Do we observe the orignial photon?

[acey]

Like I said above, this is much easier to understand if you stop thinking of a photon as an object & start thinking of it as a probability function, the object (wave, particle or some combination of the two) not actually existing until it is detected.

This business of "not actually existing until it is detected" is of course the tricky point. When I was doing my PhD in theoretical physics I used to ask people how it is that a virtual photon can know it's virtual, and I've never really heard a satisfactory answer.

As to its being a probability function, obviously it isn't, though Born's rule tells us how to relate wave functions to probabilities.

As you note, there is clearly a distinction between seeing-as-detecting and seeing-as-experiencing; either sense is problematic.

[brianb]

As to its being a probability function, obviously it isn't

It's everywhere. The probability function tells you just how probable it is that it will be detected at any given place.

[Earl]

Nope. Uranium 238 (depleted of the small fraction of U235 which occurs in natural uranium) decays to Thorium 234 by alpha decay with a half life of 4.468 billion years.

Depleted uranium is actually used for radiation shielding in medical radiotherapy equipment, where it will be contaminated by the strong gamma ray sources used (e.g. cobalt 60) and become secondarily radioactive as a consequence. It is also used extensiveley for making couterweights for control surfaces in aircraft, and for ballistic munitions (bullets), where its high density is a valuable property. The radioactivity of depleted uranium is not a significant hazard but its chemical toxicity is.

These Depleted munitions are in the process of been banned if i recall or research into getting them banned, due to damage to the enviroment. (nothing compaired to the damage to the target !)

Probably plenty of these rounds in the desert thanks to lots of A-10's in action for the last 10 years.

[starf]

Those science videos were worth watching. did he actually say

"The mirror has got nothing to do with the price of cheese"?

[great_bear]

I've ordered Feynman's book The Strange Theory of Light and Matter as a result of this thread.

[661-pete]

Whether the photon that strikes our objective or primary, is the 'same' photon as the one that left that distant object all those years ago ... well I've sometimes wondered about that. I mean, assume that 100 million years ago and 600 million million million miles away, just one little atom in one insignificant star in that remote galaxy, happened to undergo a transition and emit a particular photon. And that photon somehow survived a journey lasting 100 million years and ended up striking my primary, which was its final act ... it sounds like an amazing epic journey! Please don't disillusion me! OK, so if it's only a causal relationship, the photon itself didn't really exist throughout its journey from A to B. The causal connection existed along that path, all those zillions of miles. For if the galaxy hadn't been there, that photon wouldn't have hit my telescope...

[Layor]

Well.... I've just read all the way through this and all I keep thinking about is a quote from the 'Goons' about..bringing an logical argument to its illogical conclusion:D:D:D

But it was a bl***y good read:icon_salut:

Layor.

[ollypenrice]

For an even better read, grab yourself a copy of Feynman's QED. He's the man.

Olly