Jump to content
timharvey027

Photons don’t work

Recommended Posts

Consider this a laser beam fired between points A and B. Consider an infinite -1 observers, viewing the laser beam from all angles above below, sideways etc etc. Each observer receives photons onto their retina from the laser beam. So the light just doesn’t travel in a straight line but is seen by all observers at every angles. Does this mean that an infinite-1 number of photons travel in every direction to make the beam visible???????

Share this post


Link to post
Share on other sites

Observers not in line with the laser will not see the photons, unless the photons scatter off of something (e.g. dust). The number of photons in the beam is large but not infinite (and can be found knowing the wavelength and power)

Share this post


Link to post
Share on other sites

Hi Swansont,

What do you mean by observers not in line wiith the lasr will not see photons??   So when I see a laser beam projected into the sky in Hong Kong or at the Syndey fireworks display, I am not in line with it yet I see the laser beam....so surely I must be recieving photons on my retina from that beam ??  If I can see the laser beam, what am I seeing if not photons from it??

I really think this question is too difficult to answer as lots of people have looked at it but only you have been brave enough to offer an explanation.

Thanks and many regards

Tim

Share this post


Link to post
Share on other sites
2 minutes ago, timharvey027 said:

What do you mean by observers not in line wiith the lasr will not see photons??   So when I see a laser beam projected into the sky in Hong Kong or at the Syndey fireworks display, I am not in line with it yet I see the laser beam....so surely I must be recieving photons on my retina from that beam ??  If I can see the laser beam, what am I seeing if not photons from it??

You seem to have missed the bit that said: "unless the photons scatter off of something (e.g. dust)."

When you see a laser beam projected into the sky, you are seeing the light reflected by dust and water particles in the air.

Share this post


Link to post
Share on other sites
3 minutes ago, timharvey027 said:

Hi Swansont,

What do you mean by observers not in line wiith the lasr will not see photons??   So when I see a laser beam projected into the sky in Hong Kong or at the Syndey fireworks display, I am not in line with it yet I see the laser beam....so surely I must be recieving photons on my retina from that beam ??  If I can see the laser beam, what am I seeing if not photons from it??

I really think this question is too difficult to answer as lots of people have looked at it but only you have been brave enough to offer an explanation.

Thanks and many regards

Tim

 

On 3/10/2020 at 11:13 AM, swansont said:

Observers not in line with the laser will not see the photons, unless the photons scatter off of something (e.g. dust). The number of photons in the beam is large but not infinite (and can be found knowing the wavelength and power)

 

Share this post


Link to post
Share on other sites
8 minutes ago, timharvey027 said:

What do you mean by observers not in line wiith the lasr will not see photons??   So when I see a laser beam projected into the sky in Hong Kong or at the Syndey fireworks display, I am not in line with it yet I see the laser beam....so surely I must be recieving photons on my retina from that beam ??  If I can see the laser beam, what am I seeing if not photons from it??

In addition to the good answers above: let's assume the beam projected into the sky in Hong Kong instead would be project in space where there is almost perfect vacuum. None of the photons in the beam will scatter since there is no particles. In principle all photons will continue in a straight line. Then no observers will see any laser light, unless the observer is located exactly in a straight line from the laser. 

Share this post


Link to post
Share on other sites

Hi Swansont,

So tell me, if photons scatter of of something e.g dust, do they scatter in 360 degrees. So when everyone on say Hong Kong sees the laser beam projected into the sky, each person..lets suppose there are observers at every angle at every nanometre will all see the laser beam. If we can work out the number of photons hwich is not infinite, what happens when that number of photons is reached, or "runs out" will observers simply not see the beam

Share this post


Link to post
Share on other sites
On 3/10/2020 at 11:47 AM, timharvey027 said:

Consider this a laser beam fired between points A and B. Consider an infinite -1 observers, viewing the laser beam from all angles above below, sideways etc etc. Each observer receives photons onto their retina from the laser beam. So the light just doesn’t travel in a straight line but is seen by all observers at every angles. Does this mean that an infinite-1 number of photons travel in every direction to make the beam visible???????

Your thought experiment might be better described in terms of a light source radiating equally in all directions.

Then if there were an infinite number(1) of observers around it(2) then not all of them would receive photons because there are not an infinite number of photons to be seen.

(1) infinite-1is still infinite

(2) not practical but...

Share this post


Link to post
Share on other sites

Hi Ghideon, Thanks for your answer. I Think your missing a crucial point here. Lets suppose the laser is projected into space. An obsever on the ground must recieve photons from the beam into his retina to see it , right?   So say 200 million viewers are looking up at this laser beam, the photons, must be travelling back to their retina in order for them to see it... now that just doesn't make sense..does it??

Thanks Strange,

So what would determine who sees it and who does not?

 

Share this post


Link to post
Share on other sites
Posted (edited)
16 minutes ago, timharvey027 said:

Hi Ghideon, Thanks for your answer. I Think your missing a crucial point here. Lets suppose the laser is projected into space. An obsever on the ground must recieve photons from the beam into his retina to see it , right?   So say 200 million viewers are looking up at this laser beam, the photons, must be travelling back to their retina in order for them to see it... now that just doesn't make sense..does it??

If the laser is in the vacuum of space* and aiming into space there is no photons scatted. No observers around or behind the laser will see the beam. 

 

*) I was probably not clear on that point in my post

 

Edit: Here is an analogy.

On a really crystal clear night it is hard to see an approaching car behind a hill further down the road. 
If there is fog the scattered light will be visible before an approaching car is visible on the top of the hill:

image.png.097809385fe58a3278848aec1706ec56.png

If the car had lasers as headlights and there were vacuum it would be impossible to see the laser light until the laser shines directly into the eyes of the observer. 

Does this help?

Edited by Ghideon
added analogy, posts merged

Share this post


Link to post
Share on other sites

Hi Ghideon,

So lets assume the laser is fired between London and Paris at a hight of say half a mile above ground surface. Lets assume that there are observers at every nano centimetre at every angle along it's route including those behind the firing point and beyond the target point.  Apart from the photnos cteated from the laser itself are you telling me that observers will be viewing additional photons created by the laser photons scattering from dust particles!! Would this be consistent with the conservation of energy etc.

The point i'm trying to get accross here is that apart fromthe original laser beam of light how can an unprecendented number of observers see the beam if they are notrecieving photons from it, and if they are at any angle to it, behind it etc the number of photonsgivenof to hit observers retina must be infinite, otherwise some would not see the beam, which in practice just doesn't happen??

I do appreciate your patience in dealing with someone who has an enquiring  but not qualified mind

Share this post


Link to post
Share on other sites
26 minutes ago, timharvey027 said:

If we can work out the number of photons

The energy of a photon of red light is about 3x10-19 joules. That means for a 10W laser (typically used for a light show) there are about 3x1019 photons per second.

That is a pretty large number. About 100000000000 photons for each of your 200 million observers.

 

Share this post


Link to post
Share on other sites
1 minute ago, timharvey027 said:

Apart from the photnos cteated from the laser itself are you telling me that observers will be viewing additional photons created by the laser photons scattering from dust particles!! 

No additional photons are created. Again refer to the car light analogy i posted above. If the fog is dense enough the car will be visible only from a short distance for an observer in the fog. All photons are scattered before going very far. 

Same goes for laser. If amount of scattering is negligible a laser beam will reach moon and bounce back*. If there is dense dust or fog the laser will not be visible for anyone after some limited distance. The number of photons leaving the laser is finite. The more photons that are scattered the fewer and fewer will be left along the path of the beam.

*) https://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment

Share this post


Link to post
Share on other sites
8 minutes ago, timharvey027 said:

The point i'm trying to get accross here is that apart fromthe original laser beam of light how can an unprecendented number of observers see the beam if they are notrecieving photons from it, and if they are at any angle to it, behind it etc the number of photonsgivenof to hit observers retina must be infinite, otherwise some would not see the beam, which in practice just doesn't happen??

If they are not receiving photons, then they won't see it. There are not an infinite number of photons so an infinite number of people cannot see it. Or, to put it another way, if you are an infinite distance away you will not be able to see it. If you are just a long way away then your chance of receiving a single photon might be very small.

There are galaxies that are so distant that we only receive single occasional photons from them. Images are created over long time periods when enough photons have been received to create the image. Some galaxies are sufficiently faint and far away that we never receive any photons from them: they cant be seen.

Or a more practical example. There are reflectors on the moon left by the Apollo mission. The distance to the moon can be measured by shining a laser and detecting the returned light. The moon is so far away and the mirror is so small that it is very hard to detect the returned light. In fact, very often no returned photons are seen because there are just too few of them. This has been improved with newer telescopes:

Quote

By using a large telescope at a site with good atmospheric seeing, the APOLLO collaboration gets much stronger reflections than any existing facilities. APOLLO records approximately one returned laser photon per pulse, as opposed to the roughly 0.01 photon-per-pulse average experienced by previous LLR facilities. The stronger return signal from APOLLO translates to much more accurate measurements.

https://en.wikipedia.org/wiki/Apache_Point_Observatory_Lunar_Laser-ranging_Operation

Share this post


Link to post
Share on other sites
21 minutes ago, timharvey027 said:

Hi Ghideon,

So lets assume the laser is fired between London and Paris at a hight of say half a mile above ground surface. Lets assume that there are observers at every nano centimetre at every angle along it's route including those behind the firing point and beyond the target point.  Apart from the photnos cteated from the laser itself are you telling me that observers will be viewing additional photons created by the laser photons scattering from dust particles!! Would this be consistent with the conservation of energy etc.

The point i'm trying to get accross here is that apart fromthe original laser beam of light how can an unprecendented number of observers see the beam if they are notrecieving photons from it, and if they are at any angle to it, behind it etc the number of photonsgivenof to hit observers retina must be infinite, otherwise some would not see the beam, which in practice just doesn't happen??

I do appreciate your patience in dealing with someone who has an enquiring  but not qualified mind

If every photon was a ball bearing, the number of people that can catch one is equal to the number of ball bearings fired; two people cannot catch one. Two people cannot see the same photon.

Share this post


Link to post
Share on other sites
Posted (edited)

Again Thank you Strange and Gideon,

for your informative answers, the clouds are slowly clearing. It would be great if I could have a brief chat in person. I think by takinng examples or thought experiments to extremes you can often determine why something is still not quite right with our understanding of light and gravity. Hope we can chat.

Regards

Tim

Hi Stringjunky,

I get that, so what happens when the finite amount of photons produced runs out to the infinite nuber of observers?

regards

Tim

 

Edited by timharvey027

Share this post


Link to post
Share on other sites
3 minutes ago, timharvey027 said:

It would be great if I could have a brief chat

I thought that is what were doing. :)

 

Share this post


Link to post
Share on other sites
Posted (edited)
48 minutes ago, timharvey027 said:

Again Thank you Strange and Gideon,

for your informative answers, the clouds are slowly clearing. It would be great if I could have a brief chat but not sure that is allowed on this forum. I think by takinng examples or thought experiments to extremes you can often determine why something is still not quite right with our understanding of light and gravity. Hope we can chat.

Regards

Tim

Not a good idea Tim to put your details up. I advise you to edit your post and delete them.

Edited by Strange
Edit out personal details

Share this post


Link to post
Share on other sites
4 minutes ago, timharvey027 said:

I get that, so what happens when the finite amount of photons produced runs out to the infinite nuber of observers?

Then the remaining ones don't see anything.

There are plenty of things we can't see because not enough photons reach our eyes. 

Share this post


Link to post
Share on other sites
1 minute ago, timharvey027 said:

Thanks Sting Junky for your advise re personal details, edited.

Regards

Tim

No prob. :)

Share this post


Link to post
Share on other sites
42 minutes ago, timharvey027 said:

The point i'm trying to get accross here is that apart fromthe original laser beam of light how can an unprecendented number of observers see the beam if they are notrecieving photons from it, and if they are at any angle to it, behind it etc the number of photonsgivenof to hit observers retina must be infinite, otherwise some would not see the beam, which in practice just doesn't happen??

It does happen.

You seem to be assuming that light can be infinitely divided. It cant be. 

Share this post


Link to post
Share on other sites
Posted (edited)

Hi Strange,

That is my point, if light can't be infinitely divided how come an infinite number of people could see the laser beam firing between london and paris (thought wise, assuming you could get an infinite people in that space to view it) , they all must be recieving photons to the retina to view it. If there are ony a finite number of photons produced by the laser how could this work. And if the anwser is that only those that recieved photons would be able to see the beam, what determines who would recieve those photons in preference to another??

Help me here, is this thought provoking or am I just being thick?

Edited by timharvey027

Share this post


Link to post
Share on other sites
Posted (edited)
19 minutes ago, timharvey027 said:

Hi Strange,

That is my point, if light can't be infinitely divided how come an infinite number of people could see the laser beam firing between london and paris (thought wise, assuming you could get an infinite people in that space to view it) , they all must be recieving photons to the retina to view it. If there are ony a finite number of photons produced by the laser how could this work. And if the anwser is that only those that recieved photons would be able to see the beam, what determines who would recieve those photons in preference to another??

Help me here, is this thought provoking or am I just being thick?

An infinite number of people can't see a finite number of photons. A photon can only interact with one eye. If a 100 photons are emitted only a 100 possible people could see them.

Edited by StringJunky

Share this post


Link to post
Share on other sites
22 minutes ago, timharvey027 said:

That is my point, if light can't be infinitely divided how come an infinite number of people could see the laser beam firing between london and paris (thought wise, assuming you could get an infinite people in that space to view it)

They couldn't.

22 minutes ago, timharvey027 said:

nd if the anwser is that only those that recieved photons would be able to see the beam, what determines who would recieve those photons in preference to another??

Just chance. Imagine throwing a large (but not infinite) number of grains of rice into a large crowd (like a football stadium full, for example). Some people would get a handful of rice, some would get 1 or 2 grains and some would get none.

The problem seems to be that you are thinking of light as something continuous, more like water, say. If you filled the stadium with water, then everyone would get wet!

25 minutes ago, timharvey027 said:

Help me here, is this thought provoking or am I just being thick?

i don't think you are being thick. A lot of people struggle with this, I think. The problem is one of scale and our intuitions. We are used to thinking of light as continuous and infinitely divisible, because that is how it seems to behave in everyday situations. And there are such a large number of photons in most light sources that it is pretty close to being continuous. That is why using the photon model isn't very helpful in a lot of cases.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.