The life of 'Light'

[ballaratdragons]

I have, for many years, pondered the issue of 'when does light run out'?

Light itself must be an amazing thing as it appears to never diminish . . . or does it?

We look up at the Heavens with our unaided eye and see up to billions of years into the past, and even further with our Telescopes!! Our cameras catch light even further back in time and distance!!!!!!

OK, here's the thing: Light left a star billions of years ago, travelled for those billions of years, over multiple-trillions of kilometres, and is still shining bright!

When does 'light' actually wear out?
It MUST eventually.
If so, what else is out there that we are not quite seeing that has faded due to time and distance.

[[1ponders]]

As I understand it Ken (and I may have misremembered it as Uni Physics was about 30 odd years ago), light does "wear out" but doesn't disappear. From what I understand, as light propagates through space (ignoring the reddening effect of dust and gas) it uses up energy. This lost energy reduces the frequency of the light. So if the light at a galaxy on one side of the universe started out as blue, at some point it will become red and then invisible to us as infared and then as radio waves. I don't know the distances and time frames involved but they are considerable.

This is different from the doppler shift of light.

[ballaratdragons]

Thanks Paul,

but you would think at some stage it all wears out. It may take a trillion trillion years, but eventually :shrug:

[[1ponders]]

I guess the closest analogy I can give is the cosmic background radiation that started with the big bang. Its taken something like 15 billion years but the initial radiation is still there but only warm (3 degree Kelvin or somet such) enough to produce the faintest of microwave radiation.

[wasyoungonce]

now now boys in what medium does light propagate in space??:lol:

is it a wave or a particle:lol:

cannot have it both ways;)

[Kal]

This change of wavelength is due to the expansion of the universe, or something else? Reading up on CMB, for example, I come across this (http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiati on): " As the universe expands, the CMB photons are redshifted (http://en.wikipedia.org/wiki/Redshift), making the radiation's temperature inversely proportional (http://en.wikipedia.org/wiki/Inversely_proportional) to the Universe's scale length (http://en.wikipedia.org/wiki/Scale_factor_%28Universe%29)."

I would imagine all light to be redshifted by the act of the universe expanding, which could be construed as photons losing energy as they travel through space.

[ballaratdragons]

Eventually getting to Zero energy?

[Kal]

That depends on if the universe continually expands (open universe) or not. There is still (and I don't forsee an answer to this question any time soon!) alot of debate over whether we live in an open or closed universe.

[cahullian]

I don't think light runs out , I think it gets absorbed. If you are in a room with no windows or doors the light inside the room won't be seen from the outside as the walls absorb said light.
Just my layman term for something I have no understanding of.

Gazz

[robagar]

I guess for redshifted photons to have zero energy the wavelength would have to be infinite. That's never going to happen no matter how much spacetime is stretched by the cosmic expansion. Unless the expansion is infinite, in the "big rip" of some cosmological models perhaps?

[Paddy]

I'm with Gazz, also as a layman. If photons travel at the speed of light, doesn't that mean that they must have zero mass? And if so, doesn't that mean that they can travel without losing energy unless they are absorbed by something that they encounter on the way? And here I may really reveal my astronomical ignorance - don't even massive objects like planets continue through space without losing momentum unless they encounter another object? If all these are true, light would not run out unless it is caught out. I think. Grateful for education from the more knowledgeable

Patrick

[robagar]

You certainly can't accelerate a non-zero mass to the speed of light, so yes I *think* it means you can say that anything going at light speed must be massless.

Another way of looking at it is this: if a photon can disappear without hitting anything else, then it must have a finite lifetime. But the time dilation effect at light speed is infinite, so we could never see it happen. Therefore photons must live forever :)

[Paddy]

Thanks Rob, that second last sentence in particular will give me something to contemplate!

[robagar]

Relativity's good like that :D

[janoskiss]

Light does not "run out" or change its characteristics as it travels through space. However space is not empty so it will eventually interact with something and lose some or all of its energy in the process.

For example, each photon that makes up the light you see through your telescope has traveled millions of years to be finally extinguished as it hits the back of your eye, where its energy is released to induce a conformational change in one of the many millions of rhodopsin molecules in the retina, which in turn causes transfer of charge - a single proton - that sends and electrical signal up the optic nerve to the visual cortex which triggers a whole series of neural impulses in the brain to manifest to you as the conscious awareness of seeing starlight.

Here is a trippy thing: in the photons frame of reference there is no passage of time because light is travelling at the speed of light where time slows to a halt. As far as the photon is concerned its creation in the nuclear fusion inside the star, its long journey to you, and its annihilation in your retina all happened in the same instance. Its only in your frame of reference that many millions of years had passed.

[Paddy]

It is indeed an extraordinary thing! I have just come in from some stargazing under a beautiful clear dark sky. As I was observing NGC 1097 I reflected on your comment that the photons that have traveled 40 million years to enter my eye and become part of my experience would themselves have done the trip in one instant. Quite a koan really.

[ballaratdragons]

Hmmm, thanks for the explanation Steve, and believe it or not it all made sense to me.

Pity we can't turn a spaceship into photons and send it off at 'light' speed. If light photons travel at light speed so would whatever was transformed into photons. The trick would be converting it back into a spaceship.

Bit Star Trekkish, but they refer to a different form of 'Beaming up'.

[Paddy]

If, from the point of view of the photon, no time has passed between its emission at light speed and its absorption, does this mean that, again from its frame of reference, it never existed? Even though it would have existed from the perspective of the observer.

[Kal]

Light is really just energy travelling through space in discrete amounts. We see the results of this energy, but we don't see it by itself. In fact, we can't even say where a photon is with certainty, we can only state a probability of where it will be.

Consider throwing a rock. The energy was transferred from your body to the rock, but does the energy really exist from it's frame of reference? Light is similar to this, except instead of a rock it is travelling in what we call a photon, and instead of going faster if I throw it with more energy, it will travel at the same speed but it will have a different wavelength.

[robagar]

Not sure if the photon's frame of reference is valid in any case - after all, the basis of Special Relativity is the idea that light goes at c in *all* inertial frames.

[JimmyH155]

I read quite recently that they cant make up their minds if light is a wave or a particle. (as you ask, wasyoungonce:))
I think it sometimes acts as both. What really blows my mind is Pauli's exclusion principle concerning orbiting electrons, and Heisenberg's uncertainty principle that says a photon can be in two places at the same time:D. Wish I could be like that:rofl:

[wasyoungonce]

Sir William Henry Bragg, with the following quote:

"Physicists use the wave theory on Mondays, Wednesdays, and Fridays, and the particle theory on Tuesdays, Thursdays, and Saturdays."

Which was often recalled as:

"On Mondays, Wednesdays, and Fridays, light behaves like waves, on Tuesdays, Thursdays, and Saturdays. like particles, and like nothing on Sundays"


meeh! It's an EM wave for radio and double diffraction slit experiments but a particle of the photoelectric effect.:lol:

[KenGee]

Photons are the are particles they only behave like waveforms when your not measuring their location. Lights wave like behaviour is an excellent way to demonstrate Heisenberg's uncertainty principle. Amazingly you can see the uncertainty of the photons location manifest itself as a interference pattern during the famous double slit experiment. But this is were it gets stranger photons can actually be a collection of quarks and gluons!:help:

[wasyoungonce]

Possibly light is a combination of Quarks (and anti-particles)?...the building blocks of all subatomic particles.

But there are also Leptons and Bosons....

Bosons are thought to be the carriers of fundemental forces (gravitation, weak and strong nuclear forces, electromagnetic).

After all light as an EM wave has an electromagnetic component at 90 degrees to it's wave ...it can be polarized removing this force. thus it must have Bosons at work?

It gets even stranger.....:whistle:

[xelasnave]

Whatever way we try to understand light it is indeed extrodinary that it seems to last forever.

How the energy is managed I have no idea..but how strange that we are able to "recieve" light as evidenced in some of the Hubble captures of light billions of years old..even if that light does not know it is that old:D...

I have read that if one calculates the "heating" effect of all the star light one will get a figure the same as that of the background radiation..I dont know what presumably overturned this idea..other than it did not suit the big bang theory.

alex

[higginsdj]

Well actually the interaction of light with other matter just means that the light is re-radiated at another wavelength (ie dust absorbs the energy from a photon then re-radiates it at IR with the same amount of energy) or the light is reflected/scattered. It all depends on what you mean by light losing energy....

Cheers

[higginsdj]

Well there is one big flaw in that theory. It would imply the the CMB should be hotter (at the CBM wavelength) in the location of nearby stars, including our own sun!

Cheers

[xelasnave]

Thank you David.

I imagine however that when doing the calculations the heat of the Sun is subtracted and given the small numbers they work with...and the contrast in the temprature of the Sun's region and the Background radiation temp...I do not think such evidence would be conclusive... however I do not mean to start anything on this as I simply do not know enough to hold any position.

I did find some work had been done by a certain University in the Southern USA which showed problems with background radiation "shadows" however I strongly feel "they" had a leaning to establish the big bang as questionable... and given their funding and board may well have strong Christian connections I felt they may have had a particular result in mind..the result they came up with that is.

Background radiation is perhaps the strongest key stone to the big bang theory (in my view) and certainly is cited as absolute proof by many... not saying they are wrong but to a layman like me I find the establishment of the big bang notion based on data so minute in variation difficult to accept without leaving questions in my mind that there could well be other explanations.

I was distrubed to read an old magazine showing pictures of computer models of how they expectedto find background radiation and that these models show little variation form the final map (to my untrained eye) that raised in my mind the possibility that they found exactly what they had hoped they would find... reasonable no doubt... but I am a suspicious person and frankly that is what got me thinking more about the exclusion of alternatives to the main evidence offerred for the theory.

I am somewhat cursed that I believe little and trust no one leaving me somewhat without any beliefs or strong positons I am prepared to defend.

Thanks for pointing out your point I really do appreciate it:thumbsup:.
alex:):)

[higginsdj]

HI Alex,

I have just completed the Galaxy and Cosmos unit at Swinburne as part of my graduate certificate and it is well established that the BB theory has problems. The only reason it is still there is that there is no other theory that fits all the observational evidence (or even comes close) - but there is certainly no proof.

The other side of the coin is that Cosmology is being questioned as an actual science (not the observational side - just the theory. There was an interesting paper published on the matter which many observational cosmologists revisit every now and then to put it all into perspective.

What I do find interesting is that there are 'scientific' groups out there who try to re-interpret the observational evidence in an effort to discredit the BB theory rather than trying to find an alternative theory. Without an adequate alternative theory the best they can hope to achieve is to have the BB theory modified.... but I fear we are getting off the original subject of this thread :)

Cheers

[xelasnave]

Yes David threads I get involved with sometimes get off track.
I think the problem with BB is everything is found to support it and nothing else, as far as mainstream is concerned...still I take your point one can not rip up the house plans if there are no others.
I see no reason why a steady state theory had to be thrown out.could it not be adjusted in the same manner that BB gets adjusted....but if the BB were subjected to a similar approach to BB it would be thrown out also.
So in that context I suggest that there may well be an alternative..an infinite Universe makes more sense than a Universe with a start ... BB fits human experience and expectations and for me the parallel between the creation seen by the church and creation seen by BB seems more than a unbiased coincidence...
However an infinite Universe needs no start and will be at odds with human expectation and experience... the Universe may not experience the same limitations we would place upon it from our human experience.

I am always having a go at the big bang because of its reliance on the inflation theory..a theory based upon a flawed view of virtual particles.. sticking to it simply means a better explanation will never be found..but as inflation is unfortunately accepted no other more reasonable theory comes into play...

Those defending the BB must do so but I think there is a refusal to consider what does not fit their picture... that is a view and could well be wrong but impressions form from many things and that is a "feel" that any reasonable person following the matter would form.

If one expects observations to fit what one believes in of course no other explanation will get a look in...

I dont care one way or the other but I have my doubts that alternatives get a reasonable airing in respect of observations... and when one finds NASA has a department to prove Dr A right one must wonder why would a department be needed for such a mission....

I do not know why science is behind such an approach but it reeks of a matter more related to funding than to science....and dont get me wrong Dr A is one of my heroes... and in respect for those who hold a hero to mean something greater and a term to be used only in respect of brave folk saving lives I ask that in this instant you grant me a little lee way on the use of the word so I can more on...but my point is I am not having a go at him but I feel that his approach may well suit the church as I feel BB offers a comfortable and similar parallel to creation.... an infinite Universe would seem at odds with the church I expect in their view but only because they seek to measure by human experience and expectation..I feel A God would exist in an infinite environment.
Observations will support the views of those making them I feel...I dont care how good the science it is carried out by men and men are always subject to corruption whether they are conscious of it or not...
Anyways I could go on and on but I must go.
If I can offer an alternative I will but see the benefit on working on a plan.. I dont like the way so many seek to destroy without an alternative and I agree on this however if something becomes unsupportable it must go even if there is nothing to replace it.
alex
.

[xelasnave]

I dont know if I covered the stuff hereunder because I was in such a hurry..but steady state got the axe because they found background radiation..or rather what they found was interpreted as background radiation such that it supported the BB.

So on only one point steady state was shown the door...what if the background radiation data has another explanation ..and given we are dealing with matters of difficult measurement and possible alternate explanation one wonders why what was found now has no other explainantion.

Today as I said there are some out there who are shooting holes in the premise of background radiation. I am equaly suspicious of their motives...but that is not the point really the point is why be so hasty in saying .."we have found background radiation..as the theory suggested we would..now there is no need to ever look at the steady state idea again..."

And when one recalls that it was the steady state theory that provided the footing to develope theories on the creation of elements within Suns it seems that only part of the idea was disgarded... the part that did not suit BB...

Now as I understand it prior to the development of the theory of element synthesis within stars the big bang followed the view that all elements were created at the moment of the big bang... so that seems like a case of we take the good bits and throw out the rest because it does not fit our theory... well I simply say this if the steady state theory could develope the now excepted notion of element synthesis within stars as oppossed to a creation at the point of BB how could one throw the steady state theory so fast.
Humans want a creation whether by religious or by scientific means but that does not mean the Universe agrees...An infinite Universe to me would fit better the notion of a God..presumably infinite.. and I have dificulty imagining a finite Universe floating in a sea of nothing and it expanding into that sea of nothing as the apparent observed expansion dictates. There can be something we call nothing.. empty space is not...nothing.
Space can not be finite one would think otherwise it must sit in "nothiong".

Sorry David to be in a rush and not give this matter the importance it deserves with expanded detail.

Sorry Ken for getting off track and also somewhat going against your views in other areas... but when you think about light one thinks about these related matters.

Sorry to all if spelling and English take the back seat here.

alex

[higginsdj]

Hi Alex,

There is much more observational evidence indicating the failure of the steady state theory other than just the CMB. The steady state theorists themselves (a la Fred Hoyle) told the BB crowd that if there was a BB then there would be evidence along the lines of the CMB. Years later - low and behold we discovered it.

Steady state theory indicates there there is a steady number of and taxonomy of objects in the universe - ie galaxies. Observation has shown that this is not the case. Galaxies in the early universe (BB timescale) are nothing like nearby 'modern' galaxies.

BB is NOT creation - BB is the start of expansion/gravity/dark energy/dark matter that led to the formation of stars and galaxies. Everything we are was already there. BB states that at the point of the BB, everything was immensely hot, then it cooled so that atoms and molecules could form. The common misconception is that the BB theory means everything started off in one small infinitely dense point. There are some BB theorists who like to think this and some who think we all evolved from a Black/White hole but this is not the mainstream thought.

Cheers

[Mr. Subatomic]

I don't know if this has already been said but it all relates back to Relativity. Einstein predicted that everything is moving through the space-time continuum at the speed of light, so if your travelling through the time dimension at the speed of light, you won't be moving at space. However, since a photon is moving through space at the speed of light, it has 'used up' all of its space-time speed and therefore it is unaffected by time. In a sense, the photon isn't 'aging' at all.

[Mr. Subatomic]

And yes, I also think it loses energy over time, hence the doppler shift.

Does this mean that eventually light from the most distant and earliest parts of the universe will shift into the radio spectrum? What after that?

[robagar]

Yes, and there's no upper limit on the wavelength of electromagnetic radiation, so it just becomes longer and longer wavelength radio.

Incidentally, light being red shifted into the invisible radio spectrum is part* of the solution to Olber's paradox, the paradox that in an unbounded universe any line of sight ends in the surface of a star, so the whole sky should be as bright as the sun.

* the other part is the finite age of the universe

[Paddy]

Bear with me as someone with little formal training in physics. If photons do not age or have any time effect due to their existence at light speed, how can they lose energy unless they encounter something to which impart that energy (presumably stopping in the process)? And why would they lose energy traveling in space?

Patrick

[Kal]

I touched on this on page 1. The universe is expanding - space itself is expanding. The further away an object is from us, the more it appears redshifted. Now you can attribute this redshifting to having it moving away from us - like a doppler effect to soundwaves as an ambulance drives past, but it is not that simple. It appears to be moving away from us because the space between us and it is expanding (which in effect, causes it to move away from us). Imagine a rubber band with a series of lines drawn on it, and stretch that rubber band. Lines close together are seperated by a little bit, but lines far away become seperated by large amounts. It is the same with space expanding, which is why things more distant appear more redshifted.

Because of this redshifting, the wavelength, and hence energy, is decreasing the further it travels. Consider it this way, the photon hasn't changed, just the universe around it has, & hence the way it is perceived ;)

[Paddy]

Thanks Andrew, that makes sense to me.

Patrick

[robagar]

If you want to annoy an astrophysicist, ask them why this doesn't violate the law of conservation of energy.

[avandonk]

It is very simple really. I have done the experiments. THe Sun, Moon and Wanderers go around the Earth. The evidence is irrefutable. Look for your selves.

Now the wanderers are a problem as they do not quite fit in with the perfect celestial spheres. Ok this is solved spheres within spheres never mind their intersection was inviolate. We now have a different paradigm epicycles.

The mathematics is a bit tedious but with enough epicycycles we can model anything.

What Jupiter has moons! Ok we allowed the perfect celestial spheres to intersect, what are a few more.


In the early part of last century folks other galaxies were just bits of nebulosity.

Science can only move foward by more and better testing by experiment.

As much as I admired Fred Hoyle his steady state theory is just that. An explanation that fitted with Einsteins conceptualisation of the Universe as a steady state..

I am sure I am held back by our current paradigms. We should all be like the police solving a crime, and keep an open mind.

It is a simple matter of looking at the evidence collected thus far.

I admire anyone who tries to work it out. I am still trying as well.


Bert

[avandonk]

By the way red shift is the photons getting tired and saying 'are we there yet'.

Not really!

As for annoying astrophysicists you can do much better than that!

Bert

[Mr. Subatomic]

Yeah, like saying, "Oh, so your an...astrologer?".

[Karls48]

Bert, I cannot agree with you more. As for theory of relativity (that attempts to explain the Universe and everything), there have been many very intelligent men before Einstein and all their theories bit the dust, eventually. In each of those theories formulated in the past there are grains of truth on which some one else in future builds some new concepts. To assume that we understand how the Universe developed or what the Universe is, at in this time and age of our civilisation is ridiculous.
Besides, if the space is expanding, well I have not noticed that everything is moving away from me. Ahh, that’s because we are expanding with space as well. Well, if we do why everything is moving away from us.

[xelasnave]

So where does "space" end and "matter" begin?... Does the "space"in an atom expand proportionaly, subject to the local curvatur, as space out side our galaxy?
alex

[higginsdj]

I believe the theory states that space expands where it is not otherwise under any other force (ie gravity, electrical, magnetic etc) so the forces holding the electrons in their various orbital levels is the same force, holding the electrons at their same levels regardless of whether the atom is nearby or at the other end of the universe.

Cheers

[Mr. Subatomic]

But can the expansion force overpower those other forces?

[higginsdj]

No. The expansion forces are very small - and can't even overcome gravity at the galaxy cluster level. Superclusters are not thought to be gravitationally bound - but thats a whole other story.

[ballaratdragons]

Thank you for all your many and varied (and off topic) replies.

Many of you say that light never wears out. Yet, light is always being made.

Does that mean 'Space' is getting lighter (brighter)?

If, as some of you believe, the Universe if finite, that means we will eventually be flooded by light.

Sorry, I can't go with all that.

If light was to last forever, it would have to travel on forever to 'not' brighten space. Hence an Infinite Universe, but that is another topic.

Even still, somewhere in the back of my mind is the nagging belief that light does eventually wear out (or redshift) (or alter in the radiowave spectrum).

'Dark' runs out when 'light' enters it, can 'light' run out when 'Dark' enters it? :whistle:

[Paddy]

Hi Ken,

This might be a simple-minded response to be superseded by one from a more knowledgeable contributor, but "wearing out" is not the only option for light to cease being visible light. There is red shifting as has already been pointed out, but also absorption. Photons will run into things and be absorbed. So light not wearing out or running out would not necessarily imply that the universe will continue to get brighter.

[AGarvin]

Hi Ken,



I think your delving into what is known as Olbers paradox. Have a squizz at Wiki and see if it answers some of your questions > http://en.wikipedia.org/wiki/Olbers'_paradox.

Cheers,
Andrew.

[xelasnave]

So what would happen if we found the blackest spot in a Hubble Deep field and fitted a 5 Barlow to Hubble and ran a 300 day exposure of that blackest spot:shrug:?


alex:):):)

[robagar]

You would get a very, very large bill from NASA for the telescope time

[higginsdj]

That's not a correct assumption. Yes light is absorbed BUT it is re-radiated, perhaps in another wavelength (ie Light is absorbed by Dust but immediately re-radiated in IR). This is also part of Olbers Paradox (it was interesting working this out mathematically as part of my Cosmology final exam - thanks to info on the web - but it is simple math thankfully.

Cheers

[ballaratdragons]

Good replies.

Thanks for giving me more information :thumbsup:

[Paddy]

Yes, thanks indeed for some interesting cosmological lessons!

[wasyoungonce]

Very interesting. Olbers Paradox and the sum of light intensity reaching us with regards to distribution of stars thru fractals.

Thanks to wiki.

I can finally see some use to all the advanced differentials and advanced integrations I did in specialist maths.:rofl:

Of course light must be interrupted on its journey to us and hence forth re-radiated in a different wave length.

Energy must be conserved.





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