Relativity Question

[CraigS]

Ok all you relativists out thar .. he's a conundrum question I've been trying to wrap my mind around for a while … this has to do with cosmological event/particle horizons ...

Say there are two exo-galaxies out there, galaxy X and galaxy Y, where X is nearer to us than Y. Now with cosmic acceleration, there will be some last photon from either galaxy after which we will see nothing. Now, at the time X sends out its last photon, there will also be a Y photon passing by X. They both travel at the same speed, and thus they both reach us at the same time (Y will be more redshifted than X). We will see both galaxies blink out together, even though Y is further away (and is presumably younger than X).

So if we think of the entire universe consisting of galaxies of different ages, then this would mean that at one instant we will see our entire observable universe …. and in the next instant … all of it blinks out ??

There is some flaw here, but where is it … ??...

Answerers welcome.

Cheers

[SkyViking]

But there won't be a 'last photon' will there?
The cosmological redshift will merely shift and dim the light until the point where we can no longer detect any signal from them, it will just get lost in the CMB eventually. And that will all happen for galaxy Y first.

[Archy]

I can understand a redshifted spectrum: how can the "redshift" of a single proton be measured:help:

[renormalised]

Photon....not proton. Very easily, with a photomultiplier tube and in exactly the same way as you measure a redshifted spectrum. You look at (or determine via theory) what the original wavelength/frequency of the photon was when it left the source and compare that with what you measured at the photomultiplier.

[CraigS]

Thanks Rolf.

For this hypothetical example, I'm trying to ascertain whether or not there is a theoretical limit, so I've kind of assumed the CMB is out of the scope. I think this just makes it a bit less complicated .. (?)

So is what you say then, not just a practical detection issue ?
Ie: build a more powerful detector commensurate with the increase in redshifted wavelength/decrease in power ?

What I'm trying to ascertain is will the accelerated (metric) expansion of space mean that there will be an instant when both photons are simply not able to reach us - ie: we are causally disconnected ?

Cheers

[michaellxv]

IFF your original statement is true that would imply we can currently see the entire universe.

A question to help my thinking.
Galaxy X and Y are currently receding from each other at a rate R. Photons can travel between X and Y and they can see each other.
The rate R is increasing and at time T reaches C. At time T a photon can not complete the trip between X and Y. Assuming there were a continuous stream of photons along the path what happens to these photons at time T? Are they all trapped at their point in space at time T? Does this also imply that every point in space along the path is expanding at a rate of C? Does this mean that your original statement is true and all galaxies blink out when all of space is expanding at a rate of C?

Having typed this out it still doesn't sound right but i'll leave it anyway. I think it would contradict all of Hubble's observations.

[SkyViking]

On a second thought, I think that strictly speaking yes there is a 'last photon', but by the time galaxy X emits the last photon that will ever reach us, galaxy Y has already passed beyond the event horizon. So there won't be a Y photon passing by X at the time.

[sjastro]

If galaxy X is at the horizon, galaxy Y is already beyond that horizon and hence photons from Y are unobservable as the recession velocity of Y is greater than C.

Despite the fact that galaxy X is accelerating faster than galaxy Y because X is younger than Y, the Hubble "constant" increases with decreasing cosmological time. Since galaxy Y is older than galaxy X, the Hubble "constant" is larger at the time when say galaxy Y is formed. The recession velocity for galaxy Y will always be greater than that of galaxy X.

While this might seem counter intuitive as X is accelerating at a faster rate than Y, it's very easy to explain mathematically.

Since the Universe is expanding metrically, the scale of the Universe increases with time.
Suppose R(t) is the scale of the Universe at some time t, then dR/dt is the rate of change of the scale R(t). dR/dt is the acceleration of the Universe.
Hubble's "constant" H is simply (dR/dt)/R(t).

Since galaxy Y is formed before galaxy X, the scale R(t) is less than at the time of the formation of galaxy X. Since you are dividing by a smaller number, the Hubble "constant" is greater at the time of formation of galaxy Y despite dR/dt being greater at the time of formation of galaxy X.

Hence the Hubble "constant" and therefore the recession velocity of galaxy Y will always be greater than galaxy X.

Regards

Steven

[CraigS]

Thanks Steven (and all - much appreciated);

I suspected the answer was in the formal definition of the acceleration/Hubble "Constant".

However, I'm still a bit perplexed because that photon that was emitted by Y, and was adjacent to galaxy X just before X made it to lightspeed, should still arrive at Earth at the same instant as X's last photon (??)

We loose sight of both at the same instant (??) Even though we'd lost sight of Y before X ?? :screwy:

(Sorry if I'm being slow on the uptake here .. there is more than one frame of reference involved in this ..)

Cheers

[Robh]

Hi Craig,

I'm not sure but I suspect that the answer lies in time dilation due to the differences in relative velocity resulting from the accelerated expansion of space. This time dilation can be less for particles arriving from Y to X but much much greater for particles arriving here from X and more from Y.

The images of the galaxies don't actually disappear but are frozen in time as they pass the cosmic event horizon. Any further information (e.g. photons from Y) after it passes the event horizon no longer reaches us.

This is similar to the event horizon of a black hole where the image of an ingoing object is seemingly frozen at the event horizon to a distant observer.

The effect is relative to the different reference frames from which the photons are being observed.

Regards, Rob

[CraigS]

G'Day Rob;
Long time .. no hear .. good to see you back in these parts ! :hi:

I was having recall about our previous discussions about the similarity of this and BH Event Horizons. I think I recall leaving that discussion with the QM/String Theory view that 'frozen' images break into ever increasing smaller components (vibrating strings) covering the entire EH. At the moment though, I'm trying to get the Relativity perspective embedded in my brain. The relativists seem to always refer to the 'blinking out' phenomenon and I think this is derived from the formal definitions posted by Steven. (I'll have to have more of a think about the ramifications of these).

There's another issue also .. raised by Rolf … the redshift one. In theory, redshift would cause the wavelength to become just about infinite wouldn't it ?

What happens to the energy of the photon if/where this happens ?
:shrug:
Cheers

[Robh]

Craig,

The light is not just red-shifted in the visible spectrum. The more distant object will be progressively more red-shifted, which makes it harder to detect in the visible spectrum, then harder to detect in the infrared, microwave and radio spectrums etc. The photons are moving progressively along the spectrum as the object is further away.

That is, the light (photons) do not blink out at the same time for galaxy X as the further galaxy Y. It is a gradual process.

Rob

[CraigS]

In an accelerating universe, there must come a point where the photons can never feasibly make it to Earth, because they are beyond our Cosmo EH. This would be independent of our inability to detect infinitely big redshifts though .. I suppose the question would be … which comes first: the 'blink out', or; the disappearance due to diminished light.

And, if we could build a radio detector big enough, perhaps we could still go on 'seeing' the ever increasingly redshifted photons from Y. If we could tap into the energy of our newly expanded universe, we might have enough energy/power to pump into the detector, too.

(I'm talkin' the extreme limits here, also .. so its another one of 'those' hypotheticals … but the theory must tell us something about the limits and which phenomenon happens first ??)

Cheers
PS: I still can't see why X's and Y's co-incident photons wouldn't arrive simultaneously and then, spectacularly, blink out together .. :shrug: I tend to agree that the process you mention would be a gradual one and intuitively, I agree with you .. what I'm trying to do is to understand why the logic in my original post is in error … (I'm sure it is .. 'intuitively'.)

[sjastro]

This is a consequence from the Robertson-Walker metric (http://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2% 80%93Robertson%E2%80%93Walker_metri c). The event horizon incidentally for a BH is based on a gravitational redshift mechanism, not a cosmological redshift or time dilation mechanism.



Cosmologists prefer to define the frequency of light rather than it's wavelength for a very good reason. Frequency has the units of reciprocal time. Cosmological redshift is a result of time dilation as derived from the R-W metric, rather than the wavelength stretching. The stretching of the wavelength implies loss of energy which leads to the tired light hypothesis.



Nothing at all happens. The tired light hypothesis is elegantly refuted by our friend Ned Wright.
http://www.astro.ucla.edu/~wright/tiredlit.htm

Regards

Steven

[CraigS]

Ok Steven;

So, I'm on track with this now .. no problems ..

So, I guess, as Rob mentions, the Y photons experience more time dilation when compared with the X photons .. I would expect that this would impact their relative arrival times, perhaps to the extent of Y's photons not arriving at all (unlike as I originally hypothesised ?). If so, then that problem's solved.

The next issue is if nothing at all happens to the photon's energy (ie: it remains constant), then does this also imply that the energy density of the expanding obs. universe has dropped, due to the expansion of our hubble sphere, which has happened as photon Y makes its way (alongside photon X), to our scopes ?

Cheers
PS: Ned says .. 'yes' .. as per observations ! (I just read Ned ..).

[CraigS]

So, photons "blink out", and also diminish from our abilities to detect 'em because of extreme redshifts, eh ?

So, which happens first .. and;
Does this phenomenon define the difference between a merely expanding universe .. and an acceleratingly expanding one ?

Cheers

[Robh]

Thanks Steven, that makes sense.

Regards, Rob

[sjastro]

I wouldn't want to disagree with Ned.:sadeyes:
Imagine if he appeared in Thunderblogs.:eyepop:

[CraigS]

Ok .. done some reading .. from Wiki it defines the Particle Horizon: (http://en.wikipedia.org/wiki/Particle_horizon#Particle_horizon)

and then .. it makes the distinction ...


They give two equations for the particle horizon and then the cosmic event horizon.
If you add the particle horizon and cosmological horizon equations together, that should equal where the boundary is at any one time, right ?
Ie:
particle horizon + cosmological horizon = 'the boundary'.

Cheers
PS: Err .. the boundary being the difference between what we can see and what we can't see yet .. but will in the future ..

[renormalised]

That would be like the devil turning up in St Peter's wanting an audience with the Pope!!!!:P:eyepop::D

[sjastro]

Photons "blink out" because they no longer reach the observer. Due to time dilation they no longer have the time reach us.

In an accelerating Universe, objects that are now at or near the horizon will eventually disappear.
In a merely expanding or inertial expanding Universe there is a gradual slowdown (but still infinite) expansion. The opposite can occur. Objects that are just beyond the event horizon may become visible later on.

Regards

Steven

[CraigS]

Ok .. just drumming it into my brain:

There's light emitting things (galaxies, quasars, S/Ns, etc) that:

i) we can presently see;
ii) we can't presently see, but we will be able to see in the future (and we'll see them in their infancy);
iii) we can't presently see .. and never will see (causally disconnected).

However, for type (ii) above, it is conceivable that the light we eventually receive from these things will be redshifted to the point of being physically undetectable anyway, so we are causally disconnected from it anyway.

We should improve our technologies for detecting sub-mircrowave, otherwise we'll miss all the action !

Who is to say that we're not already missing stuff which happened > 13.7 billion years ago, just because we haven't built a detector which can receive it ?

Cheers

[renormalised]

You mean further than 47.5Gly comoving distance. Anything older in 13.7Ga light travel time and we'd be seeing.............................

If they're over the event horizon now, we will never see them because they will always be traveling faster than c. The curvature of spacetime for these objects will always be too great for the light to traverse to us. Especially since the Universe appears to be accelerating in its expansion.

[Robh]

Craig,

I often forget about the scenario of your point (ii).
One of the purposes of the James Webb Space Telescope was to partially bridge this gap i.e. pick up the infra-red spectrum. The Hubble has had great success in the visible spectrum.

A pity that the James Webb is in danger of being canned because of lack of funding (today's news).

Regards, Rob

[renormalised]

The US is going backwards...all because of the idiots running the place. Don't be a bit surprised if NASA becomes in danger of folding completely if they keep going along their present course.

It would be a great shame if they can the JWST. And a huge waste of money.

[Robh]

A bit off the track but interesting blog on the JWST, funding and purpose.
Love the enthusiasm displayed in the video.
http://blogs.discovermagazine.com/cosmicvariance/2011/07/07/why-we-need-the-james-webb-space-telescope/

Rob

[CraigS]

Err … yep.

The limits of the equations in the Wiki article I mention in my previous post are interesting when viewed from accelerating and non-accelerating universe perspectives … might do some more thinking about these ..
.. Interesting ..

Cheers

[CraigS]

They (the US House of Representatives Appropriations Subcommittee on Commerce, Justice, and Science), voted against further funding in the next year, eh ?
NASA's backed off and said it'll try and launch it in the next decade (2018 at the earliest ?)

Not good.

Cheers

[CraigS]

Thanks for the help … everybody.

Everytime I revisit this topic, I come away with a different perspective on it all.
(Will that ever change ?)
:)
Cheers

[CraigS]

Just for a laugh ..

I should say I neglected to mention that photon Y was originally emitted by an AGN containing a quasar ... and therefore was 'immune' from the effects of time dilation.
:)
Cheers

[Archy]

Sorry, I meant photon
Yes, you can measure the wavelength/frequency of the photon when it arrives, but how do you determine what the original wavelength/frequency of the photon was when it left the source?

[Archy]

If relativity applies, how does a photon become immune

[sjastro]

Relativity also "applies" to non expanding cosmological models where time dilation doesn't exist.
Metric expansion (cosmological redshift) is a property of the cosmological model not GR.

The only form of redshift which is derived by GR/SR is gravitational redshift.

[Archy]

Don't beat around the bush: how does a photon become immune

[renormalised]

He's not, he's trying to answer your question directly.

How does a photon become immune....no one really knows. But if you look at the timing of light pulses in the variability of the quasar's central regions, you find that no matter how far away or close the quasars are, the variability occurs at roughly the same time intervals. Meaning that the light coming from these objects is not subject to time dilation due to cosmological expansion. There could be several explanations for this, the first being there is a population of very massive objects scattered randomly across the universe between us and the quasars...namely small black holes. But observations so far discount this possibility. Another is that the quasars are not at the distances their redshifts say they are, which means the BBT is wrong and we need to figure out why (look at Steven's answer). Or, there is something wrong with SR/GR w.r.t. quasars and we need to find out why, also. There maybe other reasons, but it's late and I'm off to zzzzland:)

That's the long and short of it.

[sjastro]

Evidently my response went over your head, so let me try to make as simple as possible for you.

The mathematical equations behind GR cannot be solved directly. Solutions have been provided by a process similar to reverse engineering, a solution is constructed based on certain physical assumptions. The solution is then plugged into the field equations. If they satisfy the field equations you have a model you can build on.
Cosmological models are built on this foundation. The important point is that GR provides the gravitational theory for these models and that the physical assumptions of the model do not violate the field equations.

A typical physical assumption for a cosmological model is whether the Universe expands, contracts, oscillates, rotates or remains static.
There are various cosmological models reflecting these scenarios all of which conform to the field equations. GR doesn't determine these assumptions.

As Carl has pointed out time dilation is a property of an expanding Universe cosmology, not a relativity issue.

[CraigS]

I like beating around the bush … why don't you ?

[avandonk]

Actually Craig the two photons are everywhere and everywhen in all the Universes. They have followed all possible paths before they set off. You have no way of proving any alternative until you measure them. Then you are stuck with a result you cannot understand.

It is far more satisfying to beat around the bush! Completely pointless but satisfying.

Bert

[CraigS]

Bert;
Are you tellin' me that we can't gain any understandable knowledge of the physical world from the Science of Astronomy ? :sadeyes:

Bear Grylls beats around bushes … and he's a living legend !

Cheers

[renormalised]

And he uses a large stick:D:P

[avandonk]

The bush I like to beat about is totally obvious!
Bert

[CraigS]

:lol:

[renormalised]

George "Dubya"???:):P

With a baseball bat??:):P

It's all "relative" anyway:):P

[avandonk]

I have enjoyed my whole life by facing the bush face or head on. It cannot be ignored. It needs nurturing as we come from the bush. It is not for nothing all Aussies head for the bush on long weekends.


Bert

[Archy]

What an arrogant reply!

You say:
"time dilation is a property of an expanding Universe cosmology, not a relativity issue."

Yet Wikipedia says:
"Gravitational time dilation is the effect of time passing at different rates in regions of different gravitational potential (http://en.wikipedia.org/wiki/Gravitational_potential); the lower the gravitational potential, the more slowly time passes. Albert Einstein (http://en.wikipedia.org/wiki/Albert_Einstein) originally predicted this effect in his theory of relativity (http://en.wikipedia.org/wiki/Theory_of_relativity) and it has since been confirmed by tests of general relativity (http://en.wikipedia.org/wiki/Tests_of_general_relativity)."

[CraigS]

Accusing others of 'beating around the bush' is guaranteed to solicit a response in kind.
This wording implies that you know the intentions of the respondent before he has stated them.

How do you know this ?

I for one, understood Steven's considered response and I thank him for it.

Cheers

[renormalised]

Excuse me, but you need to reread and understand in what context you're trying to place time dilation. What you have contextualised in time dilation is in response to the expansion of spacetime. In which case, there is no issues regarding relativity, only as a property of expanding spacetime cosmology. So, it is you that has misunderstood your own question.

This is precisely why most people get their knickers in a twist over science when they ask questions and expect certain answers. You don't understand the science in the first place and you only paraphrase what you've read. Quoting websites isn't going to give you the answers to your questions, nor is it going to contradict the answers of others unless those others have got the answers wrong themselves. Steven knows exactly where he is coming from...his degrees are in applied maths and physics.

If you want to know about science, fine, read up about it. But if you want to understand it, learn off someone who already knows about it as well. Understanding comes through asking questions about those subjects you read. You won't get that through rote learning.

[sjastro]

You obviously have a problem with basic comprehension skills.

Here is my original quote.



The discussion centres around time dilation effects due to cosmological redshift not gravitational redshift.

[Archy]

You skirt around my original question and you answer with insults: is this the best you can do?

I repeat:

I can understand a redshifted spectrum: how can the "redshift" of a single photon be measured:

[Archy]

You skirt around my original question and you answer with insults: is this the best you can do?

I repeat:

I can understand a redshifted spectrum: how can the "redshift" of a single photon be measured:

[Archy]

Still beating around the bush
You skirt around my original question: is this the best you can do?

I repeat:

I can understand a redshifted spectrum: how can the "redshift" of a single photon be measured:

[CraigS]

I like to skirt around questions .. don't you ?

[Archy]

This is the best you can do!

[CraigS]

Is that the best you can come up with ?

[renormalised]

Just what is exactly your game here???. Are you just going to keep repeating yourself and throwing our answers back in our faces??

Or, are you just trying to be funny or think yourself smart by being facetious.

If you can't understand what I (or the others) wrote then you really need to back away from this subject because all you'll do is just make things harder on yourself.

Put it this way, if you can understand a redshifted spectrum, then you should understand how a redshifted singular photon is measured. If you can't, then why should I (or anyone else) even bother trying to explain it to you. It would be a waste of time. However, for the record, you also wanted to know about the immunity of a photon from time dilation. You were told why yet it's very apparent you either didn't believe the explanation and/or didn't understand it. Most likely both. That's your prerogative, but don't come out and arrogantly accuse anyone here of "beating around the bush" when it's supremely evident from your puerile responses that you're all too eminently good at it yourself.

[sjastro]

Archy,

Is it really worth being argumentative at the risk making yourself look more and more foolish in the process?

This thread like your posting history in the Science forum in general, clearly indicates a willingness to pick fights with individuals instead of making a positive contribution.

I am not going to waste my time in engaging in fights.

[Archy]

A long reply, but no answer to the question

[renormalised]

It wasn't an answer....that, I and others gave to you beforehand. If you don't want to listen, fine. Find your answers elsewhere.

[bojan]

I think that the question above deserves a more precise technical answer (because it is a precise technical question... and myself being an engineer, I am reducing theoretical problems to "how to do something", and not "why something happens").

When we measure the spectrum redshift, what is really measured are the wavelengths of the absorption or emission lines of atoms or ions of specific elements, identified as such - so we know the difference between the original wavelengths (or, we are assuming we know) and the received ones.

If I received one single photon with my test equipment, I must admit I wouldn't know what to do with it - apart from recording it's energy (which then directly translates into wavelength of course... and photomultiplier tube will not do this job, BTW). And that's about it. I wouldn't have a clue about process that generated that particular photon, so I can't possibly determine it's redshift.

I believe THIS was the core of the question in question.

[renormalised]

That's what he was told before, except that the photon can have its redshift measured. Remember, he's wanting to know the answer for a photon coming from a source that is itself being redshift by cosmological expansion. It's a simple exercise in working backwards to find the wavelength of the photon at its point of origin.

[CraigS]

… And I was content with the answers everyone gave me, to my original question.

I don't think anyone providing helpful answers, interpreted the basis of my original question to be in any way dependent upon a single measurement of a single photon. There is clearly a time element basis to the question. How could the last photon be interpreted as the last photon, unless there was a context (meaning a history of measuring a photon stream or spectrum, which ends up actually defining the last photon ??)

I think both questions about time dilation and redshift being interpreted on the literal basis of a single photon, were way out of context and yet, the question clearly was all about the context.

Whilst any questions in threads are usually welcomed here, standover demands for answers for out of context questions get what they deserve. Unless I'm mistaken, I don't believe anyone here is under an obligation to answer anyone's questions either. They do so out of generosity and a commitment of contributing value to the site.

Recently, I have noticed that this message seems to have been sadly forgotten (across multiple threads).

Thank you to all answerers who actually contributed to the value parts of this thread. They are much appreciated.

Cheers

[sjastro]

The fact that I have been similarly accused of not answering this question is quite interesting given that I have not been involved in this specific part of the thread.

My involvement in this thread was to point out to the "gentleman" concerned the issues of equating relativity with cosmological redshift, to which I got the "question" in response.

Now this this question has absolutely no relevance in this context. In fact it is just a blatant diversionary tactic.

So I wouldn't place any credibility on the question in the first place.
The question is loaded because irrespective of how one answers it, one will always be wrong.

The best thing is to ignore the question.

Steven

[xelasnave]

I had a look around Steven and there are many sites dealing with that question and I see your point:thumbsup:.

alex:):):)

[bojan]

You are right in terms of intentions of the author of the question.

However, I still think the ONLY way to debunk those diversions is to answer the questions accurately, with all necessary argumentation as to why it is not relevant - without rising voice.

Ignore the intentions, not the question.

This is not for the sake of this particular author, but because of other spectators who may not know what is going on, but who will take sides, and it will be very likely the wrong one (David vs Goliath and so on...).

We may not be "official teachers" here (as Craig mentioned earlier) but this fact still does not absolve us from responsibility of allowing the in-accurate and plainly wrong ideas to spread. And, other spectators (who do not necessarily take part in discussion) will learn more from full answers (including myself).

My 2 cents...

[CraigS]

Well, just recapping, a polite answer was provided ... way back in post #4. (http://www.iceinspace.com.au/forum/showpost.php?p=741122&postcount=4) If the answer wasn't sufficient, it doesn't take a lot of effort to politely request more info. A completely different question was posed is in post #34 (http://www.iceinspace.com.au/forum/showpost.php?p=742325&postcount=34) and I don't consider this to be a polite request ! And then, somehow the original question was once again posed, impolitely, to the wrong person in post #49. (http://www.iceinspace.com.au/forum/showpost.php?p=743498&postcount=49)

Seems to me the more important question here should be posed to the questioner as to why he's so impolite (??) !

Cheers

[sjastro]

I largely agree with you but if the author's motives are based on a personal agenda then the Science becomes irrelevant. It doesn't matter how well you the explain the problem, if the author's objective is to discredit you rather than the Science, then there is no point in engaging in any form of discussion.

In this case all the author has to do is to regurgitate the same argument or introduce a totally irrelevant response.

Regards

Steven

[xelasnave]

this may be of interest

http://www.sciencedaily.com/releases/2011/06/110630161834.htm

alex

[Archy]

I asked how can the "redshift" of a single photon be measured

Renormalised replied "...Very easily, with a photomultiplier tube and in exactly the same way as you measure a redshifted spectrum. You look at (or determine via theory) what the original wavelength/frequency of the photon was when it left the source and compare that with what you measured at the photomultiplier."

Bojan replied inter alia


Bojan's reply that the redshift cannot be measured contradicts Renormalised. I agree with Bojan the redshift of a single photon can't be determined. Others in the thread were unwilling or unable to answer the question. When I pressed for an answer gave wrong, irrelevant or evasive replies and cast aspersions on my motives. Gentlemen, whether you answer questions or not is your prerogative: but what you have indulged in just wastes space.

[renormalised]

No, you chose one reply which was not based on anything to do with your initial and subsequent inquiries. Bojan stated that because he had no clue as to what the source of the original photon was, he couldn't measure anything other than its energy as registered on his equipment.

So, all you are trying to do here is pit one person's answer against another and try to make something of it.

My initial reply to your question was correct and is as correct as Bojan's. If you know the source of your photon, it's a simple matter of working backwards with the observation and using the appropriate redshift equations to give a redshift for that photon. And all you need is the photomulitplier tube (which will do the job, if you know how to convert the measured intensity to wavelength) to find the wavelength of the photon at detection.

Exactly the same way they read a redshifted spectrum.

If you can't understand that, then you shouldn't have asked the question in the first place.

Or, are you just out to cause arguments.

[sjastro]

What was the relevance of your question regarding cosmological redshift and relativity?

[CraigS]

I learned much from the discussion .. with my being such a valuable person, I'm going to authorise this usage of the space.
:lol: :)
Cheers

[renormalised]

Where's your stamp of authorisation:):P

(and it's got to make a big "kerchunk" noise when you stamp it down on the page):):P

[Archy]

My you are all riled up. The original question started and ended thus


Perhaps you are riled because the flaw in your postulate is that although you can measure the wavelength/frequency of the photon when it arrives, it is impossible to determine what the original wavelength/frequency of the photon was when it left the source, though you may speculate what it was.

Therefore you cannot determine the relative ages of photons X and Y

Giving facile or abusive responses tends to cloud the issue.

Gentlemen, Goodnight

[sjastro]

I'm still waiting on your answer.

[renormalised]

Being "smart" about it will not make your reply any less puerile.



Let's make it clear right from the start....the relative ages of any photon have nothing to do with the question that you specifically asked. Your question has nothing to do with the original question of Craig's.

Your responses show a clear lack of understanding either our answers or any of the physics involved. I doubt very much if you'd understand the original question that was posed.



Don't try and sound all reasonable. It doesn't work. Yours is a case of the pot calling the kettle black.

[CraigS]

Well, ok .. so that doesn't really provide me with any insights into explaining anything I observe …

So I'm now in alignment with Steven's question … how is this relevant in my quest to explain what I might see ?

Cheers

[avandonk]

I should have answered more informatively.

A very smart lecturer taught me years ago

One observation was just a point.
Two observations only imply a trend.
Three may give you a straight line trend.

It is only through many observations with all available means can we work out how things tick. These observations should fit any theory and be self consistent across all scientific fields. Like QM and gravity!

Astronomy is not an isolated science. Of course this is stating the bleeding obvious but it needs to be said.

A gedunken experiment based on two photons with the dubious honour of being the last from their respective sources will never give any insight no matter how carefully 'measured'.

Our reality is the constant interaction of uncountable energy interactions that all affect each other and further interactions ad infinitum. When the interactions stop reality stops. All of us come from the dust and gases from many stars and supernovae. The coldest places in our galaxy are even now accreting dust and gas for new stars and planets. Gravity can only collect this nebulous material when it slows to a crawl.

I wish I could explain my ideas better but like most humans I am limited by my own ignorance and time and space on this forum. My interpretation of the Universe changes as I get older and all are 'correct' as they are all equally wrong!

Bert

[CraigS]

I'm beginning to see that in order for it to do so, there needs to be a commonality of background understanding. (Which perhaps, may be partially absent in this case).

Cheers

[avandonk]

There are only questions and any good answers lead to more better questions.

If at any point one becomes smug and think one has all the answers one is doomed to mediocrity! This is known as dogma.

Bert

[CraigS]

Sure Bert !
Bring on the answers that lead to the better questions, I say !

Cheers

[renormalised]

Precisely.....how can you explain something properly if the basics of understanding for the subject in question is missing from one or more of the parties involved. That's why scientists have such a hard time trying to get information across to the public. By dumbing things down, you lose much of the meaning of what you're trying to convey.

It's also precisely why pseudoscience and other nonsense has the foothold it has and why the public don't trust what scientists say. Most just don't want to understand it (too lazy, not really interested etc).

I've tried to explain lots of things to do with science to many people. Only to have blank stares in return...even after dumbing things down.

[CraigS]

Yep .. its a major issue which inhibits effective communication, alright.

I think I'd rather wrangle with someone who is honest and comes right out and says: "I don't believe in Big Bang Theory" or "I don't believe in cosmological redshift", etc.

I'd always come back to my applicable principle, (which is out there for all to see), which is "you can believe whatever you like .. just don't let it get in the way of what's real".

The other issue here is about the role of scientific Theory in explaining independently verifiable, objective measurement. The two can be separated (and should be). We should not fear tackling the explanation (the theory part).

For me, as long as the theory is internally consistent (and testable), I'm satisfied.

It may not be so for others, however.

Cheers

[renormalised]

All too often!!!.



That's good...but how often do people just do that out of ignorance and can't explain why or have some lame reason as to why. Most can't back up their assertions.



A good principle, but most wouldn't subscribe to it. Nor would most let reality get in the way of their beliefs. Their beliefs are usually the things which are real to them, and the real facts become the nonsense. That's why things get so messed up.



No one should fear any part of the process, theory or observation. But many get the two confused and most would rather run in the other direction concerning theory.

[CraigS]

Gotta let 'em, try though … it is very rare that an alternative theory which is internally self-consistent, testable (and independently verifiable), arises in amateur science forums.
This does not mean that one can't arise, though.


The communication is difficult but it must still be possible.

Cheers

[renormalised]

Of course, they have every right to try. But like you said, it doesn't mean they're onto something. Even if they think they are and keep deluding themselves by dogmatically holding onto it.

People tend to invest too much personal worth in ideas. That's what gets them into trouble. An idea is just that...an idea, nothing more or less.

[xelasnave]

Come on you guys I developed my hypothisis of everything here:lol::lol::lol:
I do think it would be a difficult task to pull down the big bang theory or anything we take as established science but we still could be wrong...and no matter how small the probability we cant rule out that probability irrespective of the overpowering evidence that may suggest otherwise. That is still not saying we are wrong but that we should never think we are "infinitely" correct.
I neither believe in the big bang or disbelieve. I find it difficult to think humans could know it all however... I do know I will never know exactly how the Universe came into being but enjoy learning of how our science interprets their observations to date

alex

[sjastro]

Don't hold your breath Craig.

This is all new territory for him, he is now in a situation of having to defend his position by demonstrating a knowledge and understanding of the subject.

The troll tactic of attacking an individual's integrity to convey the impression of having that knowledge and understanding has been well and truly exposed for what it is.

Regards

Steven

[renormalised]

Something he's been trying very hard to do and succeeding rather badly in the attempt. He can't even recognise the difference between his own question and Craig's original.

[bojan]

The popularisation (explaining) of science in layman's terms is a science (and/or art) in it's own right.
Only a few people are good at it, most are not.

[Archy]

In reply to your statements:


My question was how can the "redshift" of a single photon be measured? So Bojan's response was the only relevant one and had everything to do with my initial and subsequent inquiries.

Your reply and Bojan's can't both be correct.
Redshift is measured from a spectrum. A single photon is not a spectrum of photons.

[Archy]

You are looking at your reflection in a mirror

All I asked was how can the "redshift" of a single photon be measured?

Only Bojan addressed that question squarely

[CraigS]

… deep ...

[sjastro]

Still waiting, waiting, waiting.......

[renormalised]

I'll put this in plain and simple terms so that even you can understand....a redshift doesn't need a spectrum in order to be measured. A spectrum is just the visible manifestation of the light passing through a spectrograph, or a prism, and can be used to observe and calculate a redshift. It can be just as easily done with any other instrument that detects light, so long as you know the method to do the necessary calculations and you have reference sources (which you need for spectra/spectrographs in any case) to compare to.

The redshift of a single photon can be measured if...1. The source of the photon is known (which I have reiterated about half a dozen times), and, 2. You can calculate or measure its observed wavelength/frequency.

The equations for calculating redshift are very simple, whether you calculate the redshift based on wavelength and/or frequency, or use the various relativistic calculations for z for those situations where it is used.

If you don't know what the source of the photon is, then measuring its redshift is impossible (which is what Bojan said in his answer).

Both our answers are correct, depending on the circumstance in which the photon is measured.

I have pretty much repeated myself several times in answering your question and so have some others here. I am not going to do it again. If you can't understand it even after this, then I suggest you don't bother trying.

[renormalised]

Oh funny boy:rolleyes:

You have been told this several times, repeatedly, the same answer. My previous post is the last you're going to get.

Oh, BTW....how about answering Steven's question about the relevance of your question regarding cosmological redshift and relativity...which is what this post was originally about. I'd like to see the answer to that as well.

[sjastro]

Let's look at this from his point of view. He is in a no win situation.

I have issued him with a challenge. In reality I have called his bluff.
If he refuses, it simply confirms he is a troll.

If he accepts, the onus is on him to explain mathematically the relevance of his question on relativity and the cosmological model.

Why explain it mathematically you may ask.
Firstly for someone who apparently is qualified enough to judge that a scientific statement "is beating around the bush" or constantly uses the phrase "is this the best you can do" must be in possession of considerable mathematical skills.
Secondly the use of mathematics minimizes the human or BS element.

Regards

Steven

[renormalised]

Not only considerable mathematical skills, but a very good grounding in the theory as well, Steven. He would have far more experience in the field than we would, if you go by his bravado.

[xelasnave]

While we await a responce...
I have been taking in what I can and ask although we see a photon as a descrete object is there any view of it as made up of many other smaller er bits.
And does a photon only cover the visual range of the electromagnetic spectrum.
alex:):):)

[CraigS]

The photon is an elementary particle.

It also describes the abstract carriage of the electromagnetic force. As such, it also covers the full range of the EM spectrum .. not just the visible.

Cheers

[sally1jack]

seem's to be degrading again , the behavior is very similar to my children, so disappointing to see this happening.
Carl ( renormmalise) i read in one of your post a while ago that when people behave in this way you just don't reply, what happened to that ? not that i disagree with you i think you explained your point & i understood it.
if this is the way the wider scientific comminity debate things then progress will be at a snails pace
there are a group of regular contributors with a good knowledge base which i enjoy reading & have learned from them which i appreciate. but what disturbs me is when a contributor ruffles there feathers they gang up & attack this is not to say that there scientific point of view was wrong, but its the way it is done
To have superior knowledge or intelligence gives know one the right to belittle someone or name call like "troll"
I think the moderators should be firmer on personal attacks which both sides are firmly guilty of
I see & understand that strict scientic principals are abided by to ensure good scientific debate , strict ethical guidelines here are lacking.
I see fewer & fewer people contributing i believe that this behavior can't be helping this

hope this improves

[CraigS]

Hi Phil;
Good to have your input.
We tried to get some principles in place a while ago … until someone formalises something, all we can do, is what we can do, as the need arises.
Overall, I agree with where you're coming from.

Cheers

[CraigS]

Frankly, I see several categories of discussion running simultaneously which adds to the confusion:
i) Questions/answers to 'bread & butter' mainstream science;
ii) Research update discussions on mainstream topics;
iii) Proving ground discussions for those wishing to develop their 'ideas' (non mainstream).

Love to see 'em separated !

Cheers

[sally1jack]

Hi Craig, i disagree this is a matter of respect , if a contributor shows disrespect to an individual or the principal at hand then we shouldn't get down in the mud a play dirty as well .
If people started reading some of these threads i don't think that they would think to themselves that this is a quality ethical site for science, we don't need guidelines we need ethics & manners or this forum will continue to deteriate like other forums have which is a joke. we are all adults here lets share knowledge& respect each other.
Craig As one of the regular contributors i feel that you have an obligation to conduct debate in the proper manner, don't feel like i am singling you out as i think that you do this better than most,
this should be about science not emotion
ive had my say & i'll go back under my rock

Phil

[renormalised]

I give people a number of chances. If after that, they are still carrying on like numpkins, I just don't bother anymore. Which is what I've told this person in particular. He's not getting another answer off me and I don't particularly care what he asks in the future. He's on his own.

Fewer and fewer people contribute because of idiots that come on and try to disrupt everything for everyone. They're not here to find out anything, they're just here to troll for trouble or to hear themselves talk. If it wasn't for proper decorum and the rules of the forum, I'd be telling them to bugger off in no uncertain terms. Anyone who carried on like that in any talk or lecture I've ever given would've been shown the door very smartly. Most of them have chips on their shoulders and are not willing to listen whatsoever to anything anyone says. They don't want to learn or understand, so they just keep carrying on until something gives.

I also think that before you, or anyone else chips in with an opinion on this matter, you take a good look at what's going on. I would imagine that if after repeating yourselves several times with no obvious progress and then being berated by the person in question and having your explanations disregarded flippantly, you be a little more than peeved or defensive. Quite frankly, if Steven, myself or anyone else here is going to be treated like this for too much longer, we just won't bother with even posting in this section at all. Why should we go out of our way to explain things to anyone, only to have our explanations thrown back in our faces and told we don't know what we're on about...which is what has happened in this case and others, in the past.

I'm glad that you and many others appreciate what we have to contribute to this forum, I'm happy to give of what I know. But, I can tell you now that if the sort of nonsense that has happened in this case and others keeps up, I will just walk away from it and not even bother. I'm getting a little sick and tired of putting up with fools who just come in here and want to disrupt the good nature of this forum and cause confrontation or just won't listen to anything anyone says. If they're that knowledgeable to begin with, why even bother asking the questions they do...let's hear what they have to say. They should be teaching/explaining things to us, not the other way around. Quite frankly, they're full of it and I'm not putting up with it. I doubt any of the others are, either.

[CraigS]

Make some constructive suggestions for how to structure future conversations Phil.
The issue I see in this one, is that we have two entirely different levels of science conversation .. the one I started and, the one Archy is attempting to promote. There'd be no angst if that was recognised. (Some recognition of that by Archy would help).

Cheers

[renormalised]

Phil, normally the wider scientific community has debates which are well conducted and for the most part the participants respect one another.

However, don't ever think that really heated debates and even all out barneys don't occur. Even in debates where things are generally done in a respectful and proper manner (for the most part) there can be some rather heated situations.

[renormalised]

The ToS gives those outlines as best as it can. And the heading of this forum gives a generalised outline as to what should or shouldn't be in here.

It's not so much different levels of conversation as it's to do with giving of the proper respect to those who do contribute to this forum and who have the knowledge to make meaningful contributions without them, or the people asking questions they want answered, being disrupted and castigated by people who have no intention of either learning off anyone who makes a contribution or is just out to stir up discord amongst the forum members.

[sjastro]

Looking at this thread is only a snapshot of an issue that goes back 2-3 years.
"Not playing in the mud" has failed miserably in the past. In fact I have no doubts it has encouraged the individual to carry on the way he has.

Using the Science forum to engage in gutter level personal attacks against individuals simply because he resents a display of knowledge is the issue here.

I think a lot worse terms than troll.

Steven

[CraigS]

Not good enough for rigorous Science forum discussions, in my view.

This forum will be forever doomed !

Cheers

[sally1jack]

Look Carl im not having a go at you . i am grateful for your & other imput & would be sorry if you stopped contributing,
you can't & won't stop people from being how they are , i believe if ther is a sensible debate performed correctly then the idiots will fade away & even if they dont who cares, people will listen & believe what they want
but when we start to degrade the debate then we can't complain
You contribute here for a reason & thats your reason , to stop because someone is aggrivating you is a llitle selfish if you have great knowledge then you should share it because someone taught you & if they took the same line then knowledge would stop being learnt by all
Don't take this personally carl as i don't know you & am not judging you but i think we need to be above all this crap & continue to debate reguardless of the disrupters
hope you continue
phil

[renormalised]

Craig, this forum is not a formal debating society. Nor is it a open ended scientific conference. If you try and impose those sorts of rules on this forum, you'll lose the whole character of the forum and people will just not bother to post here.

[CraigS]

Man, this perception really bugs me … its kind of a latent assumption !

Unless I'm mistaken, no-one here is under ANY obligations to share anything !

The 'lurkers' here are doing exactly this (ie: NOT sharing) .. and when the going gets tough, somehow contributors are held accountable to them ???

What poppycock !

If someone wants to walk .. then that's their decision … and theirs alone !

Cheers

[CraigS]

That's happening anyway, Carl.

It can't get much worse !

[renormalised]

I know you're not having a go at me, per se. This forum is normally conducted rather well and everyone gets along just fine. However, just because you conduct something in a proper manner doesn't mean that those wanting to disrupt everything are going to just fade away. They will keep coming along regardless of whatever you do.

Why should I, or anyone else have to put up with being aggravated or repeatedly told we don't know what we're on about, or questioned for no good reason by people who it's plainly obvious are only here to stir up trouble or just want to act like ignoramuses. After awhile, you get sick of it. If it keeps up, you just remove yourself from the scene and stop posting....there's nothing selfish in that at all. I've done it before on a number of occasions, especially since I had rather more important things to do than waste my time arguing with fools who didn't want to listen. All you do with these people, after a fair number of tries, is just waste your breath and effort even bothering to reply to them.

If I had've carried on like some here have at any of my classes at uni, I'd have eventually been booted out the courses I took. That would be guaranteed.

[renormalised]

Got a point there:)

[sally1jack]

craig i didn't say that anyone here is under obligation to share anything, if you dont want to thats fine , but you guys do & all i was saying is to stop because someone is having a go at you is not a good reason to stop
phil

[renormalised]

What would you do if someone kept getting in your face and being confrontational. I'd hazard a guess you'd either walk away from it or push back (until you had enough and then walked away, anyway). If they pushed you far enough, it might even come to blows.

Phil, let this present conversation lie, OK. It's only going to cause more discord and it's so far off topic anyway, it's become a farce.

I'm not here to argue the finer points of my own actions and what I do is entirely up to me. Same for anyone else. Let this be the end of the matter and move on. I've had enough of arguing about semantics for one day.

[CraigS]

Yeah fair enough Phil, but I really don't think onlookers appreciate how much emotional effort is required to uphold a rigorous, unintuitive line of argument in these debates.

This was my point here.

I refuse to held accountable to onlookers who jump in when the going gets tough with their low-value opinions, on what they see. If these types wish to be acknowledged, then let them get involved in the debate and experience what there is to be experienced .. this is the only way they'll ever earn my respect.

Cheers

[renormalised]

Precisely, Craig.

It takes a lot out of you when you go on with constructing arguments and counterpoints to debates. All that thinking burns up the calories!!!!:):):P Especially when everything is coming from first principles, straight from the top of your head and from your own learning/experience. Even trying to find references can get tiresome, especially if you're having to back things up on the fly, which is damn near impossible unless you've looked into the topic in question before you or others have posted it.

And if you're anything like me, you'll have journal articles and such scattered everywhere and in all sorts of files!!!!:):P

[CraigS]

Once we surmount all this noise, I have been patiently waiting to extend my initial discussion, so that we can venture into a discussion on the closely related, special relativity time dilation due to aberration topic.

Until we get over Archy's issues though, this seems futile. :question:

Cheers

[sjastro]

Oh dear this one open to an argument.:lol:

[sally1jack]

[QUOTE=CraigS;745670]Yeah fair enough Phil, but I really don't think onlookers appreciate how much emotional effort is required to uphold a rigorous, unintuitive line of argument in these debates.

I have thought of that a few times Craig the number of times you post would make it difficult to do other things , do you work ?
phil

[renormalised]

Yep....Archy's aberration has had it's time dilated and is not all that particularly special to the original discussion, relatively speaking:):P

[xelasnave]

Thanks Craig. I read something suggesting it applied outside visible range and realised I had somehow only thought of it as within or close to the visable spectrum..

alex

[CraigS]

Not sure if this'll work, but the question is, can someone explain what this gif is showing?

The original link is here (http://en.wikipedia.org/wiki/Electromagnetic_wave_equation#Covar iant_form_of_the_homogeneous_wave_e quation) (if the gif upload doesn't work).

Cheers

[renormalised]

Click on the gif in the article, there's an explanation as to what's going on there in the gif's description.

What the gif is explaining is that the velocity of light is a constant from either fleets perspective (communication between the ships), but that the apparent paths taken by the light beams from the perspective of the opposite fleet appears to take a diagonal path between the ships at a time which is also apparently longer than the actual communication time between the ships. The effect of time dilation in transverse motion. All due to the relative motion (inertial frames of reference) between the two fleets.

[sjastro]

It's how you explain the reality of time dilation as an exercise in aberration.
You have a photon bouncing between two mirrors.
If the observer is stationary relative to the mirrors or the mirrors and the observer are moving at the same velocity, the observer will see photon hitting the surface of the mirrors at a 90 degree angle. The distance travelled by the photon from one mirror to the next is simply the spacing between the mirrors.

Suppose the observer is moving relative to the mirrors in a direction perpendicular to the direction of the photon in the rest frame. The observer moves a certain distance in the time it takes photon to travel from one mirror to the other. The observer therefore sees an oblique photon path instead of the photon path being perpendicular to the mirrors in the rest frame.
As the photon path is now oblique, the distance travelled by the photon is also longer. Since the speed of light is the same to all observers, the time taken for the photon to cross the mirrors relative to the moving observer is longer when compared to a stationary observer.

Note this form of time dilation is not directly related to cosmological time dilation.

Regards

Steven

[CraigS]

Ok .. thanks folks …
:)

:lol: ;)

So then, this all is underpinned by this ... (http://www.youtube.com/watch?v=XavC4w_Y9b8&feature=related)
(one of the seemingly most misunderstood experiments by certain folk, second only to the Sagnac Effect) ...

and then to this ... (http://www.youtube.com/watch?v=A2-cRhk76TY&NR=1)

(Just had to do this, so I could record the excellent YouTubes).

Cheers

[sjastro]

At cosmological distances objects are accelerating away from the observer.
Hence we are not dealing with an inertial frame of reference.
Under these conditions SR (Lorentz) time dilation is not applicable.
Time dilation at cosmological distances is handled by the R-W metric.

Regards

Steven

[renormalised]

Precisely, using the equation....

1+z=A(now)/A(then)

A being the cosmological scale factor. Now being at present and then being at some time in the past.

[CraigS]

Right. So, in summary we have (I hope):

i) the "blinking out phenomenon" is explained by cosmological redshift, which is encapsulated in the R-W (FLRW) Metric solution, which is an accelerating universe model;

ii) the event horizon for a BH is based on gravitational redshift, as is time dilation within the grav. well;

iii) Lorentz time dilation is applicable for objects moving with respect to an inertial observation reference frame (eg: constantly expanding universe models, as distinct from acceleratingly expanding models);

iv) the Michelson Morley experiment (MMX) was designed to prove a cosmological aether, but resulted in disproof of a cosmological aether;

v) the results of the MMX experiment were eventually explained by Lorentz contraction/dilation, and was wrapped into special relativity.

I hope this is OK ?

Cheers

[sjastro]

When you apply Einstein's field equations with the cosmological constant to the R-W metric, you get a set of equations known as the Friedmann equations (http://en.wikipedia.org/wiki/Friedmann_equations). The solutions provides various parameters for the Cosmological model for an accelerating Universe that includes the geometry of the Universe, a time dependant Hubble "Constant", density, pressure, etc.



Correct



No. It doesn't apply to a constantly expanding Universe as the Universe is still accelerating in the observer's frame of reference. Einstein's field equations without the cosmological constant term is applied to the R-W metric. The R-W metric is consistent with a constant expanding Universe.



Correct.



Lorentz attempted to explain the MMX experiment by an ad hoc use of the Lorentz transformations but under the assumption that aether existed.
Einstein on the other hand mathematically derived the Lorentz transformation under the assumption that aether did not exist.

Regards

Steven

[renormalised]

The R-W metric is a solution to Einstein's field equations within a homogenous and isotropic spacetime which is either expanding or contracting. It's not necessarily an accelerating universe.

The EH for a BH is defined by the equation...

Rs = 2GM/c^2, where G is the gravitational constant and M the mass of the object. Rs is the Schwartzchild radius. You can work it out with gravitational redshift as part of the equation for this contains part of the derivation of the Schwarzchild metric...2GM/C^2r...where...

1+z= SQRT((1-(2GM/c^2 Rr)/1-(2GM/c^2 Rs))). R is analogous to the radius of the object or the radial coordinate of the source (the point on the surface of the sphere defining the radius from the centre. Or in this case, the distance from the receiver/detector (r) to the source (s)).

Lorentz time dilation occurs in flat (Minkowski) spacetimes in reference to the relative inertial frames of the objects in question. It's essentially relativistic doppler shift.

[Archy]

We have both stated our views on the question of redshift. You say you it can be calculated if you know the source, and I maintain that it cannot be determined in the absence of a spectrum, which a single photon is not. However, redshift is irrelevant to your original question the gist of which is:



For the cosmological model postulated by CraigS it is possible the the two galaxies will blink out at the same time.

However, the entire universe can only blink out if Y is a photon from the galaxy furthest from us and X is a photon from the galaxy nearest to us and all galaxies are receding so fast that light cannot reach us. However some galaxies are not moving away from us. So the universe will not blink out all at once.

Further, CraigS did not stipulate that Y is a photon from the galaxy furthest from us and X is a photon from the galaxy nearest to us. So the question as stated was flawed.

[sjastro]

This is clearly not correct. It violates Hubble's Law which states the recession velocity is a function of the proper distance of the galaxy to the observer. If galaxy Y has "just" blinked out it has done so because it has exited the Hubble sphere. Galaxy X which is closer to the observer is still inside the sphere and is therefore still observable.
This is applicable if galaxies X and Y are formed during a period when the acceleration of the Universe began and the expansion of the Universe is faster than the expansion of the Hubble sphere.
If on the other hand galaxies were formed during a period when the expansion of the early Universe may have been slightly decelerating, the Hubble sphere can expand faster than the expansion of the Universe. In this case those galaxies that are just beyond the Hubble sphere will eventually become visible. So we will never achieve a total and sudden blink out even if all galaxies were receding.



I must be missing something here. Photon Y is assumed to be emitted from galaxy Y and photon X is assumed to be emitted from galaxy X. Craig has clearly stipulated that galaxy X is closer than galaxy Y.

[renormalised]

Well answered, Steven. Let's see if he argues with this.

His explanation makes no sense, let alone being theoretically and empirically incorrect.

[CraigS]

!!!!
:eyepop:

[renormalised]

More like....:rolleyes::rolleyes:

Armchair "expert". Not a clue at all.

[Archy]

You seem to have problems with: However some galaxies are not moving away from us. So the universe will not blink out all at once.

The Andromeda galaxy is not moving away but towards us.

[Archy]

What is clearly incorrect:
1) For the cosmological model postulated by CraigS it is possible the the two galaxies will blink out at the same time.

2) However, the entire universe can only blink out if Y is a photon from the galaxy furthest from us and X is a photon from the galaxy nearest to us and all galaxies are receding so fast that light cannot reach us.

3) However some galaxies are not moving away from us. So the universe will not blink out all at once.

You mention the Hubble sphere. As I understand Hubble sphere is the region of the Universe (http://en.wikipedia.org/wiki/Universe) surrounding an observer beyond which objects recede from the observer at a rate greater than the speed of light (http://en.wikipedia.org/wiki/Speed_of_light), due to the expansion of the Universe.

There has been no empirical evidence of anything moving at a rate greater than the speed of light (http://en.wikipedia.org/wiki/Speed_of_light).

[Archy]

Where does it not accord with theory.
Where is it empirically incorrect

[renormalised]

Just for you...go and reread this part of your answer. If you don't know why your answer doesn't make sense, then there's no point in me trying to explain it to you.

While you're at it....what makes you so eminently qualified to dismiss our answers offhand??.

[sjastro]

Try re-reading my previous post.



Of course there is empirical evidence. Any object that has a cosmological redshift z> 1.46 has a recessional velocity greater than c.
The reason we see some of the photons emitted was explained in my previous post.
Objects formed in this era occurred at a time before there was an acceleration in the expansion of the Universe. Photons that are intially superluminal become subluminal as the velocity of the Hubble sphere can eventually exceed the scale velocity of the Universe. These subluminal photons become observable.The objects themselves however continue to recede at superluminal velocities.

For a more technical explanation.
http://arxiv.org/abs/astro-ph/0310808

The Wikipedia article regarding the speed of light refers to objects travelling in space-time. When we refer to recessional velocities of objects, the objects are in fact stationary in space-time but are being carried by the Hubble flow or the expansion of space-time.

The Wikipedia article has no relevance.

[renormalised]

You know the stupid thing here, Steven. He states "what is clearly incorrect" and then mentions 3 points that he says are incorrect. It's funny how those same ones he states as incorrect are exactly the same points he used to try and prove his position, in an earlier post.

If that's not a case of contradicting one's self, then I don't know what is:P

[sjastro]

Initially I was totally confused.:shrug:

Regards

Steven

[renormalised]

Considering his poor style and inconsistent logic, that wouldn't be hard to understand.

[CraigS]

Sorry George .. I have a few higher priority matters to deal with over the next week or so, and I will be offline for that period … Steven has already answered your issues about this matter a few times anyway.

Cheers

[renormalised]

A prime example of not understanding the science behind the question.

Why do you suppose M31 is not moving away from us within the general Hubble flow.

If you do know the science, you will know the answer.

[marki]

Carl just put him on your "ignor posts by" list. Much easier and less stress.

Mark

[sjastro]

For any masochists out there who fancy an intellectual challenge here is the 156 page PhD thesis on which the above abstract is based on.
http://www.physics.uq.edu.au/download/tamarad/papers/thesis_complete.pdf

Enjoy :P:lol:

Steven

[renormalised]

I accept the challenge:):P:P

If you don't see me in here from now on, it's most likely because I've gone wacko after reading this thesis:):P

[renormalised]

Good paper.....easy to understand, but hard to read when you keep nodding off like I have been!!!:):P

Have to reread it:)

[Archy]

Blather, but not an answer

[Archy]

Thanks for exposing what is wrong with your concept of the universe

[Archy]

Don't misquote me I asked which of the three points were incorrect, not that the were incorrect.
It it that are you trying a debating trick of misquoting to avoid giving an answer?

[sjastro]

Don't insult the intelligence of forum members by implying you have a comprehension of what is going on.

PS.

"Is this the best you can do."

[sjastro]

Go learn the definition of obfuscation because that is what you excel at.

[marki]

Dont feed the troll :P

Mark

[renormalised]

Oh boy...



That is what you wrote. If you seem to think that is a question, then you don't even know how to construct a simple sentence asking one. This paragraph you wrote clearly states that these three points are clearly incorrect. And you accuse me of misquoting you!!!. You can't even quote yourself correctly!!!!. Several posts before the said post that particular paragraph was in, you use exactly the same points to try and prove your own position. A blind man could see that was completely contradictory and eminent proof of your complete lack of understanding of the subject in question.

Then you had the hide to bombastically accuse Steven of being complete wrong about his concept of the Universe. I doubt you even bothered to read the journal articles that he posted. As a matter of fact, it would be a 100% certainty that you wouldn't even understand anything that was being said in those articles. It wasn't Steven's concept of the Universe you're questioning and saying is wrong. It is the theoretically and empirically accepted view of the Universe by the vast majority of the entire scientific community that you are saying is wrong. Are you trying to tell us here that you know better than all those scientists, and they include myself and Steven. So, instead of accusing me of blathering, as you say...



how about actually being honest here and answering my question....



Let's see if you can be honest with us, but more importantly with yourself, and answer the question.

The only person that is blathering here is you. We have repeatedly answered your questions only to have you completely ignore them and then for you to go on and attack our positions. We gave you plenty of chances to listen, even repeating ourselves several times in order for you to pickup what we were trying to get across to you. But all we've got is prattling nonsense in return.

Know what, I'm not going to continue on here. All I'm doing is wasting my breath on someone who isn't worth the effort.

Stop wasting our time here, posting. You're in way over your head and with your attitude, none of us here will even bother to answer you from now on.

[avandonk]

Can anyone explain to what my mobile phone is doing? It seems to have a life of it's own.

I bought it with the expectation of being able to make phone calls not some text message that tells me I am making a phone call!

Are the same dimwits who do not understand science now in control of my phone for some dubious marketing exercise?

All answers will automatically be sent to my phone.

Bert

[renormalised]

It's a message from another time and parallel universe, Bert. Somehow tunneled its way across the barrier. It's from Universe "Dimwit", where all the 2012, EU and other wastes of time reside:):P

Best to just shove it back down the wormhole:):P