Special Relativity - Could we see it ?

[andrew s]

1 hour ago, SilverAstro said:

We dont all have the time to read up on these things to the extent of questioning Gamow et al, so we do need popularisers of science.

I agree. It was hot and I had just mover 900kg of gravel by hand up a steep hill so I was feeling ... ...well I have had a beer now and am calm and accepting.

If you do want to get an insight into what a photon is have a look at this  http://www.osa-opn.org/Content/ViewFile.aspx?Id=3185. I am still working through it.

Regards Andrew

[SilverAstro]

27 minutes ago, andrew s said:

I had just mover 900kg of gravel by hand up a steep hill so I was feeling

Ah! that's ok Sisyphus, I'm sure the collective understands   but next time please avail yourself of my new improved telekinesis machine, much better than competing StarTrek devices.

Thanks for the link, looks good and should keep me out of mischief for a wee while

[Macavity]

1 hour ago, andrew s said:

I never said real photon don't exist I agree they are created and detected. Can you provide a
reference to accurate reconstruction to their path through space?

Perhaps. But it's over twenty years since I was actively designing detectors for
Particle Physics experiments at CERN / DESY.  If you are happy enough that 
photon detectors (e.g. in the form of lead glass arrays or "calorimeters") exist,
you can perhaps understand that the method of reconstructing events from
e.g. particle physics collisions is rather complex... but also possible.

Accurate reconstruction of paths of *particles* emmanating from collisions is 
rather limited to those that are charged... via Drift chambers, CCD arrays etc.
But *energy* of photons can be measured both quantitatively and to some
extent spatially. Even neutrinos can be "detected" ... or rather their presence
inferred by *missing* energy etc. But we digress beyond this discussion. 

But we are talking SEMANTICS (I looked it up!) not "method of detection"?
Not quite sure how  "QED" and "Feynman Diagrams" come in to this, but!
Sorry to be picky, re. spelling of Hawking etc., but it's an easy rejoinder. lol.
You do use quite *evocative*  even quite accusatory terms re. "scientists".

In my younger days, I would loved to have "entrapped and seduced the lay
person with seductive images and analogies", but good looks count more?

[SilverAstro]

15 minutes ago, Macavity said:

Sorry to be picky, re. spelling of Hawking etc., but it's an easy rejoinder. lol.

Arrrr Jim lad, it be a'thart talk of intelligent parrots by Stub wot did give 'im the Black Spot. X

 

[SilverAstro]

 

Anyway back to business :-

 

On 17/07/2016 at 18:22, Tiki said:

As an object passes through the 'speed of light barrier' It cant

you'd certainly expect an 'optical boom'. Nope. Only if you were to reinvent the aether, otherwise there is nothing to 'push' through. Just because they both share a word, "barrier", doesnt mean they should share our 'expectations'

Some neutrino detectors look for an 'optical shockwave' of Cherenkov radiation which shows the acceleration , deceleration ,  of a particle faster than the speed ,phase velocity,  of light (in that medium). Isnt it strange that "medium" always ends up in parenthesis ! Cherenkov is not doing anything contrary to the so called speed of light barrier, it is not exceeding c.

 

[andrew s]

1 hour ago, Macavity said:

Accurate reconstruction of paths of *particles* emmanating from collisions is 
rather limited to those that are charged... via Drift chambers, CCD arrays etc.
But *energy* of photons can be measured both quantitatively and to some
extent spatially. Even neutrinos can be "detected" ... or rather their presence
inferred by *missing* energy etc. But we digress beyond this discussion. 

You clearly have a good understanding of Physics (quite probably much better than mine) and I was not trying to challenge that.  

I have not been active in Physics for over 35 years but had always wondered how the world we see emerges from the underlying quantum reality and so had tried to keep up via mainly popular expositions. Quite by chance I came across decoherence theory. In my attempts to understand it I was led to restudy quantum mechanics and got a big shock to realise that most (possibly all) of what I had learned about quantum mechanics in the 1970's as an undergraduate and graduate student of Physics was just wrong and was now considered the old quantum mechanics.

Photons in particular seem to be at an extreme of this being spin 1 particles and thus obeying Bose Einstein statistics. This leads to many complications in that in QED they have well define Energy, Momentum and Polarisation and thus are completely undefined in position and time. To make matters worse when there is more than one, and it is difficult but not impossible to create single photon states, they have to be treated as an aggregate whole and ideas of single photon trajectories make no sense. Only at the points of creation and annihilation are single photon considered. This is not the case for non-integer spin "particles" where I am quite happy to accept that one can (and you did) reconstruct their trajectories.

 Regards Andrew

PS If I offended anyone that was not my intention and I apologise.

[SilverAstro]

2 hours ago, andrew s said:

This leads to many complications in that in QED they have well define Energy, Momentum and Polarisation and thus are completely undefined in position and time.

PS If I offended anyone that was not my intention and I apologise.

No problems here Andrew, your contributions have been most interesting. In fact I have enjoyed everyone's bits   and likewise if I have sounded at all heavy handed  please all accept my apols (typing is very longwinded and without clues from body language)

Now then, this Bose-Einstein stuff, yep heard of their condensates and things ! just how undefined in position ,  universe wide ?  is this Son of Heisenberg stuff,   hmmm scratches head and continues googling but it is getting late , , ,

All very entertaining for cloudy nights

 

[Macavity]

8 hours ago, SilverAstro said:

No problems here Andrew, your contributions have been most interesting. In fact I have enjoyed everyone's bits   and likewise if I have sounded at all heavy handed  please all accept my apols (typing is very longwinded and without clues from body language)

I entirely echo the above - which was well put. For my own part, I do "mess about"
(some people may not like this!) but it is never my intent to belittle or to hurt...

To be honest, I like a bit of "banter"... Or even "cheerful irreverence" with a fellow
kindred spirit here! I sometimes enjoy trading on respective real life backgrounds. 
For me, SGL is a fun, but purely *recreational*, activity? Creation of a "respected
internet persona" will doubtless ever elude me? lol.  And is not ME anyway...

[Physicist13]

hmmm trying to stay out of this ;)...but just to say. So far special Rel, Gen rel and QM have passed all the tests thrown at them to within the best achievable experimental limits. Experimentalists constantly try to do more precise measurements to keep testing these theories and possibly show a brakedown. In general, theorists modify or more rarely come up with new or refined theories that also have to pass all current tests but may also predict some new features which are measurable. Hypothetical arguments can be stimulating and thought provoking but must lead to some prediction of a verifiable experimental test.

[Stub Mandrel]

2 hours ago, Physicist13 said:

Hypothetical arguments can be stimulating and thought provoking but must lead to some prediction of a verifiable experimental test.

You can't know if they will lead to anything useful at the start. That's the definition of speculation - trying something with no guarantee of success or reward.

[andrew s]

7 minutes ago, Stub Mandrel said:

You can't know if they will lead to anything useful at the start. That's the definition of speculation - trying something with no guarantee of success or reward.

Quite right but there are two extreme forms of speculation (and everything in between) in Physics.

Firstly, parlor game or easy speculation where you throw out ideas and ask what if etc. No serious attempt is made to drive to a rigorous conclusion. This type is fun and I hope undertaken mainly for pleasure.

Secondly, the science (Physics) game or hard speculation where the ideas are given mathematical form linked to current experimental results & knowledge and predictions made (and tested if possible). This type leads to progress in science and if very good Nobel prizes. A good example would be Einstein's speculation on what it would be like to ride a light beam which led him to SR.

I quite like both in context.

I put "and tested if possible" in brackets as there is a trend to argue that testing is not necessary in certain areas of Physics, I strongly disagree with this, and in my view that would be Meta Physics or mathematical sophistry. (No offence intended.)

Regards Andrew

[Tiki]

 

16 hours ago, SilverAstro said:

As an object passes through the 'speed of light barrier' It cant

you'd certainly expect an 'optical boom'. Nope. Only if you were to reinvent the aether, otherwise there is nothing to 'push' through. Just because they both share a word, "barrier", doesnt mean they should share our 'expectations'

Some neutrino detectors look for an 'optical shockwave' of Cherenkov radiation which shows the acceleration , deceleration ,  of a particle faster than the speed ,phase velocity,  of light (in that medium). Isnt it strange that "medium" always ends up in parenthesis ! Cherenkov is not doing anything contrary to the so called speed of light barrier, it is not exceeding c.

 

 

It cant . It does in the hypothetical situation that is under consideration.

Only if you were to reinvent the aether, otherwise there is nothing to 'push' through. Since we have dispensed with SR then why not further extend the thought experiment by reinventing 'nothing' and 'aether'.

 

 Isnt it strange that "medium" always ends up in parenthesis !

 

Not always.

https://en.wikipedia.org/wiki/Neutrino_detector#Cherenkov_detectors

From the Wikipedia 'neutrino-detector' article :"Ring-imaging" Cherenkov detectors take advantage of a phenomenon called Cherenkov light. Cherenkov radiation is produced whenever charged particles such as electrons or muons are moving through a given detector medium somewhat faster than the speed of light in that medium. In a Cherenkov detector, a large volume of clear material such as water or ice is surrounded by light-sensitive photomultiplier tubes. A charged lepton produced with sufficient energy and moving through such a detector does travel somewhat faster than the speed of light in the detector medium (although somewhat slower than the speed of light in a vacuum). The charged lepton generates a visible "optical shockwave" of Cherenkov radiation. This radiation is detected by the photomultiplier tubes and shows up as a characteristic ring-like pattern of activity in the array of photomultiplier tubes. As neutrinos can interact with atomic nuclei to produce charged leptons which emit Cherenkov radiation, this pattern can be used to infer direction, energy, and (sometimes) flavor information about incident neutrinos.

Cherenkov won the 1958 Nobel Prize for Physics for his work on the radiation that now bears his name.

 

Cherenkov is not doing anything contrary to the so called speed of light barrier, it is not exceeding c. I almost totally agree. Nothing has ever been known to exceed the speed of light in a vacuum. The speed of light in water (approx. 2/3 the speed of light in a vacuum) is sometimes exceeded by certain particles (in the water) that absorb sufficiently energetic neutrinos.

 

IMO, Cherenkov radiation is very counter-intuitive but really quite amazing.

[Stub Mandrel]

I think idle speculation can lead to valid results. In chemistry the ring-structure of benzene is an example.

[andrew s]

43 minutes ago, Stub Mandrel said:

I think idle speculation can lead to valid results. In chemistry the ring-structure of benzene is an example.

I take the point, but I am not too sure how idle Kekule speculation was. He was actively looking for the structure of benzene so he was well primed to have his dream of a snake catching it's tail. He then went and worked out the structure. So to me it is an example of my hard speculation. I have no doubt that letting ones mind wonder aimlessly about a problem works (I do it myself) but the key difference is doing the work after the insight.

Regards Andrew

[Tiki]

1 hour ago, Stub Mandrel said:

I think idle speculation can lead to valid results.

The whole of science abounds in such results. Quantum mechanics is perhaps the quintessential such result. Einstein famously speculated about what it would be like to fall off a roof and came up with GR; he also wondered what it would like ride along next to a ray of light and came up with SR.......

[Physicist13]

Sorry but QM def not a result of idle speculation!!!! 

[SilverAstro]

2 hours ago, Physicist13 said:

Sorry but QM def not a result of idle speculation!!!! 

(Albert) But that does not mean we have to like it (/E),   but seriously, yes, I agree

 

On 19/07/2016 at 08:45, Physicist13 said:

hmmm trying to stay out of this ;)..

Not going too well is it (waves very big joke flag )  [Where's macavity when I need him, he is supposed to be chief in charge of the jest round here ?? ]    but seriously, keep it up, very interesting.

[SilverAstro]

23 hours ago, Tiki said:

It cant . It does in the hypothetical situation that is under consideration.

Not always.

From the Wikipedia 'neutrino-detector' article

Cherenkov is not doing anything contrary to the so called speed of light barrier, it is not exceeding c. I almost totally agree.

 

IMO, Cherenkov radiation is very counter-intuitive but really quite amazing.

There is always a need to keep an open mind during hypotheticals but

and thank you for the massive quote from Wiki, I thought it obvious previously that we knew all about Cherenkov ( I did stay awake through some of the Physics lectures y'know)

I agree ! it really is amazing and also quite amazing that I agree with you !! howzat ?

 

[Macavity]

7 minutes ago, SilverAstro said:

Where's macavity when I need him, he is supposed to be chief in charge of the jest round here ??

Heheh. I'm probably just "sealing my fate" on another thread? lol.  But only
to object that normal *personalised* conflict is becoming too impersonal!
 

[andrew s]

On 7/19/2016 at 23:38, SilverAstro said:

Now then, this Bose-Einstein stuff, yep heard of their condensates and things ! just how undefined in position ,  universe wide ?  is this Son of Heisenberg stuff,   hmmm scratches head and continues googling but it is getting late , , ,

All very entertaining for cloudy nights

 

Just noticed this comment. The problem is that for massless spin 1 particles there is no position operator and hence no corresponding observable! All QED will do is give you detection probabilities of photons at specific locations. So asking about their position is, according to QED, meaningless although I suspect a good topic for speculation, idle or otherwise. 

 

Regards Andrew

[Macavity]

3 hours ago, SilverAstro said:

Thank you for the massive quote from Wiki, I thought it obvious previously that we knew all about Cherenkov
( I did stay awake through some of the Physics lectures y'know)

https://youtu.be/dJmg-879j5o
In suitably masculine tones.

 

[SilverAstro]

1 hour ago, Macavity said:

https://youtu.be/dJmg-879j5o
In suitably masculine tones.

That's 'im, the one I was thinking of when I posted here :- https://stargazerslounge.com/topic/273577-unattended-baggage/?do=findComment&comment=2998476

Well done