravity "directly". The warping of space is how gravity affects anything.

And to Sean: You don't really care about science, do you? Just because something is or isn't intuitive to you doesn't mean it's true or not. You claim theories are wrong while not really understanding them, you ignore evidence, you imply you're smarter than thousands of scientists, and you don't have a consistent or quantitative theory for an alternative either (you didn't get back to me on that moving laser problem btw).

What you should do is study some maths, at uni. Because maths has loads of intuition breaking insights as well, and unlike any other field, you can actually prove things, so there is no discussion any more at some point. Personally, I learned a lot about how one's intuition can be foolish by doing maths at uni. Coming up with a theory of the universe solely based on intuitions is ludicrous.

Late edit: I apologize if this sounded a little bit harsh, I'm not sure how it comes across. I just got annoyed by you constantly calling well established theories ridiculous, but I don't want to argue.

[Starver]

What I find wrong about the expansion of space is that it implies matter as something that's somehow rooted to the fabric of space-time, while energy is 'free-floating' and unaffected. In actuality, all energy constructs such as waves or photons would be affected just as well as matter because the two are inseparable. Space exerts no force. If it expands or warps, it isn't pulling things apart, it simply makes them arbitrarily larger. Energy bonds won't break because for the energy, the distance remains the same.

I wrote three (long) paragraphs of explanation, but I'm doing too much writing.  I'm sure someone else can do it in less words than I.

Btw, something I thought of. With gravity redshifting light, doesn't it mean our sun is actually green? Or at least greener than we see it.

Bluer.  The opposite of Red is Blue, in official terms.  Green is opposite Red on the pigementation "colour wheel" (and cyan on the additive 'light' version) but Blue (actually Violet, but close enough) is at the far end of the linear spectrum from the Red one, and thus "Blue-shift" is the term used for the doppler effect applied to rapidly approaching (or similarly distorted) light emiters.

Except that any shift we see on the Sun is insignificant, either way.  Our gravity well is too puny to make a visible differerence to the spectrum (ignoring the atmospheric filtering effects).  It's in light from stars and galaxies at their respective distances when a 'shift' can be seen.  Due to them flying away from us.

Which is not to say that it doesn't exist, and minor additional/counteracting red/blue-shifts are detected on certain stars, in a cycle, and indicative of a minor wobble in the star due to a sufficiently massive planet orbiting it, as well as differing degrees of shift at either side of a distant galaxy indicating the general direction and magnitude of spin of its main mass of stars, and the fuzziness of the signal showing the uniformity (or lack, thereof) of motion within that zone.

[Frelock]

You're correct Sean, in that the sun's main emission of light from blackbody radiation is green.  Combine Wien's displacement law with the surface temperature of the sun (you'll get around 501nm) and compare the result with the electromagnetic spectrum (500nm is in the green light range).  However, the main reason why we see the sun as a more yellowish color is because you've also got to take into account all the yellow, orange and red light its also producing.  There's more combined yellow, orange and red than there is green, so when you mix them all together, you'll get something yellow-like.  Gravity doesn't have much of an effect; you need a really sensitive instrument to detect it.

To answer your question from a while back, the difference between cosmic background radiation and distant galaxies is that cosmic background radiation is more or less stationary.  It existed everywhere at one point (shortly after the big bang, when the universe became transparent instead of opaque) so it can't be "moving" away from us.  Technically, we're seeing more of it, as more light reaches us and we see further away, but there's no relative motion of the stuff.  It's the background; the stuff on stage may be moving away, but the background stays the same (more or less).

[Sean Mirrsen]

To put a metaphorical spanner into relativistic works, how would you tell if background radiation was "background" radiation and not, say, reflected or emitted light flattened due to relative motion? If half the universe is moving away from us, there could be quite a lot of that.

Clarifying the explosion example from previously - I was explaining that "everything expanding from any given point" can be explained with a radial explosion. Some things receive less impulse and move slower, some receive more and move faster, and there are always some that have had the same impulse applied to them. Centered on one point, the explosion would therefore create an almost-uniform sphere of fragments. With little friction, the fragments would continue to move away, and would uniformly move away from each other. Particles with different initial impulses will move at different velocities, and particles with the same initial impulses will move away as the blast sphere expands. In any case, everything moves away from you, only in case of the Universe as we see it the particles are galaxies or galactic clusters. Fragments, in form of either energy or actual manifested protons/electrons/whatever, merged together due to gravity and kept growing in size until they became what they are now. Since each such cluster is supermassive, it accumulated particles from a large area, and its current velocity is an average of all those particles, making differences in velocity significant enough to be noticed.

(again, I'm forming this on-the-fly, with little forethought; I had no such explanation of galactic clusters' speed in mind when I made the example earlier; as this is just an extrapolation of the ambient energy theory, it requires no calculations to predict - may be inaccurate, but very useful for a writer or GM like myself ;))

[Flaede]

The way we worked out that the other galaxies are all moving away from us is because the light coming from them is red shifted. Amongst other things.

Wikipedia (as always) has moar.

I think that Flaede asked if there is any definite reason for favouring the "space expands, while locally gravity prevents it's expansion" over "space does not expand, but locally gravitation makes it shrink", which would, at least at a first glance, produce the same observational results. I.e. the expanding universe.

*glee*
yes. that was it. I'm glad someone could say that shorter and more concise than I could.

[Il Palazzo]

To put a metaphorical spanner into relativistic works, how would you tell if background radiation was "background" radiation and not, say, reflected or emitted light flattened due to relative motion? If half the universe is moving away from us, there could be quite a lot of that.

I believe that the key fact here is that the background radiation comes uniformly from every direction and is always of the same wavelenght. If you had light reflected of "something"(skipping over what it could be), then you'd have a broad spectrum of wavelenghts.
I myself find the idea of BR somewhat strange, after all, wouldn't it all just radiate away from the not-as-fast-as-light expanding parts of the universe? How come we can still detect it?

[dreiche2]

Hehe yeah BR seems funky, I never really thought / read about it.

I guess the question would be: Where should it radiate to? Basically, if you start in a situation where all of space is filled homogeneously with radiation; then at any given point, all light flow in all directions must be symmetrical. So in any given volume, the amount of light that leaves the volume is the same as that entering it. Ergo, the overall distribution must always stay homogeneous.

And this works as long as there are no 'sharp borders' of space as a whole, where light could 'leave' the universe, so either for an infinite space or a finite but looped space...