> This is a *stupidly tiny number*. If you asked POV-Ray to render this, and 
> you sent out a million, billion, trillion rays, every single damned one 
> would completely miss such a tiny object. It seems astonishing to me that 
> such an absurdly minute object is visible at all - but Wikipedia claims it 
> is...

Good job the real world isn't a backward raytracer then :-)

I suspect even a true point source (ie no physical size) was sending out the 
same amount of light from that distance, you would be able to see that too.

Post a reply to this message

>> This is a *stupidly tiny number*. If you asked POV-Ray to render this, 
>> and you sent out a million, billion, trillion rays, every single 
>> damned one would completely miss such a tiny object. It seems 
>> astonishing to me that such an absurdly minute object is visible at 
>> all - but Wikipedia claims it is...
> 
> Good job the real world isn't a backward raytracer then :-)

Yeah. Because then we wouldn't be able to see stars... which... would be 
bad... somehow. I'm sure. :-)

I guess it's simply the case that all the light gets focused onto a 
point smaller than a single light sensor, which never the less registers 
that there's some light there. (Also, presumably no lense can ever be 
optically perfect...)

The part that really puzzles me as that even on the clearest, most 
cloudless night, there are, like, maybe 3 stars visible in the entire 
sky. And yet mankind has names for hundreds and hundreds of stars, many 
of which are claimed to be "visible to the naked eye".

I can only presume this must be due to light pollution. (I'm not saying 
that MK's street lighting is inefficient, but... you *can* tell where 
the city is from about 15 miles away just by the fact that one entire 
side of the night sky is glowing at the exact wavelength of the Sodium 
D-line...) Still, even on school caving trips in the middle of nowhere, 
I don't recall seeing many stars in the night sky. I presume they're 
still there, we just can't see them any more.

> I suspect even a true point source (ie no physical size) was sending out 
> the same amount of light from that distance, you would be able to see 
> that too.

Well, photons are quantum, right?

(Interestingly, I'm told it *is* possible to make a light source that 
emits individual photons, one at a time, on que. And that when you do 
this, things like the double-slit experiment still show multiple waves 
interferring and reinforcing - despite this being obviously 
impossible... Wave-particle duality is weird!)

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> OK, so according to the best data I could get my hands on, Alpha Centuri
> A is about 430 light years away

Um, I'm pretty sure that should be 4.3 lightyears.

http://en.wikipedia.org/wiki/Alpha_centauri

That will make your numbers a little more sensible. There are very few naked-eye
stars that are as far as 400 lightyears - only highly luminous giants like
betelgeuse.

:)

Post a reply to this message

>> OK, so according to the best data I could get my hands on, Alpha Centuri
>> A is about 430 light years away
> 
> Um, I'm pretty sure that should be 4.3 lightyears.
> 
> That will make your numbers a little more sensible. There are very few naked-eye
> stars that are as far as 400 lightyears - only highly luminous giants like
> betelgeuse.
> 
> :)

EPIC FAIL. >_<

Maybe I should just go away and live in a box somewhere. :-S

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> The part that really puzzles me as that even on the clearest, most
> cloudless night, there are, like, maybe 3 stars visible in the entire
> sky. And yet mankind has names for hundreds and hundreds of stars, many
> of which are claimed to be "visible to the naked eye".
>
> I can only presume this must be due to light pollution.

Entirely. There are over a thousand stars visible to the naked eye.

http://en.wikipedia.org/wiki/Naked-eye_stars#Naked_eye_in_astronomy

There is nothing like spending a couple of hours on your back in a field with a
truly dark sky - it feels like there are far more than mere thousands visible!

:o

Post a reply to this message

Bill Pragnell wrote:
> Invisible <voi### [at] devnull> wrote:
>> The part that really puzzles me as that even on the clearest, most
>> cloudless night, there are, like, maybe 3 stars visible in the entire
>> sky. And yet mankind has names for hundreds and hundreds of stars, many
>> of which are claimed to be "visible to the naked eye".
>>
>> I can only presume this must be due to light pollution.
> 
> Entirely. There are over a thousand stars visible to the naked eye.
> 
> http://en.wikipedia.org/wiki/Naked-eye_stars#Naked_eye_in_astronomy
> 
> There is nothing like spending a couple of hours on your back in a field with a
> truly dark sky - it feels like there are far more than mere thousands visible!
> 
> :o

But where do you have to go? Outer Mongolia?

(Also... where the hell *is* that anyway?!)

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> But where do you have to go? Outer Mongolia?

Well, I bet the skies are great there(!), but at least 50 miles from a large
town or city would do in the UK. Simply making sure you can't see an artificial
light source directly by eye will make a big difference. Coastline works well
because you've only got to worry about distance from towns in half as many
directions. Wilderness such as moorland or mountains works best of course
(although steep hills will obstruct part of the sky), but I'm sure you could
find somewhere suitable within a short drive of MK. Also, winter is best because
the cold air holds less moisture and is therefore clearer. Try to make sure the
moon isn't up either, it can produce a surprising quantity of light pollution,
especially when full!

Oh, and pick a cloudless night ;-)

Post a reply to this message

> Still, even on school caving trips in the middle of nowhere, I don't 
> recall seeing many stars in the night sky. I presume they're still there, 
> we just can't see them any more.

http://www.astro-travels.com/pictures/Europe-Light-Pollution.jpg

On the above map my house is on the border of a green/yellow region and I 
can make out a huge number of stars on a clear night, the Milky Way is also 
just barely visible on a really good night.  I don't know exactly where MK 
is on that map, but it looks a bit red/orange around there :-(

Don't forget you need to go outside for at least 20 minutes or so for your 
eyes to get fully adjusted to the dark, initially it might look like only a 
dozen or so stars are visible, but after a few minutes you will see hundreds 
more.

BTW if you're interested, one of the brightest "stars" in the sky at the 
moment is actually Jupiter.

Post a reply to this message

>> Still, even on school caving trips in the middle of nowhere, I don't 
>> recall seeing many stars in the night sky. I presume they're still 
>> there, we just can't see them any more.
> 
> http://www.astro-travels.com/pictures/Europe-Light-Pollution.jpg
> 
> On the above map my house is on the border of a green/yellow region and 
> I can make out a huge number of stars on a clear night, the Milky Way is 
> also just barely visible on a really good night.

Aren't we *in* the Milky Way?

> I don't know exactly 
> where MK is on that map, but it looks a bit red/orange around there :-(

I would suggest that MK is the small red dot just NW of London. (Or if 
it isn't, it's in that general direction.)

> Don't forget you need to go outside for at least 20 minutes or so for 
> your eyes to get fully adjusted to the dark, initially it might look 
> like only a dozen or so stars are visible, but after a few minutes you 
> will see hundreds more.

We drove to and from work through lots of wilderness, and at this time 
of night it's quite dark even at 5PM. Many of the roads aren't lit.

I don't recall where we get dragged to on our school caving trips, but 
we seemingly had to drive for many hours along winding rounds lined with 
dry stone walls before reaching the nearest building with electricity.

> BTW if you're interested, one of the brightest "stars" in the sky at the 
> moment is actually Jupiter.

Any ideas what the visual angle for that is? ;-)

Post a reply to this message

> Aren't we *in* the Milky Way?

Yes, and it's quite a flat disc, so looking out from Earth along the plane 
of the disc you see a lot more stars than looking out perpendicular to it, 
this looks like a brighter band going across the sky.

>> BTW if you're interested, one of the brightest "stars" in the sky at the 
>> moment is actually Jupiter.
>
> Any ideas what the visual angle for that is? ;-)

Wikipedia tells me the radius is 71500 km, Stellarium tells me it's 5.224 AU 
away from us, so googling "2*71500 km / 5.224 AU in degrees" gives 0.01 
degrees.

Post a reply to this message

>> Aren't we *in* the Milky Way?
> 
> Yes, and it's quite a flat disc, so looking out from Earth along the 
> plane of the disc you see a lot more stars than looking out 
> perpendicular to it, this looks like a brighter band going across the sky.

I will admit I don't know much about the geometry of our galaxy, but I 
was under the impression that the disk is hundreds of billions of light 
years "thick", it's just that it's quadrillions of light years across as 
well. The point being, the disk is many million stars thick, and so we 
should see them in just about every direction we look.

>>> BTW if you're interested, one of the brightest "stars" in the sky at 
>>> the moment is actually Jupiter.
>>
>> Any ideas what the visual angle for that is? ;-)
> 
> Wikipedia tells me the radius is 71500 km, Stellarium tells me it's 
> 5.224 AU away from us, so googling "2*71500 km / 5.224 AU in degrees" 
> gives 0.01 degrees.

So... about 36 seconds of arc. Man, that's pretty small.

Post a reply to this message

"scott" <sco### [at] scottcom> wrote:
> > Aren't we *in* the Milky Way?
>
> Yes, and it's quite a flat disc, so looking out from Earth along the plane
> of the disc you see a lot more stars than looking out perpendicular to it,
> this looks like a brighter band going across the sky.

This is a pretty awesome photo of the whole thing:

http://en.wikipedia.org/wiki/File:Deathvalleysky_nps_big.jpg

Not exactly what you'd see with the naked eye but it gives you the idea.

> >> BTW if you're interested, one of the brightest "stars" in the sky at the
> >> moment is actually Jupiter.
> >
> > Any ideas what the visual angle for that is? ;-)
>
> Wikipedia tells me the radius is 71500 km, Stellarium tells me it's 5.224 AU
> away from us, so googling "2*71500 km / 5.224 AU in degrees" gives 0.01
> degrees.

Jupiter and Saturn are particularly easy to pick out, because they're big enough
to be actual discs rather than points like regular stars. And if you can hold
binoculars steady enough you'll just about see Saturn's rings.

Post a reply to this message

Bill Pragnell wrote:

> This is a pretty awesome photo of the whole thing:
> 
> http://en.wikipedia.org/wiki/File:Deathvalleysky_nps_big.jpg
> 
> Not exactly what you'd see with the naked eye but it gives you the idea.

This is awesomer:

http://en.wikipedia.org/wiki/File:Perseid_Meteor.jpg

Here in the name of God does the night sky actually look like this?!

Post a reply to this message

> I will admit I don't know much about the geometry of our galaxy, but I was 
> under the impression that the disk is hundreds of billions of light years 
> "thick",

It's much smaller than you think:

http://en.wikipedia.org/wiki/Milky_way

> So... about 36 seconds of arc. Man, that's pretty small.

It's still one of the very few objects in the sky that allows you to 
actually see its shape with a good pair of binoculars or a small telescope 
though.

Post a reply to this message

>> I will admit I don't know much about the geometry of our galaxy, but I 
>> was under the impression that the disk is hundreds of billions of 
>> light years "thick",
> 
> It's much smaller than you think:
> 
> http://en.wikipedia.org/wiki/Milky_way

Heh, "only" 100,000 light years across and 1,000 light years thick. 
Well, that's the trouble when you start dealing with Really Huge 
Numbers, see?

There's a reason why would talk about 4 Terabytes rather than 
4,000,000,000,000 bytes - it's frighteningly easy to get the number of 
digits wrong! ;-)

Obligatory XKCD:

http://xkcd.com/558/

Post a reply to this message

> This is a pretty awesome photo of the whole thing:
>
> http://en.wikipedia.org/wiki/File:Deathvalleysky_nps_big.jpg
>
> Not exactly what you'd see with the naked eye but it gives you the idea.

I always wonder how they get these type of photos.

I mean this must be a pretty long exposure to get that detail?  But since 
the Earth is rotating, either the ground or the sky is going to get motion 
blurred.  Is this a photoshop of two images, or can they really get a photo 
like that in one shot?

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> This is awesomer:
>
> http://en.wikipedia.org/wiki/File:Perseid_Meteor.jpg
>
> Here in the name of God does the night sky actually look like this?!

Well, that's an even longer exposure than the one I posted (you can tell by the
way the stars are slightly elongated), so no, that's not exactly what you'd see
by eye either. But similar!

A shame there's only one meteor visible there, I was expecting more...

Post a reply to this message

"scott" <sco### [at] scottcom> wrote:
> > I will admit I don't know much about the geometry of our galaxy, but I was
> > under the impression that the disk is hundreds of billions of light years
> > "thick",
>
> It's much smaller than you think:
>
> http://en.wikipedia.org/wiki/Milky_way

I always remember galactic vital statistics by knowing all the lyrics to this:

http://en.wikipedia.org/wiki/Galaxy_song

:-)

Post a reply to this message

> I always remember galactic vital statistics by knowing all the lyrics to this:
> 
> http://en.wikipedia.org/wiki/Galaxy_song
> 
> :-)

Is that something like the song about the table of elements?

Post a reply to this message

"scott" <sco### [at] scottcom> wrote:
> > This is a pretty awesome photo of the whole thing:
> >
> > http://en.wikipedia.org/wiki/File:Deathvalleysky_nps_big.jpg
> >
> > Not exactly what you'd see with the naked eye but it gives you the idea.
>
> I always wonder how they get these type of photos.
>
> I mean this must be a pretty long exposure to get that detail?  But since
> the Earth is rotating, either the ground or the sky is going to get motion
> blurred.  Is this a photoshop of two images, or can they really get a photo
> like that in one shot?

I'm not sure. The fact that it's a nearly-complete panorama makes it even more
complicated - I guess it must have been unwrapped from a fisheye.

I'd think it was a single shot. I bet you could get away with up to a minute of
exposure, and it's very wide angle so any movement would be less noticeable.

Any expert photographers here want to comment?

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> > I always remember galactic vital statistics by knowing all the lyrics to this:
> >
> > http://en.wikipedia.org/wiki/Galaxy_song
> >
> > :-)
>
> Is that something like the song about the table of elements?

Similar, but more catchy ;-)

Post a reply to this message

>> Is that something like the song about the table of elements?
> 
> Similar, but more catchy ;-)

Heh. I still enjoy listening to TMBG exclaim that "the Sun is a mass of 
incandescent gas". ;-)

BUT EVEN WHEN IT'S OUT OF SIGHT THE SUN SHINES NIGHT AND DAY!

Post a reply to this message

http://en.wikipedia.org/wiki/File:Guisard_-_Milky_Way.jpg

Post a reply to this message

Invisible wrote:
> I can only presume this must be due to light pollution.

You need to go out someplace like 50 miles from the nearest street light. 
It's really rather overwhelming.

> Well, photons are quantum, right?

I'm not sure you'd see a point source. You need enough surface that the 
likelihood of multiple photons reaching your eye in a short interval is 
positive.

> (Interestingly, I'm told it *is* possible to make a light source that 
> emits individual photons, one at a time, on que. And that when you do 
> this, things like the double-slit experiment still show multiple waves 
> interferring and reinforcing - despite this being obviously 
> impossible... Wave-particle duality is weird!)

It's only impossible if you think the interference is caused by waves, which 
it isn't.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

Post a reply to this message

Invisible wrote:
> But where do you have to go? Outer Mongolia?

Most national parks in the USA are big enough.

> (Also... where the hell *is* that anyway?!)

Know how China has a concave top? In there.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

Post a reply to this message

Bill Pragnell wrote:
> I'd think it was a single shot. I bet you could get away with up to a minute of
> exposure, and it's very wide angle so any movement would be less noticeable.

You can also buy telescope tripods that will use a small motor to turn the 
telescope in counterpoint so the stars appear stationary. I imagine the same 
would work for a camera, and then it would be the ground that's blury.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

Post a reply to this message

Bill Pragnell wrote:
> I'm not sure. The fact that it's a nearly-complete panorama makes it even more
> complicated - I guess it must have been unwrapped from a fisheye.
> 
> I'd think it was a single shot. I bet you could get away with up to a minute of
> exposure, and it's very wide angle so any movement would be less noticeable.
> 
> Any expert photographers here want to comment?

Servo motors work wonders, when you can gear them correctly.

There are several tripod heads designed to track correctly against the
spin of the earth, allowing for long exposures. Anything that works for
for automatic telescopes can do the same work for a camera.

Or for cheap, a really long bolt, two pieces of wood, and a hinge. They
are called equatorial mounts or, for the cheapest ones, barn door trackers.

Post a reply to this message

>> I can only presume this must be due to light pollution.
> 
> You need to go out someplace like 50 miles from the nearest street 
> light. It's really rather overwhelming.

I don't know if any such place exists in the UK. Unless maybe you sail 
50 miles out to sea...

>> Well, photons are quantum, right?
> 
> I'm not sure you'd see a point source. You need enough surface that the 
> likelihood of multiple photons reaching your eye in a short interval is 
> positive.

I doubt your eyes can see single photons anyway...

>> (Interestingly, I'm told it *is* possible to make a light source that 
>> emits individual photons, one at a time, on que. And that when you do 
>> this, things like the double-slit experiment still show multiple waves 
>> interferring and reinforcing - despite this being obviously 
>> impossible... Wave-particle duality is weird!)
> 
> It's only impossible if you think the interference is caused by waves, 
> which it isn't.

Well, the books seem to claim that it *is* caused by waves, but they 
babble some nonesense about a "quantum superposition of states" to make 
up for the fact that this explanation makes no sense at all.

Post a reply to this message

Invisible wrote:
> This is awesomer:
> 
> http://en.wikipedia.org/wiki/File:Perseid_Meteor.jpg
> 
> Here in the name of God does the night sky actually look like this?!

Dunno, but now that it is cold I may have to find a map and make a
scouting expedition to find a place. City lights are annoying here, but
that picture looks like what I grew up seeing. Even there, the lights
are brighter at night, they finally put up street lamps, and the
neighbors leave their post lamps on, now.

But here, a half hour on the road will get me clear of the city and put
me in farm land. That's always a good start, with the side of a mountain
as a back up plan.

Post a reply to this message

> You can also buy telescope tripods that will use a small motor to turn the 
> telescope in counterpoint so the stars appear stationary. I imagine the 
> same would work for a camera, and then it would be the ground that's 
> blury.

That was my point, I know how to keep the stars sharp or to keep the ground 
sharp, but how to get both in the same photo?

Post a reply to this message

> City lights are annoying here, but
> that picture looks like what I grew up seeing.

I have never, ever, in my entire life, seen anything that remotely 
approximates this, except on TV and in posters. Every time I see 
something like this in films it looks like over the top CG, because real 
skies never, ever look like this.

It's quite impressive driving home, actually. By the time you reach 
Weedon, you can already tell where MK is because one entire side of the 
sky is bright orange. (I have no idea how far it is from Weedon to MK, 
but it's surely more than 10 miles.)

If you approach from the south, there's high ground that way. As you 
come down the hill, you can see the entire city laid out before you. It 
looks utterly huge. It seems to extend from one horizon to the other. 
(Obviously an effect of the terrain and it's slope.) And the entire 
thing is glowing.

I don't know about you, but when I look up at the orange horizon when 
I'm more than 10 miles away, I wonder what the HELL the council's 
electricity bill must be, and how much of the light we're paying for is 
leaking uselessly into the sky rather than illuminating the streets... 
Surely there's some more-efficient way to do this?

Post a reply to this message

scott wrote:
>> You can also buy telescope tripods that will use a small motor to turn 
>> the telescope in counterpoint so the stars appear stationary. I 
>> imagine the same would work for a camera, and then it would be the 
>> ground that's blury.
> 
> That was my point, I know how to keep the stars sharp or to keep the 
> ground sharp, but how to get both in the same photo?

Really, really friggin' BIG lenses, as a guess...

Apparently bigger lenses capture more light and generate better images. 
Seen any telescopes recently? Big, aren't they? ;-)

Post a reply to this message

> I'm not sure you'd see a point source. You need enough surface that the 
> likelihood of multiple photons reaching your eye in a short interval is 
> positive.

If the point source was emitting photons at the same rate as a star though, 
I don't think you'd be able to tell the difference between the star and such 
a point source.

Post a reply to this message

Invisible wrote:
> I have never, ever, in my entire life, seen anything that remotely 
> approximates this, except on TV and in posters. 

Like that line in Madagascar, when they're still in the New York Zoo.

"Oh, look, the star is out!"
"Whoops, nope, just a helicopter."

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

Post a reply to this message

Invisible wrote:
> I doubt your eyes can see single photons anyway...

Somewhere between 5 and 10 over the course of 100 ms, for humans.

> Well, the books seem to claim that it *is* caused by waves, 

Those books are wrong. It's the same *math* as waves, but it isn't waves.

> babble some nonesense about a "quantum superposition of states" to make 
> up for the fact that this explanation makes no sense at all.

It's only nonsense if you don't know what it means.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

Post a reply to this message

>> babble some nonesense about a "quantum superposition of states" to 
>> make up for the fact that this explanation makes no sense at all.
> 
> It's only nonsense if you don't know what it means.

"And the waves interact to generate these interference patterns."

"OK, so why do I still get the exact same patterns if there's only one 
photon there?"

"Um... right, OK... that's because there are these extra versions of the 
photon, that all exist at the same time. They generate the interference 
pattern. Oh, but you can't measure them, see? Because as soon as you 
look at them, they stop existing, right?"

"Dude... WTF?"

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> > City lights are annoying here, but
> > that picture looks like what I grew up seeing.
>
> I have never, ever, in my entire life, seen anything that remotely
> approximates this, except on TV and in posters. Every time I see
> something like this in films it looks like over the top CG, because real
> skies never, ever look like this.

Skies look like this in most places in the world (clouds and moon permitting, of
course!), considering how relatively sparse human population centres are. Just
think of all that ocean, too!

You can definitely see skies like this in many locations in the UK. You'll see
good skies within 50 miles of MK. But you do need to make the trip!

Post a reply to this message

Sabrina Kilian <ski### [at] vtedu> wrote:
> Bill Pragnell wrote:
> > Any expert photographers here want to comment?
>
> Servo motors work wonders, when you can gear them correctly.
>
> There are several tripod heads designed to track correctly against the
> spin of the earth, allowing for long exposures. Anything that works for
> for automatic telescopes can do the same work for a camera.

Yah... as Scott said, if it was done with a tracking mount then it must be a
composite, because both sky and ground are in focus.

I must try some sky photography sometime, though. :)

Post a reply to this message

scott wrote:
>> You can also buy telescope tripods that will use a small motor to turn
>> the telescope in counterpoint so the stars appear stationary. I
>> imagine the same would work for a camera, and then it would be the
>> ground that's blury.
> 
> That was my point, I know how to keep the stars sharp or to keep the
> ground sharp, but how to get both in the same photo?
> 
> 

With a camera, the trees are going to move relatively little if you are
tracking stars relatively high in the sky. And that little bit they move
will be hidden by the stars that take up the field of view where the
tree was before.

Tracking a star at the horizon would be more difficult. I would have to
think of a good trick there that doesn't involve just cropping or
zooming in on only stars.

Post a reply to this message

Invisible wrote:
> I doubt your eyes can see single photons anyway...

If the photon hits a rod cell in the eye, then yes. Whether the brain
would process this over the photon flux of your surroundings would be up
for question. In total darkness, I think you would see it.

Post a reply to this message

Sabrina Kilian wrote:
> Invisible wrote:
>> I doubt your eyes can see single photons anyway...
> 
> If the photon hits a rod cell in the eye, then yes. Whether the brain
> would process this over the photon flux of your surroundings would be up
> for question. In total darkness, I think you would see it.

It's true that in very low light conditions, vision takes on a 
"speckley" character, presumably due to some combination of small 
numbers of photons or small numbers of individual nerve impulses 
generating a fairly noisey signal. I'm not sure whether one single 
photon is enough to generate a nerve action potential though; maybe it 
takes 10 or so?

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Orchid XP v8 wrote:
>>> babble some nonesense about a "quantum superposition of states" to
>>> make up for the fact that this explanation makes no sense at all.
>>
>> It's only nonsense if you don't know what it means.
> 
> "And the waves interact to generate these interference patterns."
> 
> "OK, so why do I still get the exact same patterns if there's only one
> photon there?"

You don't get the interference pattern with only one photon. You get it
if you sum a lot of photons emitted one at a time. A single photon will
still hit only one place*, but that place is more likely to be in one of
the locations that you would expect from a wave.

Many-Worlds Interpretation not withstanding.

> "Um... right, OK... that's because there are these extra versions of the
> photon, that all exist at the same time. They generate the interference
> pattern. Oh, but you can't measure them, see? Because as soon as you
> look at them, they stop existing, right?"
> 
> "Dude... WTF?"
> 

Not quite the same, but how can a 4D object interact with it self in 3D
space?

Photons are not waves, but their position is governed by a waveform that
represents the probability that the particle will be at any given point.

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Orchid XP v8 wrote:
>>> babble some nonesense about a "quantum superposition of states" to 
>>> make up for the fact that this explanation makes no sense at all.
>>
>> It's only nonsense if you don't know what it means.
> 
> "And the waves interact to generate these interference patterns."

That's mistaken. There are no waves.

> "OK, so why do I still get the exact same patterns if there's only one 
> photon there?"

Because there are no waves.

> "Um... right, OK... that's because there are these extra versions of the 
> photon, that all exist at the same time.

That's an attempt to explain the interference patterns *assuming* photons 
are waves to start with. But they're not, so it's mistaken.

http://www.youtube.com/watch?v=_7OEzyEfzgg

Note that "amplitude" is the 2-D complex probability.  It's not that two 
photons get to the same place at the same time and cancel out.  It's that 
the photon just doesn't go there. Hence, no need for multiple photons to 
cancel.

What he's talking about at the end is things like, you know they're not 
waves because you only have two electrons in the innermost shell and you get 
lasers with bosons but not fermions.  I.e., you can't make an electron 
laser, only a photon laser. Hence, electrons aren't waves.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

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Sabrina Kilian <ski### [at] vtedu> wrote:
> You don't get the interference pattern with only one photon. You get it
> if you sum a lot of photons emitted one at a time. A single photon will
> still hit only one place*, but that place is more likely to be in one of
> the locations that you would expect from a wave.

  To put it more clearly:

  You don't need to send all the photons at the same time in order to get
the interference pattern. You can send photons one by one, with a significant
time interval between sending the photons, and you *still* get the exact
same interference pattern as if you had sent them all at the same time.
This means that a photon does not need other photons to interfere with in
order for the interference pattern to appear. A lonely photon traversing
through the double-slit will still present the same interference.

  I think that the vernacular interpretation is that the single photon
traverses as a wavefront and interferes with itself when it passes through
both slits at the same time.

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> Orchid XP v8 wrote:
> >>> babble some nonesense about a "quantum superposition of states" to 
> >>> make up for the fact that this explanation makes no sense at all.
> >>
> >> It's only nonsense if you don't know what it means.
> > 
> > "And the waves interact to generate these interference patterns."

> That's mistaken. There are no waves.

  It looks like a wave, it behaves like a wave, it produces all the effects
that a wave would produce, but it's not a wave.

> > "OK, so why do I still get the exact same patterns if there's only one 
> > photon there?"

> Because there are no waves.

  You get a wave interference pattern *because* (not "even though") there's
no wave. That makes sense.

  I wonder if the same principle could be applied to all non-intuitive
phenomena: The phenomenon happens *because* of what makes it non-intuitive,
not *regardless* of what makes it non-intuitive. Of course that claim is
quite non-intuitive all in itself.

-- 
                                                          - Warp

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On Mon, 30 Nov 2009 11:45:53 +0000, Invisible wrote:

>> There is nothing like spending a couple of hours on your back in a
>> field with a truly dark sky - it feels like there are far more than
>> mere thousands visible!
>> 
>> :o
> 
> But where do you have to go? Outer Mongolia?

You could probably see a fair bit from Stonehenge....For me, I'd probably 
have to travel about 30 miles up into the mountains (have done, actually, 
the night sky is quite cool to see from up on the eastern side of the 
mountains to the east of where I live).

As for where Outer Mongolia is, GIYF. ;-)

Jim

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On Mon, 30 Nov 2009 23:20:44 +0100, Orchid XP v8 <voi### [at] devnull> wrote:
>
> It's true that in very low light conditions, vision takes on a  
> "speckley" character, presumably due to some combination of small  
> numbers of photons or small numbers of individual nerve impulses  
> generating a fairly noisey signal. I'm not sure whether one single  
> photon is enough to generate a nerve action potential though; maybe it  
> takes 10 or so?

Not a bad guess.

http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html



-- 
FE

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Warp wrote:
>   I think that the vernacular interpretation is that the single photon
> traverses as a wavefront and interferes with itself when it passes through
> both slits at the same time.

Well, not really. The basic problem is people calling it an "interference 
pattern" to start with. It's not really "interference" as such, since 
there's only one particle. Calling it "interference" just encourages people 
to go looking for what wave is causing the interference.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

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Warp wrote:
>   It looks like a wave, it behaves like a wave, it produces all the effects
> that a wave would produce, but it's not a wave.

No, it doesn't. It has the same math as a wave, *if* there's only one. If 
there's more than one, the behavior isn't like waves.

What function of waves produces lasing? Polarization?

>>> "OK, so why do I still get the exact same patterns if there's only one 
>>> photon there?"
> 
>> Because there are no waves.
> 
>   You get a wave interference pattern *because* (not "even though") there's
> no wave. That makes sense.

No, you get the exact same patterns when there's only one photon there, 
because it's not caused by interference between photons.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

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Darren New wrote:
> No, you get the exact same patterns when there's only one photon there, 
> because it's not caused by interference between photons.

Actually, if you really want to push it, you could say the pattern is caused 
by interference between the two slits, not between multiple photons. That's 
why it changes based on whether you measure what goes thru the slits or not.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

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