Photon Propagation : Straightline or Helix ?

[Daecon]

Light curves downwards when it moves horizontally across a gravitational field. If it didn't, there wouldn't be any gravity.

So light curving because of gravity, causes gravity? That doesn't even make sense.

 

[paddoboy]

Do tell. Maybe you could provide evidence of these "professionals" stating that your claim : "Overall, photons emitted parallel remain parallel due to the fact that we live in a topologically flat universe as per the data from WMAP." is indeed a "fact" - and not just another "paddoboy mythical fairy tail claim of accepted mainstream theory".

I don't indulge in fairy tales my friend, and if you were certain I was wrong, you would give a link supporting that. But you can't and you won't.
It's a shame that you tend to write off anything that supports what I say as "pop science" but on thinking of your past interactions, I suppose the best one could hope for.

http://astronomy.swin.edu.au/cosmos/C/Critical+Density

http://www.opencourse.info/astronomy/introduction/35.universe_structure/

http://www.astronomy.ohio-state.edu/~thompson/1144/Lecture35.html


Perhaps you need some links re WMAP and the data from that probe?

 

[paddoboy]

http://map.gsfc.nasa.gov/universe/uni_shape.html

Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe.
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Obviously although the two parallel beams of light analogy is not mentioned, it logically follows that in a flat Universe as detailed by WMAP, that two beams emitted parallel, will remain parallel.

 

[dumbest man on earth]

I don't indulge in fairy tales my friend, and if you were certain I was wrong, you would give a link supporting that. But you can't and you won't.
It's a shame that you tend to write off anything that supports what I say as "pop science" but on thinking of your past interactions, I suppose the best one could hope for.

http://astronomy.swin.edu.au/cosmos/C/Critical Density

http://www.opencourse.info/astronomy/introduction/35.universe_structure/

http://www.astronomy.ohio-state.edu/~thompson/1144/Lecture35.html


Perhaps you need some links re WMAP and the data from that probe?

More childish "emojis" paddoboy

And, paddoboy, it is actually you that should supply evidence that directly supports your statement : "Overall, photons emitted parallel remain parallel due to the fact that we live in a topologically flat universe as per the data from WMAP."

Also, paddoboy, I did "give a link supporting that" - I was editing my Post to include it while you were so quickly Posting your usual...whatever...
So, maybe you could do a "copy/paste" of what you believe exists in any of the three links that you provided, that directly supports yopur supposed "statement" of "fact" : "Overall, photons emitted parallel remain parallel due to the fact that we live in a topologically flat universe as per the data from WMAP."

You see, paddoboy, I can and I did "give a link supporting" my certainty that what you "stated" was NOT a "fact".

 

[paddoboy]

So light curving because of gravity, causes gravity? That doesn't even make sense.

The picture Farsight is trying to convey is wrong for many reasons.
Light follows geodesics in curved spacetime.
It does also by the smallest infinitesimal amount due to its momentum, also warps spacetime some.. The same effect that we see with solar sails.

 

[paddoboy]

You see, paddoboy, I can and I did "give a link supporting" my certainty that what you "stated" was NOT a "fact".

It is a fact that the universe is topologically flat to within very small error margins according to our instruments including WMAP.
It is a fact that this means that two beams of light emitted parallel, will remain parallel.

 

[paddoboy]

Light curves downwards when it moves horizontally across a gravitational field. If it didn't, there wouldn't be any gravity.

Light travels in geodesics and follows the curvature of spacetime and the shortest possible distance between an emitter and a receiver.

 

[dumbest man on earth]

http://map.gsfc.nasa.gov/universe/uni_shape.html

Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe.
"""""""""""""""""""""""""""""""""""""""""""""""""


Obviously although the two parallel beams of light analogy is not mentioned, it logically follows that in a flat Universe as detailed by WMAP, that two beams emitted parallel, will remain parallel.

Odd, paddoboy, that you would choose to use the Link that I provided - instead of one of the three you flooded the Thread with.
Nowhere in that Link does it use the word "fact".
But, as a matter of "fact", paddoboy, it does FIRMLY STATE : "We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe."
- the ^^above quoted^^ from : http://map.gsfc.nasa.gov/universe/uni_shape.html

 

[paddoboy]

Odd, paddoboy, that you would choose to use the Link that I provided - instead of one of the three you flooded the Thread with.

It was a good link that I often use. And it reinforced exactly what I said.....
It is a fact that according to our state of the art equipment,, that the Universe is topologically flat to within very small error margins.
It is also a fact that this means that two beams of light emitted parallel, will remain parallel.
As the article also says, the universe being flat, suggests it is infinite in extent, but because it has a finite age, we only observe a finite volume.
Again, thanks for the link.

 

[dumbest man on earth]

It was a good link that I often use. And it reinforced exactly what I said.....
It is a fact that according to our state of the art equipment,, that the Universe is topologically flat to within very small error margins.
It is also a fact that this means that two beams of light emitted parallel, will remain parallel.
As the article also says, the universe being flat, suggests it is infinite in extent, but because it has a finite age, we only observe a finite volume.
Again, thanks for the link.

Still using the childish "emojis", paddoboy.

So, since "It was a good link that" you "often use", have you ever actually fully read and tried to fully understand the meaning that the Link conveys?

Evidently, I have to Post the entire content of the Link before you will admit that the Link does not support your so called "fact"?

- "Will the Universe expand forever?" ***Notice the Question Mark!!!***

"The fate of the universe is determined by a struggle between the momentum of expansion and the pull of gravity. The rate of expansion is expressed by the Hubble Constant, Ho, while the strength of gravity depends on the density and pressure of the matter in the universe. If the pressure of the matter is low, as is the case with most forms of matter of which we know, then the fate of the universe is governed by the density. If the density of the universe is less than the "critical density", which is proportional to the square of the Hubble constant, then the universe will expand forever. If the density of the universe is greater than the "critical density", then gravity will eventually win and the universe will collapse back on itself, the so called "Big Crunch". However, the results of the WMAP mission and observations of distant supernova have suggested that the expansion of the universe is actually accelerating, which implies the existence of a form of matter with a strong negative pressure, such as the cosmological constant. This strange form of matter is also sometimes referred to as "dark energy". If dark energy in fact plays a significant role in the evolution of the universe, then in all likelihood the universe will continue to expand forever."

"INFINITE UNIVERSE?" ***Again - Notice the Question Mark !!!***

"The density of the universe also determines its geometry. If the density of the universe exceeds the critical density, then the geometry of space is closed and positively curved like the surface of a sphere. This implies that initially parallel photon paths converge slowly, eventually cross, and return back to their starting point (if the universe lasts long enough). If the density of the universe is less than the critical density, then the geometry of space is open (infinite), and negatively curved like the surface of a saddle. If the density of the universe exactly equals the critical density, then the geometry of the universe is flat like a sheet of paper, and infinite in extent.

The simplest version of the inflationary theory, an extension of the Big Bang theory, predicts that the density of the universe is very close to the critical density, and that the geometry of the universe is flat, like a sheet of paper.
Measurements from WMAP

The WMAP spacecraft can measure the basic parameters of the Big Bang theory including the geometry of the universe. If the universe were flat, the brightest microwave background fluctuations (or "spots") would be about one degree across. If the universe were open, the spots would be less than one degree across. If the universe were closed, the brightest spots would be greater than one degree across.

Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe." -
- All ^^inside of quotes (" ") above" from : http://map.gsfc.nasa.gov/universe/uni_shape.html

So... "If the universe were flat, the brightest microwave background fluctuations (or "spots") would be about one degree across. If the universe were open, the spots would be less than one degree across. If the universe were closed, the brightest spots would be greater than one degree across."
Then..."the brightest spots are about 1 degree across"...and "WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error."

So : "about one degree" ... "with only a 0.4% margin of error"..
Ergo : could be 0.4% "less than about one degree across" (Open Universe)...OR...could be 0.4% "greater than about one degree across" (Closed Universe).

As is clearly stated in the Link (Again!) : "The WMAP spacecraft can measure the basic parameters of the Big Bang theory including the geometry of the universe. If the universe were flat, the brightest microwave background fluctuations (or "spots") would be about one degree across. If the universe were open, the spots would be less than one degree across. If the universe were closed, the brightest spots would be greater than one degree across."

paddoboy, the closest statement that could be construed as "Fact" - in relation to the shape of the Universe - is the final statement : "All we can truly conclude is that the Universe is much larger than the volume we can directly observe."

paddoboy, any and every person who fully reads and fully comprehends the Link : http://map.gsfc.nasa.gov/universe/uni_shape.html , knows what is "concluded" by the Author of the Link.

Please continue, paddoboy, to childishly Argue and exhibit what seem to be "Dunning-Kruger syndrome" like symptoms .
I will not participate in this Thread any longer.

 

[paddoboy]

Still using the childish "emojis", paddoboy.

Perhaps you are looking into a mirror after your past efforts...even recent ones. ...

So, since "It was a good link that" you "often use", have you ever actually fully read and tried to fully understand the meaning that the Link conveys?

Evidently, I have to Post the entire content of the Link before you will admit that the Link does not support your so called "fact"?

I know what a scientific theory is dmoe, and have spoken on it many times.
I also know that it is a fact that WMAP and the data retrieved denotes that within small error bars, the Universe is topologically flat which in turn suggests it is infinite.
I also know as a fact that taking the above, that any two beams of light emitted parallel will remain parallel.
Those to facts highlighted are all this is about, and raised by yourself in another forlorn hope that you have caught me out. Sad.
It's obvious where you are coming from as being one who has rejected/dismissed/doubts the BB in past debates.
The BB? It is of course like any scientific theory, the best model we have based on current evidence of universal/spacetime evolution. Not a fact, not certain, but damn well near certain.
Other theories of course fit also into that category the near certain nature of SR and GR for example, and of course one theory that is 100% certain is the theory of the evolution of life.
No, I do not have "Dunning-Kruger syndrome" as in essence all I am doing is supporting in the main the advances and the knowledge that mainstream cosmology interprets, based on the current evidence.
It is those that propose silly alternative scenarios, and claim they have TOE's that obviously are so affected.

 

[dumbest man on earth]

It's obvious where you are coming from as being one who has rejected/dismissed/doubts the BB in past debates.

Citation needed paddoboy.

Please provide "quoted" passages from Posts Authored by me that support your ^^above quoted^^ Ad Hominem assertion.

 

[The God]

Only if external forces sum to zero will the trajectory of a particle be on a geodesic.
That's a direct translation of the concept of Newton's $$\sum_i \vec{f}_i = m \vec{a}$$ into general relativistic terms.

Your source is talking about a universe devoid of all matter, energy and cosmological constant other that two parallel photons. No one who read your post assumed that was the case being considered. I was talking about two photons in our universe.

Here is the paper (ref 1 of your source) from 1931 which supports your claim at the end of §6 and also the end of §9:

Richard C. Tolman, Paul Ehrenfest, and Boris Podolsky. "On the gravitational field produced by light." Physical Review 37 (5) : 602. (March 1, 1931)

In order to reach that conclusion they used approximation techniques to calculate how spacetime curves about beams and pulses of light and then asked about the directional dependence of how that curvature changes the description of speed of light and geodesics of particles. For example in section §7 they show that a pencil of light has twice the gravitational attraction on stationary particles than expected from naively considering $$E=mc^2$$ to give the "mass of the photon".


I know the maths are quite rough, but here is a case where an exact solution is known.

If the at the event given by Schwarzschild coordinates $$(t,r,\theta,\phi)$$ we choose $$T^{\mu} d\lambda$$ to be the tangential light-like direction such that:
$$dt = T^{t} d \lambda = d \lambda , \; dr = T^{r} d \lambda = 0, \; d\theta = T^{\theta} d \lambda = \frac{c}{r} \sqrt{1 - \frac{r_s}{r} } d \lambda, \; dr = T^{\phi} d \lambda = 0 $$ (here I choose a dimensional $$\lambda$$ with units of time)
then it follows that if there are two nearby geodesics separated by infinitesimal bit $$X^{\mu}$$ that the geodesics diverge with an acceleration of:
$$R_{\beta \gamma \delta}^{\alpha} T^{\beta} T^{\gamma} X^{\delta} = \frac{ c^2 r_{s} \left(r - r_{s}\right)}{2 r^{4}} \begin{pmatrix} X^{t} - c^{-1} \sqrt{\frac{r^{3}}{r - r_{s}} } X^{\theta}
\\ 3 X^{r}
\\ c \sqrt{\frac{r - r_{s}}{r^{3}} } X^{t} - X^{\theta}
\\ - 3 X^{\phi} \end{pmatrix} $$
which is never zero except when $$X^{\mu} \propto T^{\mu}$$, i.e. when the "two infintesimally separated" geodesics are part of the same space-time geodesic (or when $$r_s = 0$$ which is flat space-time).

The definition of straightline in GR is as follows..

In general relativity, a geodesic generalizes the notion of a "straight line" to curved spacetime. Importantly, the world line of a particle free from all external, non-gravitational force, is a particular type of geodesic. In other words, a freely moving or falling particle always moves along a geodesic.

In that sense if there is no external force and particle moves solely due to spacetime curving, then it is straightline, however weird / curved the path be.

1.
Now there is a chink, the surface curved line of the Earth, considering the Earth as sphere, can be termed as geodesic (part of bigger circle), so its a straightline; now motion is possible on this path even with resultant external force not being zero.

2.
In general sense, in Euclidean Geometry a straightline is a path which connects two points with least distance, but in curved spacetime this path need not be the least path, still it will qualify as the Geodesic. So there is lack of clarity.

3.
Observe the orbital motion of moon around sun from infinity, it will look like helix (in traditional sense), as per definition this is a straightline, take any two points on two different orbits of the helix (after multiple pitches), I am quite confident, a photon can be made to cover these two points straight in tradiational sense, rather a particle under force also can be made to cover these two points without making the helix motion....the point is the least path can be shorter then the orbital motion of the moon. Calling the moon helix path as straightline and this particle's shorter path as non straightline is also an issue.

So that requires a rider with the definition of straightline in GR.

There are certain issues, like this definition of line in GR, which defies common sense, the concept of coordinated time in GR which makes it difficult for lay people to understand. I am sure the mainstream guys should coin different terms for these, why create removable confusions for an already non intuitive theory.

 

[The God]

...implied...
...on the contrary, origin, it was merely The God's opinion...
...drawn in...
...on the contrary, origin, you inserted yourself...

DMOE : You can refrain from responding since you are already out of this thread. Choice is yours.

But this guy Origin has the bad habit of making some wild stupid comments and then running away. I have seen that in past. The pulpable dishonesty is visible in his posts and in Paddoboy posts, as both of them will not admit mistakes, even when shown. You had to give up, but Paddoboy did not budge on his flatness, despite clear conclusion by the author.

And this habit of peek a boo (ignore...peek...ignore) is very childish, this art has been mastered by few here, one of them is Origin.

I bet he will peek, and respond on this too.....[No emojis here, as you don't like them.]

 

[The God]

Light travels in geodesics and follows the curvature of spacetime and the shortest possible distance between an emitter and a receiver.

Geodesic need not be the shortst possible distance between two points.....
Lack of basic understanding Paddoboy !

 

[dumbest man on earth]

DMOE : You can refrain from responding since you are already out of this thread. Choice is yours.

But this guy Origin has the bad habit of making some wild stupid comments and then running away. I have seen that in past. The pulpable dishonesty is visible in his posts and in Paddoboy posts, as both of them will not admit mistakes, even when shown. You had to give up, but Paddoboy did not budge on his flatness, despite clear conclusion by the author.

And this habit of peek a boo (ignore...peek...ignore) is very childish, this art has been mastered by few here, one of them is Origin.

I bet he will peek, and respond on this too.....[No emojis here, as you don't like them.]

...Noted...Noticed...and thanks for the respect...

 

[paddoboy]

Citation needed paddoboy.

Please provide "quoted" passages from Posts Authored by me that support your ^^above quoted^^ Ad Hominem assertion.

No, no citation needed. You have said in the past that either you don't accept/believe or support, or similar reference re the BB.
But if you now accept the mountain of evidence, great....welcome to the world of the scientific method.
And it certainly is not an adhom, and saying so just reflects on your own interpretations and bias.

 

[paddoboy]

Geodesic need not be the shortst possible distance between two points.....
Lack of basic understanding Paddoboy !

Reference? A geodesic is most certainly the shortest distance between two points on a curved surface.
https://www.google.com.au/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=what+is+a+geodesic+
geodesic
ˌdʒiːə(ʊ)ˈdɛsɪk,-ˈdiːsɪk/
adjective
adjective: geodesic

1. 1.
   relating to or denoting the shortest possible line between two points on a sphere or other curved surface.
   • (of a dome or other structure) constructed from struts which follow geodesic lines and typically form an open framework of triangles and polygons.

http://www.dictionary.com/browse/geodesic
geodesic
1.
Also, geodesical. pertaining to the geometry of curved surfaces, inwhich geodesic lines take the place of the straight lines of planegeometry.

http://mathworld.wolfram.com/Geodesic.html

 

[paddoboy]

DMOE : You can refrain from responding since you are already out of this thread. Choice is yours.

But this guy Origin has the bad habit of making some wild stupid comments and then running away. I have seen that in past. The pulpable dishonesty is visible in his posts and in Paddoboy posts, as both of them will not admit mistakes, even when shown. You had to give up, but Paddoboy did not budge on his flatness, despite clear conclusion by the author.

And this habit of peek a boo (ignore...peek...ignore) is very childish, this art has been mastered by few here, one of them is Origin.

I bet he will peek, and respond on this too.....[No emojis here, as you don't like them.]

You still cannot see the absolute futility of the nonsensical claims you make, and the false bravado from the limited confines of your arm chair on a science forum.
You and anyone else who is deluded enough to believe he will rewrite 21st century cosmology from such limited confines are having themselves on.
You see the world, the vast majority do not know you exist....nor I for that matter.
Any goose can claim whatever he likes on forums such as this, some though have stricter guidelines then here....I'm sure you know that from experience after similar antics on other more strict forums.
Whether you claim your magical spagehtti monster or unicorn or any mythical facsimile thereof to explain the wonders of the universe, they exist in your head only.
Science. the scientific methodology and peer review, remain the accepted standard. And I'm happy enough to say I align with that in most cases and do not find it necessary to fabricate any crazy alternative just for the sake to show some imagined invalidation of accepted cosmology. rajesh's Black Neutron Star was a prime example of such nonsense.

 

[LaurieAG]

In the following image all photons propagate in a straight line at c from their rotating sources to the observer. Were the observer to stay absolutely stationary wrt the center of mass of the rotating sources, the sources continued to emit photons during one complete rotation and there is nothing that distorts or blocks the in transit photons, all the photons shown would arrive at the observer during the next complete rotation. Were the observer to move after the observation these paths would still exist at the time of the observation.

This isn't a geodesic, the space is Euclidean and these photon paths exist between the source(s) and observer in real time at the time of the observation.

The photons propagate in a straight line although their combined paths follow a helix.