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hornet
5,472 posts
119 months
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Gene Vincent said: Plus, for a photon there is no time at all, there is simply space and that is compressed to an instant also, its life, its journey, its entirety is compacted to an instant. This is the one thing I've always struggled with. I'm sure the equations can prove it, but I just can't get my brain round it. If a photon feels no time, yet we say it has taken 13 billion years to reach us, what exactly has the photon experienced on that journey? Indeed, is it even valid to describe it as a journey in the first place? What does the universe look like from "Johnny Photon's" point of view? Too late to be thinking about this stuff!
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boxerTen
146 posts
73 months
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hornet said: My understanding was the photons in the early universe were "trapped" in a sort of high energy "soup" and were only released once things had cooled to a certain point, allowing them to break free? Sort of similar to the how the light we see from the Sun is made of photons that have spent thousands of years migrating to its surface? Essentially that's correct. The early Universe was opaque, light didn't propagate any significant distance, instead it got scattered off the charged particles (electrons and Hydrogen and Helium nuclei) that each flew about freely and together constituted a hot plasma. It was only when the plasma of free electrons and free atomic nuclei cooled enough to condense together into neutrally charged atoms that the light ceased to be scattered - whence the Universe became transparent, circa 380,000 years post big bang.
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Bedazzled
4,088 posts
90 months
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hornet said: This is the one thing I've always struggled with. I'm sure the equations can prove it, but I just can't get my brain round it. If a photon feels no time, yet we say it has taken 13 billion years to reach us, what exactly has the photon experienced on that journey? Indeed, is it even valid to describe it as a journey in the first place? What does the universe look like from "Johnny Photon's" point of view?
Too late to be thinking about this stuff! It's a fascinating subject, because it really messes with your head! The photon is travelling at c, and according to relativity the distance to every point in its path contracts to zero; so it 'experiences' no time because it travels zero distance (t = d/s = 0/c = 0). I think one could say a photon is omnipresent.
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boxerTen
146 posts
73 months
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Blib said: AJI said: But the thing I still can't get my head around is that when they say with more and more powerful telescopes they can see further and further back in time and can see closer and closer to the big bang origin.....does this mean with a powerful enough telescope yet to be developed that they could in theory see back to the singularity itself (or read that to be the very first EM wave transmission after the big bang) ??? That's part of my issue with all of this. The Universe was an opaque plasma for its first 380,000 years so regardless of the power of one's telescope the best that is possible is to see back to this fog. In fact that is precisely what observations of the cosmic microwave background are - a view of the fog. The Universe was not opaque however to gravitational waves, so when we sort out how to observe them, it ought to be in principle possible to look back to within fractions of a second of the big bang.
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khushy
3,387 posts
88 months
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I am fascinated by all this science gibberish but do you really think that we know what happened billions of years ago - lets face it - man (we men) has trouble remembering what happened yesterday yet alone last week + the stories we concoct to get us out of trouble for not remembering what happened far out weigh the s  t that most "scientists" come up with about our origins. We are here, life is short, you will die, stars (if thats what they are) are beautiful, allwomenarenuts and petrol is running out - that's about all you can be absolutely certain of!  khushy
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mattnunn
4,114 posts
30 months
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Bedazzled
4,088 posts
90 months
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here is quite a good tool to see what is happening, if you enter omega=0.27, lamda=0.73, hubble=71 and a redshift of 8.6 for the galaxy I mentioned earlier which is 30 billion ly away...  ... you can see it was only 3.2 billion ly away from us at the moment it emitted the light we see now, but it took the light 13.1 billion years to reach us, due to inflation.
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Einion Yrth
10,402 posts
113 months
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Bedazzled said: I think one could say a photon is omnipresent. I have, half seriously, on occasion argued that THE photon is omnipresent. (all hail the Photon).
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AJI
2,018 posts
86 months
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Well I generally consider myself to be of scientific thinking, I am an engineer after all ! But for now I am just going to have to accept that I don't know enough about the fundamentals and probably some of the finer details about space-time to be able to get my head around the question arising from the OP. There have been some good replies on this thread and nicely written too, but still, I have more questions than answers and I am now going to bow out of this thread before I show myself up
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Gene Vincent
4,002 posts
27 months
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hornet said: Gene Vincent said: Plus, for a photon there is no time at all, there is simply space and that is compressed to an instant also, its life, its journey, its entirety is compacted to an instant. This is the one thing I've always struggled with. I'm sure the equations can prove it, but I just can't get my brain round it. If a photon feels no time, yet we say it has taken 13 billion years to reach us, what exactly has the photon experienced on that journey? Indeed, is it even valid to describe it as a journey in the first place? What does the universe look like from "Johnny Photon's" point of view? Too late to be thinking about this stuff! You are not alone, it is a stumbling block for many. Events along the path of a photon are simultaneous and and its path is coterminous, it doesn't seem to interact with itself. Even gravity acts on gravity! Unlike all the other elements of the Cosmos, which can effect each other and like elements, a photon appears to not do so, this does give good source material to claim there is but one photon in the entire Cosmos. This is categorically wrong and quite easily proven and shown even without the PHOJET Projects work, but you need a reasonable knowledge of probability arrows and clocks, it takes all of about 1 second for someone who understands these shortcuts to immediately grasp the reasons for the lack of interaction and it's rather prone to little gasps of delight in lectures as a toothy problem of their past disappears in an instant. That can be rewarding.
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Gene Vincent
4,002 posts
27 months
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AJI said: ...I have more questions than answers and I am now going to bow out of this thread before I show myself up If that meant disbarment from discussions I'd never be in any debate in this field, my head is filled to overflowing with questions to which there is no answer at the moment, don't feel over-horsed or inadequate, it goes with the territory, those two are my constant companions and taunt me, poking their tongues out and blowing raspberries at every turn. We are all in the dark to some extent, ask questions, it is also good for those further into the darkened room to retrace their steps back to you and ensure the trail they have been blazing in their thoughts isn't a false one. It is why anyone serious in this stuff lectures as well as just sits and thinks.
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Bedazzled
4,088 posts
90 months
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Gene Vincent said: In the 13.7 billion years since the settled period began the Cosmos has grown along with the speed limit. I'm struggling with this part as I stumble about in the dark room; distant galaxies are still moving away from us faster than light despite the physics being 'settled', i.e. the speed limit does not apply to inflation. But what is it that is inflating?
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Gene Vincent
4,002 posts
27 months
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Bedazzled said: Gene Vincent said: In the 13.7 billion years since the settled period began the Cosmos has grown along with the speed limit. I'm struggling with this part as I stumble about in the dark room; distant galaxies are still moving away from us faster than light despite the physics being 'settled', i.e. the speed limit does not apply to inflation. But what is it that is inflating? because you are looking back in time, to when it was expanding at that rate, it is confirmation of the inflation.
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Bedazzled
4,088 posts
90 months
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Gene Vincent said: Bedazzled said: Gene Vincent said: In the 13.7 billion years since the settled period began the Cosmos has grown along with the speed limit. I'm struggling with this part as I stumble about in the dark room; distant galaxies are still moving away from us faster than light despite the physics being 'settled', i.e. the speed limit does not apply to inflation. But what is it that is inflating? because you are looking back in time, to when it was expanding at that rate, it is confirmation of the inflation. I don't think that's correct, look at the calculation I posted above; that distant galaxy is currently moving away from us at 2.2x the speed of light. The rate of expansion is also increasing.
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ewenm
24,467 posts
114 months
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Bedazzled said: I don't think that's correct, look at the calculation I posted above; that distant galaxy is currently moving away from us at 2.2x the speed of light. The rate of expansion is also increasing. How do we determine what the distant galaxy is doing now given the length of time it takes information to reach us? Is it extrapolation of past behaviour?
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davepoth
19,941 posts
68 months
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My take on it:
The speed of light is a constant of a distance travelled in a period of time. The proportions of that constant remain the same from a given point of reference, however we can see examples in space (notably black holes) where distance and time get skewed. From a point of reference next to a black hole the speed of light still looks like the speed of light, but if we could see it from our point of reference it would look very different.
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Gene Vincent
4,002 posts
27 months
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Inflation occured very soon after the Big Bang, within the first second of the Universe.
The expansion of the Universe is unrelated to inflation... inflation was an extra boost on that expansion... it is likely that Inflation and the acceleration of the expansion are related, as these are very similar in nature.
The field responsible for driving Inflation the Inflaton field, but the field for driving the acceleration is Dark Energy.
It's marginally possible that these could be the same field, behaving with very different energy scales at different times in the Universe.
The more distant a galaxy is from your point of measurement, the faster it will appear to be accelerating because spacetime is highly curved at cosmological scales.
In an observational sense, it could appear to be exceeding the speed of light, meaning that one galaxy can't be observed from the other galaxy.
But that doesn't mean it's violating the speed of light in a physical sense.
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Bedazzled
4,088 posts
90 months
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ewenm said: How do we determine what the distant galaxy is doing now given the length of time it takes information to reach us? Is it extrapolation of past behaviour? It's just a calculation based on Hubble's 'constant' which in fact isn't really constant, it's decreasing over time. It also depends on the other parameters you feed into the equation, to predict how the universe will expand (red line shows the current theory):  We have to look back further in time to see faster moving galaxies which are further away, because the light has to travel further to reach us. Ironically it means slower moving galaxies with a lower red-shift can be observed further away, because we are seeing them more recently. The best analogy I can think of is jumping out of a boat on a river and trying to swim upstream. The boat (galaxy) will move downstream with the water, moving faster as it gets further away, and if the current is strong enough you (the light) will do the same thing despite your best efforts. However if the river magically widens (Hubble's constant decreases) the water at a given point will move more slowly and eventually you will start to make headway and swim up-river against the current, arriving at your destination a lot later. Otherwise you would be swept away and never seen again. (edited to add graph)
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qube_TA
6,621 posts
114 months
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Eric Mc said: So, the speed of light is increasing too.
It's not just the distances that are increasing - but the items we use to measure the distances are increasing. The measuring stick is stretching as we try to use it to measure. This!
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ewenm
24,467 posts
114 months
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qube_TA said: Eric Mc said: So, the speed of light is increasing too.
It's not just the distances that are increasing - but the items we use to measure the distances are increasing. The measuring stick is stretching as we try to use it to measure. This! But since it is a closed system and everything is expanding, does it make any sense to say distances are increasing?
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