100+ earth like planets dicovered.

Originally posted by twhitehead
Why? What would it require that we don't already have? Surely if it works for radio telescopes then it can be done for optical just as easily as soon as the optical scopes go digital? (which I assume they are already).

Actually no, we can combine the signals from radio waves digitally because the computers used have clock/sampling speeds way in advance of the frequency of light coming in and can actually measure the waves of light.
this information can be used to create a digital interference pattern.

In optical scopes, the detectors simply count number of photons coming in during exposure. they can't detect the subtle information needed to do interferometry.

This is why optical interferometers need to combine the light optically.

Originally posted by googlefudge
Actually no, we can combine the signals from radio waves digitally because the computers used have clock/sampling speeds way in advance of the frequency of light coming in and can actually measure the waves of light.
this information can be used to create a digital interference pattern.

In optical scopes, the detectors simply count number of photons ...[text shortened]... do interferometry.

This is why optical interferometers need to combine the light optically.

Bump

http://www.dailymail.co.uk/sciencetech/article-1287333/Scientists-use-worlds-powerful-digital-camera-hunt-dark-matter.html

Originally posted by mikelom
Bump

http://www.dailymail.co.uk/sciencetech/article-1287333/Scientists-use-worlds-powerful-digital-camera-hunt-dark-matter.html

and?

Just because the camera is digital (pretty much all optical cameras are and have
been for some time) doesn't mean they can be used for interferometry.

Originally posted by googlefudge
and?

Just because the camera is digital (pretty much all optical cameras are and have
been for some time) doesn't mean they can be used for interferometry.

I'm not arguing here, I'm probing only.

Why would a digitl cam telescope of 114 mega pix be exciting for looking into space/galaxies and receiving accurate colour pics that haven't been ventured before, in real time, to such accuracy?

They say so in the article, and it appears to be revolutionary to some extent, in their eyes..... so can you tell me why it isn't?

-m.

Originally posted by mikelom
I'm not arguing here, I'm probing only.

Why would a digitl cam telescope of 114 mega pix be exciting for looking into space/galaxies and receiving accurate colour pics that haven't been ventured before, in real time, to such accuracy?

They say so in the article, and it appears to be revolutionary to some extent, in their eyes..... so can you tell me why it isn't?

-m.

I wasn't saying it wasn't revolutionary, or useful.

The point of this camera is that it allows imaging of a wide angle at high resolution.

the fewer the number of pixels your camera has, the smaller the area of sky you
can image for any given desired resolution.

basically its like trying to get a clear picture of what's going on inside a room through
a tiny keyhole.
This camera lets you see more of the room at anyone time at a good resolution.

The colour aspect of it means that you can gain more information about the objects
you're looking at.

When looking for transient events such as supernova, it is useful to be able to image as
much of the sky as possible, so that you stand as high a chance as possible of seeing these
events. And of catching them as early as possible.

Interferometry, is more about looking at a very tiny patch of sky in extreme detail,
this is about looking at a large part of the sky in reasonable detail.

Originally posted by googlefudge
Actually no, we can combine the signals from radio waves digitally because the computers used have clock/sampling speeds way in advance of the frequency of light coming in and can actually measure the waves of light.
this information can be used to create a digital interference pattern.

Thats interesting. I thought the effect was quantum dynamic and interference could not happen 'digitally'.
Do you have any references on this, I am interested in learning more.

Originally posted by twhitehead
Thats interesting. I thought the effect was quantum dynamic and interference could not happen 'digitally'.
Do you have any references on this, I am interested in learning more.

heh, again you don't need the great quantum for this.


The idea of interferometry is that by taking light from two or more telescopes that are far apart you can
combine the light in such a way as to get the effect of a telescope the size of the separation of the scopes.
This simply uses the wave nature of light as described by Maxwell's equations.

With radio waves you can actually detect the waves coming in to the detector, and measure them.
Essentially what the waves are doing is making electrons move up and down in electric circuits and the
generated voltages/currents happen slowly enough on a big enough scale that you can take multiple readings
per wave and thus retain the ability to mathematically reconstruct it.

This gives you the information you need to do the maths inside a computer that creates the interference pattern.

http://en.wikipedia.org/wiki/Radio_telescope#Radio_interferometry

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

Originally posted by googlefudge
heh, again you don't need the great quantum for this.

Which is why I am getting confused here. My understanding is that the wave nature of light is entirely a result of quantum effects - and most importantly, goes away when a photon is detected. I understood that the two slit experiment would not work if the interference pattern was reconstructed digitally.

Originally posted by twhitehead
Which is why I am getting confused here. My understanding is that the wave nature of light is entirely a result of quantum effects - and most importantly, goes away when a photon is detected. I understood that the two slit experiment would not work if the interference pattern was reconstructed digitally.

Ok think about a basic radio wave detector.

My old analog bed side radio with a 3 foot stiff metal rod poking out the top.

The radio waves (oscillating electric and magnetic fields) are ploughing along through the 'ether' :-)
and encounter the tuned conductor that is my aerial.
The varying electric field in the waves induces the electrons to wave up and down in the metal
inducing currents and voltages that vary through time.

This varying voltage can be measured at intervals of much less than the period of the incoming waves
thus allowing a digital version of the wave to be created.

A telescope does the same thing with more accuracy.

I am not sure what you mean about reconstructing the two slit experiment digitally.

Originally posted by googlefudge
I am not sure what you mean about reconstructing the two slit experiment digitally.

If you did the two slit experiment, but used radio waves, and instead of a single screen, you had two separate screens, then performed the interference digitally, would you still get an interference pattern?
Would this not contradict the findings of quantum dynamics?

Originally posted by twhitehead
If you did the two slit experiment, but used radio waves, and instead of a single screen, you had two separate screens, then performed the interference digitally, would you still get an interference pattern?
Would this not contradict the findings of quantum dynamics?

What do you mean 'digitally'. I don't see how you could digitize such an experiment.

The wave/packet duality would seem to me to prevent such an experiment.

Originally posted by sonhouse
What do you mean 'digitally'. I don't see how you could digitize such an experiment.

The wave/packet duality would seem to me to prevent such an experiment.

Thats what I thought, but it seems to work for radio telescopes. I want to understand why.

Originally posted by twhitehead
Thats what I thought, but it seems to work for radio telescopes. I want to understand why.

Ah, I see your problem...

In the twin slit experiment the interference pattern is the photon interfering with itself after passing through both slits
(that's overly simplistic but you get the idea)

By measuring the photons coming through each slit individually you destroy the interference pattern as the photon
now only goes through one slit. [although there has recently been done a neat experiment where you do get to measure
which slit the photon goes through without destroying the pattern]

However in an interferometer you are not creating an interference pattern from one photon going through both telescopes.
each photon goes into one telescope.
you are interfering many photons with each other, not one with itself.

Originally posted by googlefudge
However in an interferometer you are not creating an interference pattern from one photon going through both telescopes.
each photon goes into one telescope.
you are interfering many photons with each other, not one with itself.

I still don't understand. My understanding was that all interference of photons was identical in nature to the two slit experiment. ie that the wave nature of light was entirely a result of photons interfering with themselves. The diffraction we are trying to avoid here is a direct result of that wave nature and also a self interference effect. Change the size of the aperture, and each individual photon is affected.

So how does bulk interference change things and why wouldn't it work in the two slit experiment?