# Look out for that galaxy! *CRASH*



## J-Sun (May 31, 2012)

NASA'S Hubble Shows Milky Way is Destined for Head-on Collision with M31 (and maybe M33, too).

"I'm Robot 976QRZ3 with your morning traffic. A three-galaxy pileup was observed in the universe today. We suggest other galaxies with business in the area divert to..."


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## Vertigo (Jun 1, 2012)

Well it only confirms what we have long thought to be the case anyway.

So... fasten your seat belts, it may be a bumpy ride!


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## Venusian Broon (Jun 1, 2012)

Typical!

Always happens on a bank holiday weekend.


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## Metryq (Jun 2, 2012)

I guess someone forgot to press the clutch before redshifting. Galaxy collisions are very common.

Funny how that can happen when everything is supposed to be expanding away from everything else.


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## TheEndIsNigh (Jun 2, 2012)

... Although it'll all be over long before that.


I don't understand why this has hit the headlines recently. I thought this was very old news.




Vertigo said:


> Well it only confirms what we have long thought to be the case anyway.
> 
> So... fasten your seat belts, it may be a bumpy ride!


 




Metryq said:


> I guess someone forgot to press the clutch before redshifting. Galaxy collisions are very common.
> 
> Funny how that can happen when everything is supposed to be expanding away from everything else.


 
Something I've always puzzled about myself. Presumably this galaxy still has a red shift. That or someone has been telling porkies about everything in the universe moving away from us: red shift in every direction being the foundation of that particular argument.

Personally I'm an advocate of the 'multiple big bang' theory. If it can happen, why can't it happen again?


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## Venusian Broon (Jun 2, 2012)

TheEndIsNigh said:


> ... Although it'll all be over long before that.
> 
> Something I've always puzzled about myself. Presumably this galaxy still has a red shift. That or someone has been telling porkies about everything in the universe moving away from us: red shift in every direction being the foundation of that particular argument.


 
Galaxies have feelings too - they are attracted to each other! Hence despite the continual expansion of all space that drives everything apart some will indeed move and collide together because gravity compels them to. But most are sailing off away from us.

Oh and galaxies coming together have blue shift, not red



> Personally I'm an advocate of the 'multiple big bang' theory. If it can happen, why can't it happen again?


 
Well as long as I'm not around in the neighbourhood when it happens! 


I quite liked the 'Evolutionary Multiverse Model' where a new universe is created at some point inside a black hole with universal parameters slightly different - and random - from the parent universe (pure speculation of course, no idea how the author of this model was going to test it!) Hence over, loads of occurences and cycles, universes with the propensity to generate black holes would be most numerous. 

It's a bit of Russian doll existence for us, but some of the scenario's for the far future of the universe - heat death etc... are sooo depressing


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## thaddeus6th (Jun 2, 2012)

Metryq, that's a cunning point I'd never thought of before.

Hmmm. Quite glad the Venusian Broom was around to tidy up [puntastic!] that problem.


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## Venusian Broon (Jun 2, 2012)

thaddeus6th said:


> Metryq, that's a cunning point I'd never thought of before.
> 
> Hmmm. Quite glad the Venusian Broom was around to tidy up [puntastic!] that problem.


 
<_Gritted teeth mode on>_
Fight. The. Urge. To. Reply. With. A. Pun ...
<_/off>_

Anyway, I appear to be meandering,

Yours, 
Venusian Brook


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## thaddeus6th (Jun 2, 2012)

Cripes, sorry, I really did misread your name.


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## Vertigo (Jun 2, 2012)

TheEndIsNigh said:


> I don't understand why this has hit the headlines recently. I thought this was very old news.


 
Not quite. We have known for a long time that we _might_ collide with Andromeda but have not been able to make accurate enough measurements to know for sure. Let's face it if we have the measurements of the relative directions of motion of the two galaxies out by even the tiniest fraction of a degree then that will mount up to a very big difference over 4 billion years.

The point of the article is, I think, that they have now made more accurate measurements that confirm we will indeed collide.


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## Venusian Broon (Jun 2, 2012)

thaddeus6th said:


> Cripes, sorry, I really did misread your name.


 
No need to apologise, we shouldn't ponder morbidly about mispelling forum names.

Yours

Venusian Brood


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## Metryq (Jun 2, 2012)

Venusian Broon said:


> will indeed move and collide together because *gravity* compels them to.



That's an assumption that lead to Dark Matter—matter that is completely undetectable, except by its gravitational effect on galaxy structure. And then it doesn't create any lensing effects. (Can you say "ad hoc"? More like ad hoc ptui.)

I realize plasma cosmology is on very tenuous ground, also, but no worse than the theory that gravity drives the entire universe.

Do these Hubble results say whether or not the Magellanic Clouds will be involved? 'Cause I might want to move to my vacation house there until this collision thing is over with.


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## Venusian Broon (Jun 2, 2012)

Metryq said:


> That's an assumption that lead to Dark Matter—matter that is completely undetectable, except by its gravitational effect on galaxy structure. And then it doesn't create any lensing effects. (Can you say "ad hoc"? More like ad hoc ptui.)
> 
> I realize plasma cosmology is on very tenuous ground, also, but no worse than the theory that gravity drives the entire universe.
> 
> Do these Hubble results say whether or not the Magellanic Clouds will be involved? 'Cause I might want to move to my vacation house there until this collision thing is over with.


 
Not a great believer of Dark matter - currently I think it's a fudge to preserve Einstein's equations. Of course it may be true and there are vast numbers of exotic particles floating about around us not interacting very much, but my current belief would be that general relativity is wrong in some fundamental manner - (no idea what it is of course, so I'm not much help, but if I were to put a bet on it, I'd say it's something to do with black holes and singularities...)

However I'm reasonably confident that bodies with mass are attracted to each other in this universe one way or another; beliefs gained through personal experience and experimental data. And I don't need dark matter to predict that some galaxies being in close proximity to others will, if the conditions are right, move towards each other. 

Of course given current experimental data, gravity really doesn't have a say in this universe, given that it appears that the rate of expansion appears to be increasing. Which gives rise to my next bugbear, the great fudge of 'Dark Energy'. Again the assumption is that General relativity can't be wrong!


BTW, what's 'plasma cosmology'? Genuinely interested* Also what does "ad hoc ptui" mean. The Scottish state school education system did not touch upon the classical languages,at least when I was going through it 



* note: I'm not a complete believer of the current scientific orthodoxy, and in some cases reject it - so please don't think I'm deliberately 'toeing the party line' or deliberately opposing your remarks. I studied Physics to PhD level - although as you can probably see from my verbose, long and no doubt dull reply on the _Kepler_ thread, bog standard QM was my speciality.


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## Huttman (Jun 3, 2012)

TheEndIsNigh said:


> ... Although it'll all be over long before that.



Um...what will be over before the Milky Way and Andromeda collide?




TheEndIsNigh said:


> Personally I'm an advocate of the 'multiple big bang' theory. If it can happen, why can't it happen again?



I used to entertain that idea until recently I learned that everything is speeding up out there. Kind of intriguing, huh?


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## TheEndIsNigh (Jun 3, 2012)

Huttman said:


> Um...what will be over before the Milky Way and Andromeda collide?
> 
> I used to entertain that idea until recently I learned that everything is speeding up out there. Kind of intriguing, huh?


 
The End is Nigh. Galaxies colliding? Pah! In your dreams. The end will be a lot sooner than that!

Not sure why speeding up - by which I assume you mean, 'expanding quicker than it should', would affect your view. Multiple big bangs could happen both within and outside our current expansion. IE. there could be billions of expanding universes just over the horizon of our universe all having their 'pull' on our local expansion. 




Metryq said:


> That's an assumption that lead to Dark Matter—matter that is completely undetectable, except by its gravitational effect on galaxy structure. And then it doesn't create any lensing effects. (Can you say "ad hoc"? More like ad hoc ptui.)
> 
> I realize plasma cosmology is on very tenuous ground, also, but no worse than the theory that gravity drives the entire universe.
> 
> Do these Hubble results say whether or not the Magellanic Clouds will be involved? 'Cause I might want to move to my vacation house there until this collision thing is over with.


 
Regarding dark matter (and expanding universes for that matter) - I did have a thought recently along the following lines.

One of the odd qualities of light is that it is invisible. I did wonder what the total weight of all the photons that have ever existed, but have not yet interacted with something.

Moving away from our local expansion are thirteen billion years worth of photons, neutrinos, alpha, and beta particles - (short lived in air but, in the absolute vacuum of inter-expansion space?) and the like. In similar vein, at any one time inter-stellar/ inter galactic space would also have 13 billion years worth of these particles criss crossing the 'emptiness', at any one instant they would form a virtual sea of 'dark matter'.

So in my theory it comes down to :-

(for photon = read all the 'invisible' particles)

What is the weight of a photon?

How many photons are emitted from a source in any one nanosecond?

How many photons have existed since the universes began?

How many photons still exist? (99% as an estimate since collisions of photons with something else is so rare - just look at our sun's output)
What is the sum total of these particles?

How does that affect the calculations re dark matter/energy?


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## Venusian Broon (Jun 3, 2012)

TheEndIsNigh said:


> Moving away from our local expansion are thirteen billion years worth of photons, neutrinos, alpha, and beta particles - (short lived in air but, in the absolute vacuum of inter-expansion space?) and the like. In similar vein, at any one time inter-stellar/ inter galactic space would also have 13 billion years worth of these particles criss crossing the 'emptiness', at any one instant they would form a virtual sea of 'dark matter'.


 
My understanding of how we should interpret the current view of the universe is that there is absolutely nothing - not even empty space outside our expansion. (Correct me if I have misinterpreted what you have written, and I apologise in advance .) 

The big bang (if there was indeed one!) was not a giant explosion that took place in an infinite four dimensional spacetime. Spacetime itself was also 'unfurled' by the big bang.

The analogy I find most useful is that of a balloon. Take a balloon and paint spots on it - in this analogy the spots of paint represent the matter of the universe, and the rubber of the balloon skin is the dimensions of spacetime. As you blow up the balloon and it expands, the spots all get further away from each other. Matter and light are not allowed to leave the rubber of the balloon - there is no 'outside'. For the universe of course you have to add a third dimension, but the principle is the same. 

What this expansion is expanding into and has expanded from is a completely different matter - and a bit like the answer to the 1 divided by 0 - meaningless. In the sense that as it is outside our universe, how on earth can we experiment on it/look at it to discover what it's nature is. I'll leave it at 'formless potentiality' (FP) 

In some models, yes there are multiple big bangs - and I think the way to think about how they'd interact, using the balloon analogy, - is if two balloons are close to each other in this FP (although again it's a strange meta-distance we are talking about here, not a real physical distance) then they can influence each other by deforming each others skins as they expand next to each other, causing distortions etc... But you can't bridge between the two universes - they are seperate entities.





TheEndIsNigh said:


> So in my theory it comes down to :-
> 
> (for photon = read all the 'invisible' particles)
> 
> What is the weight of a photon?


 
Zero - photons are massless. But because they are energy and they are E-M fields they can impart momentum to particles. But that's not mass. 



TheEndIsNigh said:


> How does that affect the calculations re dark matter/energy?


 
As they have no mass and dark matter can not interact with Electromagnetic fields (otherwise we'd see it!) I'd guess that it doesn't.


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## Venusian Broon (Jun 3, 2012)

TheEndIsNigh said:


> Multiple big bangs could happen both within and outside our current expansion. IE. there could be billions of expanding universes just over the horizon of our universe all having their 'pull' on our local expansion.


 
Pondering about your ideas TEiN, there are theories of universes that do indeed behave a little like you describe there. 

Fred Hoyles Steady state theory* I think postulates a non-expanding infinite spacetime where mass is being continually created within it (I presume from 'little big bangs') and in this case you could theoretically look in on our local expansion...

..but, I believe these theories suffer in being even more incomplete than the Big Bang theory in trying to explain the data we have observed, i.e. are a bit 'handwavy' in trying to explain the observable universe. And as far as I'm aware has yet to predict anything that could be said to be solid evidence that this approach is right and the expanding universe is wrong.


* If there are any cosmologists out there with a much better understanding of the ins and outs that'd be really helpful!


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## Metryq (Jun 3, 2012)

Venusian Broon said:


> what does "ad hoc ptui" mean.



It's a bad pun. In comics one might see "sound effects" of a character clearing his throat and spitting written as "hoc-ptui!" (And of course, "ad hoc" is Latin "for this," meaning something done for a specific purpose, like an absurd patch whose only purpose is to save a flawed theory.)



> However I'm reasonably confident that bodies with mass are attracted to each other in this universe one way or another



Oh, no doubt about the attraction. I understand how the Big Bang model came about, but I also understand the many, many crippling holes in the theory. Yet many stubbornly resist _any_ attacks and defend Big Bang with the most absurd, Rube Goldbergish patches. Einsteinian Relativity is tightly bound up in Big Bang, so any attack on Big Bang is an attack on Einstein's sacred status.

When Kepler figured the orbits of the planets, he did not say what drove them. Similarly, Newton did not _explain_ gravity, he merely quantified it.

Somewhere along the line it was agreed that gravity drove the universe. And even absurd, _ad hoc_ creations like Dark Matter and Dark Energy, which allegedly make up 96% of the matter in the universe, have not led to a serious rethinking of Big Bang.



> BTW, what's 'plasma cosmology'? Genuinely interested*



As noted before, I'm not a professional scientist and hold no advanced degrees. But even the layman has a functioning baloney detector. Among the crazy stuff I've been reading:

THE BIG BANG NEVER HAPPENED by Eric J. Lerner—The Big Bang sounded fishy to me for a long time, and this was the first book I encountered that spelled out many of the problems. This was also my introduction to Hannes Alfvén and "plasma cosmology."

DARK MATTER, MISSING PLANETS AND NEW COMETS by Tom Van Flandern—This book is interesting for a variety of reasons. It details the various problems with Big Bang and some of the problems with Einsteinian Relativity. The author also describes the Meta Model, an alternative explanation for gravity based on LeSage's "corpuscular" gravity. Whether or not one agrees with the Meta Model, reading about it puts the Standard Model in perspective. Additional writings by Van Flandern can be found in PUSHING GRAVITY edited by Matthew R. Edwards and the MetaResearch Web site. (Full disclosure: I created a few animations for Van Flandern.)

SEEING RED: REDSHIFTS, COSMOLOGY AND ACADEMIC SCIENCE by Halton Arp—Arp's work is the single greatest blow to the Big Bang. Even more compelling is the response to his work: Arp was thoroughly ostracized. He was cut off from telescope and computer time and other resources, journals flatly rejected any papers, etc. Arp's work is not a mathematical model, it is actual observations showing a dynamic universe.

THE VIRTUE OF HERESY: CONFESSIONS OF A DISSIDENT ASTRONOMER by Hilton Ratcliffe—This book rounds up the books above (and others) and details the history of modern physics and cosmology.

And I'm currently reading THE ELECTRIC SKY by Donald E. Scott, and it's looking great so far.

I've read all the pop science stuff, too, like COSMOS by Carl Sagan, A BRIEF HISTORY OF TIME by Stephen Hawking and even THE FABRIC OF THE COSMOS by Brian Greene. That last book led me directly to NOT EVEN WRONG: THE FAILURE OF STRING THEORY AND THE SEARCH FOR UNITY IN PHYSICAL LAW by Peter Woit.

Physics Has Its Principles.


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## TheEndIsNigh (Jun 3, 2012)

Venusian Broon said:


> My understanding of how we should interpret the current view of the universe is that there is absolutely nothing - not even empty space outside our expansion. (Correct me if I have misinterpreted what you have written, and I apologise in advance .)
> 
> The big bang (if there was indeed one!) was not a giant explosion that took place in an infinite four dimensional spacetime. Spacetime itself was also 'unfurled' by the big bang.


 
Well... yes and no. There is at least 13 billion years of particles rushing out into that emptiness.

I would disagree with the photon being weightless. If it's a particle then its made of something. That something must have some mass, even if it's a billionth of the currently measurable units. Plus there's the old e=mc2 argument about the interchangeability of energy/mass thing.

However neutrinos are believed to have mass and there's a few of them  flirting about in the in-between-ness


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## Vertigo (Jun 3, 2012)

Huttman said:


> Um...what will be over before the Milky Way and Andromeda collide?


 
Well the sun will expand to a red giant in about 5 billion years and I think it's fair to say there will not be much life left on Earth a mere billion years before that...

Though of course we might have managed to expand to the stars by then, or more likely we will long since have vanished.

(Actually life on Earth is likely to become impossible in around 1 billion years)


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## Venusian Broon (Jun 3, 2012)

TheEndIsNigh said:


> Well... yes and no. There is at least 13 billion years of particles rushing out into that emptiness.


 
But not 'ahead' of our 'expansion' - they will be the edge of the expansion.

If you mean emptiness to mean our spacetime then I'd sort of agree with you (but it was never empty at any point). If you mean the Formless matter that our Spacetime is expanding into (and there are numerous theories), then I'd disagree with you. 



TheEndIsNigh said:


> I would disagree with the photon being weightless. If it's a particle then its made of something.That something must have some mass.


 
It's made of energy! EM flucuations. And no, just because it's a particle made of something, doesn't mean it has to have mass. Phonons in solids can exhibit particle characteristics, but are just vibrations in the crystal lattice



> even if it's a billionth of the currently measurable units.


 
Unfortunately, from a little digging around, the experimental limit on the mass of the photon appears to be 2.1x10-16 eV. For comparison the upper limit on the masses of the three neutrinos has been measured to be 0.28 eV. That's a 10^15 difference in magnitude. 

Of course this is just an experimental limit, I'd still bet it's zero! 



> Plus there's the old e=mc2 argument about the interchangeability of energy/mass thing.


 
E=mc^2 is a contraction of the more general complete relativistic expression of the energy of a particle:

E = (p^2 c^2 + m^2 c^4) ^1/2

Where p is the momentum. For a massive particle at rest p=0 and the equation reduces to E=mc^2. 

For a massless particle m = 0 the equation reduces to E=pc. Massless particles also can have energy!

Very high energy photons can generate electron/positron pairs. But you are bound by some very stringent conservation laws: Charge, Energy and Spin. Photons are Bosons with spin +/- 1 and no charge. Electrons are spin +/- 1/2 and charge -1. So to balance this process, you must generate a positron and an electron (no spontaneous generation of two electrons say). The goes for the other stable spin 1/2 particles, like protons. 

There is no such thing as conservation of mass in particle physics. Hence it's alright for a massless couple of photons to momentarily turn into two massive particles (and back again very quickly ) - it does not mean that these photons have mass.



> However neutrinos are believed to have mass and there's a few of them flirting about in the in-between-ness


 
Yes I agree. But even giving them the benefit of the doubt, their overall contribution to the mass of the universe is pretty negligle (for the shear numbers of them!)


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## Venusian Broon (Jun 3, 2012)

Cheers Metryq, 



> Among the crazy stuff I've been reading:


 
I will give them a look out and a perusal if I can find them. 



Metryq said:


> Einsteinian Relativity is tightly bound up in Big Bang, so any attack on Big Bang is an attack on Einstein's sacred status.


 
To be fair to Relativity it doesn't require Big Bang theory. And conversely Big Bang theory doesn't require Relativity. If Big Bang was ruled out as never happening tomorrow, it doesn't impact the validity or not of Relativity. 

The way I'd put it is, that the form and philosophy of General Relativity is an examination of the nature of our large scale view of the universe. 

The big bang theory is an examination of the set of assumptions or boundary conditions that perhaps explain the past development of the universe. Hence it uses a _specific_ solution of General Relativity (as the consensus is it's the most valid description of the large scale universe - of course if you disagree you don't need to use it!), as well as results from particle physics and QM. 



> And even absurd, _ad hoc_ creations like Dark Matter and Dark Energy, which allegedly make up 96% of the matter in the universe, have not led to a serious rethinking of Big Bang.


 
I agree that they are serious fudges, but personally I think they point to problems with Relativity rather than Big Bang. 

Oh and if we're listing fudges, let's make it a triumvirate and include Inflation. I think that's the weakest point in the Big Bang theory by far - it's practically a cheat


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## Metryq (Jun 3, 2012)

Mmmm, fudge!

Thanks, Venusian Broon. Ever taken the Theological Engineering Exam?


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## Venusian Broon (Jun 3, 2012)

Metryq said:


> Thanks, Venusian Broon. Ever taken the Theological Engineering Exam?


 


I fell a bit sorry for Cornelia stuck in the alligator. 

Anyway we appear to be way off the topic regarding the collision of galaxies, so in the event that a collision was going to be imminent I think it would be important to know how to hunt elephants


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## Metryq (Jun 3, 2012)

The slowly rising pitch (Doppler effect) of the approaching galaxy is still well below human hearing, however the elephants, giraffes (and cetaceans) already knew the collision was coming.


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## Huttman (Jun 4, 2012)

Venusian Broon said:


> The big bang theory is an examination of the set of assumptions or boundary conditions that perhaps explain the past development of the universe.



It is also an astute, keen and witty television sitcom


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## Venusian Broon (Jun 4, 2012)

Huttman said:


> It is also an astute, keen and witty television sitcom


 
Although I know of some circles where comments like that are more contentious than the actual validity of the real phyiscal theory 

For the record, I do like the show quite a lot!


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## Metryq (Jun 4, 2012)

Venusian Broon said:


> Although I know of some circles where comments like that are more contentious than the actual validity of the real phyiscal theory



Indeed, the elephant in the room. (Corollaries to Sturgeon's Law)


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## RJM Corbet (Jun 7, 2012)

TheEndIsNigh said:


> So in my theory it comes down to :-
> 
> (for photon = read all the 'invisible' particles)
> 
> ...



No, I think photons are massless.

They are emitted as quanta when an electron drops from one energy level to the one below, at least some of them are? As pure energy, they behave both as particles and as waves.

1 quantum per 'transaction'.

Dark matter is what's holding the universe together.
Dark energy is what's pushing it apart.
Because something needs to account for the discrepancy between the gravity and the 'perceivable' mass of the universe.

I personally like the 'multiverse' idea, where only gravity operates through all the universes, and we just get a bit of it.

Call it dark energy, call it God, doesn't matter the name.

I think of it as a chessboard, the pieces are restricted to move upon the flat plane of the board (but in four dimensions) while the forces that really direct the (nevertheless infinite) movement of the pieces, operate from a higher dimension that surrounds and contains and permeates the dimension where the game appears to be happening, but are not themselves contained by or restricted to that dimension, having lots of other concerns as well, beyond the game of chess.

EDIT: Vertigo: one of the worlds in my story is one where the insect life have survived the 'red giant' phase, and have, in the millions of years since then, evolved into an intelligent, spacefaring (at below light speed) civilization, on a freezing world beneath a dying star ...


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## Gordian Knot (Jun 22, 2012)

As for the ol' everything is moving away from everything else. Well. Yes. And no.

Yes everything in the Universe is expanding outward at ever faster rates.

BUT

"Local" galactic objects are being attracted towards each other. That is why the Milky Way and Andromeda galaxies will meet up a few years down the road.

Indeed everything in what is called our Local Group, which is a verrrrry big neighborhood, is being pulled towards something appropriately called The Great Attractor. The GA is 250 million light years from us!


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## THX-1138 (Jun 25, 2012)

Venusian Broon said:


> Not a great believer of Dark matter - currently I think it's a fudge to preserve Einstein's equations. Of course it may be true and there are vast numbers of exotic particles floating about around us not interacting very much, but my current belief would be that general relativity is wrong in some fundamental manner - (no idea what it is of course, so I'm not much help, but if I were to put a bet on it, I'd say it's something to do with black holes and singularities...)


You mean like this?
http://en.wikipedia.org/wiki/Modified_Newtonian_Dynamics


Venusian Broon said:


> Fred Hoyles Steady state theory* I think postulates a non-expanding infinite spacetime where mass is being continually created within it (I presume from 'little big bangs') and in this case you could theoretically look in on our local expansion...


There was a recent book about that.
http://www.amazon.com/dp/145162445X/?tag=brite-21
Somehow mass can come from empty space apparently. Or this author thinks so.


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## Shane Enochs (Jun 25, 2012)

Just throwing this out there, but since the size of our galaxy is gigantic, isn't it possible that the galaxies have already collided, or something else has already happened considering we're looking a hundred thousand years into the past when we look at the other edge of our galaxy?


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## THX-1138 (Jun 25, 2012)

Actually we can't look at the other edge of our galaxy. There's to much dust.

Do you mean andromeda and the milky way have already collided? No, that's impossible. Two other galaxies have collided to form the milky way? I suspect that's possible, but I don't know.


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## RJM Corbet (Jun 25, 2012)

EDIT: I was going to say something, but put my mouth into gear before my brain was in action ... again


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## Vertigo (Jun 25, 2012)

You can never look back that far in time within our own galaxy, it's just too small. It's around 100 thousand light years in diameter. So if we could see the light from the far side of our galaxy we'd still only be 'looking back' around 100,000 years. Whereas the 'collision' isn't due for around 4 billion years.


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## Mirannan (Jan 23, 2013)

Photons have no rest mass but have mass equivalent to their energy divided by c^2. Photon energy is dependent on frequency, so gamma-ray photons are heavier.

Mathematically: Tau factor at c is ∞. If rest mass is zero then m = 0 x ∞ which is undefined or indeterminate.

Roughly speaking!


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