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SETI just got €100mil to look for Aliens
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Speaking of telescopes, is it too early to get excited about the James Webb telescope? Supposedly scheduled for a 2018 launch, hopefully it doesn't get delayed again by too much. Will be brilliant to see what sort of extra detail it unveils.
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Great explanation, thanks for that It has served to remind me just how far away things are from us here
So the comment got me thinking, the two ways to make things visible are, build telescopes that resolve smaller things (mainly by increasing their 'size'), and look for the set of planets that are closest to us beyond our own solar system?0 -
That's a neat idea. It's the NEAT idea -- the "Nearby Earth Astrometric Telescope", proposed to the European Space Agency for launch sometime before 2025. The idea is to look for earth-sized planets around the 200 nearest stars to us that are of types similar to our own sun (F-, G-, and K-type).So the comment got me thinking, the two ways to make things visible are, build telescopes that resolve smaller things (mainly by increasing their 'size'), and look for the set of planets that are closest to us beyond our own solar system?
There is one caveat. I know it sounds from the previous discussion like you need bigger telescopes to resolve smaller objects, and that's true. But to detect the reflex motion of a star -- its sideways wobble due to the gravitational pull of a planet -- we just need to know its precise position. Counterintuitively, knowing its precise precision is not the same as being able to resolve it.
Here's why. Light is subject to diffraction, which is why a telescope -- no matter how good its focus -- shows a point source such as a star as a little disc surrounded by interference fringes. This Airy disc sets the limit of the resolution for an imaging camera: two distinct objects are said to be resolved only if the separation between them is at least the width of the Airy disc:
An explanation of diffraction and the Airy disc can be seen in the second picture above. Light waves which reflect off different parts of the telescope mirror interfere with each other. Wherever the waves intersect with path lengths which are an integer number of wavelengths, you get constructive interference and a bright fringe. At half-integer path lengths you get a dark minimum. The angular radius of the Airy disc is from its centre to the first minimum. Its diameter is twice this, and in radians or arcseconds (1 radian = 206,265 arcsecond) is given by:
where λ is the wavelength of the light and d is the aperture of the telescope. If we fill in λ = 500 nanometres for the centre wavelength of visible light, and d = 2.4 metres, we satisfyingly get 1/20 arcseconds which was the resolution we had for the Hubble space telescope's mirror. (You can do the same with the diameter of your pupil to get the resolution of the human eye).
Now, that's the angular width of the Airy disc. Suppose the disc is projected onto a screen or detector. What's its width, r, in metres? That obviously depends on how far the detector is from the mirror. If the detector is at the focus of the mirror then we are concerned with the focal length, f, and a tiny bit of trigonometry (plus the small angle approximation) gives:
Now, NEAT is only going to have a puny one-metre mirror and a focal length of 40 metres. That gives it a resolution of 1/8 arcsecond and an Airy disc radius of r = 24 micron. There'll be a CCD camera at the focus with pixels spaced 10 microns apart. (It's important for the pixels to be less than half the Airy disc radius to give what's called Nyquist sampling accuracy). This is where the seeming magic comes in. Although the Airy disc only spans a few pixels, several Airy rings can be taken together and all of the pixels can be analysed to calculate the exact centre of the Airy disc to an accuracy better than a millionth of a pixel. This gives the telescope a sub-microarcsecond accuracy, even though the resolution is vastly worse than this. We need good resolution for imaging, but only good accuracy for astrometry.
The fantastic accuracy is used to measure the angular distance between the target star and a number of reference stars. The reference stars are much further away so they don't have the same reflex movement that we're trying to measure in the target star. In order to have suitable reference stars in the field of view at the same time as the target star, you need quite a big detector area, given the average spacing in the sky between stars of appropriate brightness. Forty centimetres turns out to be the required width of the detector for NEAT, but it's infeasible to make a giant CCD chip of this size. Instead, the NEAT detector has multiple movable CCDs at the focal plane which are moved into position to see the reference stars while the central CCD spots the target star.
Now the problem becomes how to accurately measure the positions of all the CCDs with respect to each other. Here's where another piece of magic comes in. The main telescope mirror has a number of optic fibres around it, illuminated by a laser. These are a bit like artificial stars, but they are arranged to produce interference fringes on the CCDs at the focal plane that can be measured to calculate the exact (x,y,z) positions of the CCDs. The z position is important too, because the 40 metre focal length is maintained by flying two separate spacecraft in formation, one carrying the mirror and the other the detector. The spacecraft separation can only be maintained to about 2 millimetres accuracy, but this can be allowed for using the fibre optic metrology.
So that's it -- sub-microarcsecond accuracy for the nearest 200 sun-like stars allows us to calculate reflex motions caused by earth-like planets within their habitable zones (i.e. at 1 AU distance from the star).
Further reading:- NEAT page at Joseph Fourier University of Grenoble
- Malbet et al., "NEAT, An Astrometric Telescope To Probe Planetary Systems Down To The Earth Mass Around Nearby Solar-Type Stars", from proceedings of the 4th International Conference on "Spacecraft Formation Flying Missions & Technologies" held in St-Hubert, Quebec, Canada, on 18-20 May 2011 (Link)
- Malbet et al., "High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)", Experimental Astronomy, October 2012, Volume 34, Issue 2, pp 385-413 (Link)
- Chengxing et al., "Micro-pixel accuracy centroid displacement estimation and detector calibration", Proceedings of the Royal Society A, December 2011
Volume: 467 Issue: 2136 (Link)
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The Great Math Mystery (2015) [CC][HD] " Is math a human invention or the discovery of the language of the universe?The prime number component would be instantly spotted by any alien scientists or computers. All of the math stuff would be.
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That sounds reasonable, BUT ... if it's not a human invention then it must be somehow "real". What does "real mathematics" mean. Would it still be real if there wasn't a universe for it to describe? Some people (including clever ones like Roger Penrose) take this so-called Platonist view, although Penrose acknowledges that there's a bit of a paradox, which he calls the "three worlds problem":Cant watch it at work but Im going to go ahead and say its ridiculous to think its only a human invention, if we ever meet another species there's no way in hell they'll have gotten off their planet without advanced mathematics.
If mathematics exists independently, how does it give rise to the physical world it describes, which in turn produces beings like ourselves, who mentally conceive of mathematics.
An alternative view is that mathematics is "merely" the formal language with which we describe the regularities of nature, and has no independent existence. It stands to reason that we would have evolved to comprehend these regularities, since our success as a species depends on it. But there are two holes in that argument. It's not at all obvious that our survival depended on the high level of abstraction with which we now comprehend the laws of nature. And in any case, why should nature exhibit such deep regularities (aside, perhaps, from the anthropic principle)?0 -
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That sounds reasonable, BUT ... if it's not a human invention then it must be somehow "real". What does "real mathematics" mean. Would it still be real if there wasn't a universe for it to describe? Some people (including clever ones like Roger Penrose) take this so-called Platonist view, although Penrose acknowledges that there's a bit of a paradox, which he calls the "three worlds problem":
If mathematics exists independently, how does it give rise to the physical world it describes, which in turn produces beings like ourselves, who mentally conceive of mathematics.
An alternative view is that mathematics is "merely" the formal language with which we describe the regularities of nature, and has no independent existence. It stands to reason that we would have evolved to comprehend these regularities, since our success as a species depends on it. But there are two holes in that argument. It's not at all obvious that our survival depended on the high level of abstraction with which we now comprehend the laws of nature. And in any case, why should nature exhibit such deep regularities (aside, perhaps, from the anthropic principle)?
Can you please just post constantly?
I like your posts. 0 -
And then there are more esoteric physical theories that suggest the whole of physical existence is "informational" -- quantum field theory in which everything is associated with excitations of fields which are just "numbers in space", or the holographic principle which posits that the whole universe is just bits of information encoded on a surface. That may be what Max Tegmark is getting at in the video when he takes the view that the universe is maths.
I recall reading (somewhere) an argument that if you accept the following two premises:
a) It is possible for a species to create a simulated world filled artificial intelligences which would be unaware of the simulation.
b) Such a species would be likely to run many of these simulations for a variety of reasons - research, entertainment, curiosity, etc.
Then the probability suggests that we are more likely to live in one of the many simulated worlds than the one and only 'real' world.
Now obviously there are problems with just accepting those premises and there are probably even flaws in the logic of the argument (accepting premises based on our universe and applying them to an imagined one that would not necessarily follow the same rules), but it's interesting to think about for a while and then dismiss.
But then with your post above, it would almost make you wonder... 0 -
Hah! I just watched the video. I don't want to blow my own trumpet ... but my last two posts could've been the script for it.
Platonism -- check. Guest appearance by Roger Penrose -- check. Kronecker quote about god making the integers -- check. Natural occurrences of the Fibonacci sequence -- check. Surprising properties of the integers -- check. Queue of mathematicians saying they feel they are discovering maths rather than inventing it -- check. The "unreasonable" success of mathematics in physics -- check. Evolutionary adaptations that produced our mathematical abilities -- check. Alternative view about regularities in nature -- check. Square root of minus one -- ch ... uh, no.
That was a bit too mathematical. The one thing this program didn't have was much maths. They got as far as the inverse square law of gravity. Plus pictures of unexplained equations floating in mid air, which is always important in a science program. Stephen Hawking's publisher told him that he'd lose half his audience for every equation he put in his books. TV documentary makers have obviously decided that they can put equations in as long as they don't explain them ... just make them floaty and mysterious to underscore that this stuff is much too hard for mere mortals to understand. Pity. 0 -
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Yes, I remember coming across that one. (Can't remember if the hypothesis has a name?). Another one is called the Boltzmann Brain Paradox. This one requires you to accept that our comparatively low entropy universe is a random fluctuation embedded in a higher entropy universe. Another way of thinking about it is that in a Big Bang Universe evolving toward higher entropy, you are much more likely to find yourself in the infinitely long high entropy tail than the low entropy initial stages.Maximus Alexander wrote: »I recall reading (somewhere) an argument that if you accept the following two premises:
a) It is possible for a species to create a simulated world filled artificial intelligences which would be unaware of the simulation.
b) Such a species would be likely to run many of these simulations for a variety of reasons - research, entertainment, curiosity, etc.
Then the probability suggests that we are more likely to live in one of the many simulated worlds than the one and only 'real' world.
Now obviously there are problems with just accepting those premises and there are probably even flaws in the logic of the argument (accepting premises based on our universe and applying them to an imagined one that would not necessarily follow the same rules), but it's interesting to think about for a while and then dismiss.
But then with your post above, it would almost make you wonder...
The most likely form of life in a high entropy universe is a level of organisation that arises spontaneously as a random fluctuation -- all the elements required to form sentience just randomly come together, no matter how briefly, to form a so-called Boltzmann brain. Such fluctuations are incredibly rare, yet must still happen infinitely often.
Since they happen infinitely often they happen much more often than a) the singular occurrence of the low entropy early universe, b) a late random fluctuation that results in our entire local part of the universe with all its evolved galaxies, stars, planets and people.
Therefore, it's more likely that you are an isolated Boltzmann brain that has spontaneously formed, complete with all your memories of growing up in an evolved world with billions of other people in it. It's a bit like your simulated world in that your entire perception of the world is an illusion, except in this case the simulation is a random thermodynamic fluctuation instead of the creation of an intelligent agent.0 -
Maximus Alexander wrote: »Can you please just post constantly? I like your posts.
Checks Astronomy forum
Sees new post by ps200306
YayYes, I remember coming across that one. (Can't remember if the hypothesis has a name?). Another one is called the Boltzmann Brain Paradox. This one requires you to accept that our comparatively low entropy universe is a random fluctuation embedded in a higher entropy universe. Another way of thinking about it is that in a Big Bang Universe evolving toward higher entropy, you are much more likely to find yourself in the infinitely long high entropy tail than the low entropy initial stages.
The most likely form of life in a high entropy universe is a level of organisation that arises spontaneously as a random fluctuation -- all the elements required to form sentience just randomly come together, no matter how briefly, to form a so-called Boltzmann brain. Such fluctuations are incredibly rare, yet must still happen infinitely often.
Since they happen infinitely often they happen much more often than a) the singular occurrence of the low entropy early universe, b) a late random fluctuation that results in our entire local part of the universe with all its evolved galaxies, stars, planets and people.
Therefore, it's more likely that you are an isolated Boltzmann brain that has spontaneously formed, complete with all your memories of growing up in an evolved world with billions of other people in it. It's a bit like your simulated world in that your entire perception of the world is an illusion, except in this case the simulation is a random thermodynamic fluctuation instead of the creation of an intelligent agent.
Mind = blown0 -
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Just to round out the discussion of long baseline interferometry: at much longer wavelengths -- microwave and radio wavelengths -- the combining can be done electronically, so the size of the effective aperture is practically unlimited. Radio telescopes have been combined to give effective apertures thousands of miles long. Although the longer wavelength reduces the resolution, it is still possible to achieve micro-arcsecond resolutions. Proposed space-based arrangements would do even better, and this has been tried experimentally. As with optical telescopes, you still need large dishes/mirrors to see faint sources.
I was reminded of this again when I read this about VLBI (Very Long Baseline Interferometry) at the EHT:
http://physicsworld.com/cws/article/news/2015/dec/04/magnetic-fields-near-the-milky-ways-black-hole-seen-for-the-first-time
The Event Horizon Telescope was so named because one of its goals was to resolve details close to the event horizon of the Milky Way's central black hole. The VLT may be able to see a tennis ball on the ISS, but the EHT can see an orange on the moon! :pac:
They achieved a resolution of 15 microarcseconds to see structure in the polarisation of microwaves that indicates a strong magnetic field ... which is what has long been hypothesised to be driving the bipolar jets we see emerging from active galactic nuclei.
Long newspaper article on the EHT here:
http://www.nytimes.com/2015/06/09/science/black-hole-event-horizon-telescope.html?_r=1
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The boards.ie SETI team is always open for more members!
Download for BOINC - select SETI@Home when setting it up after install.
http://boinc.berkeley.edu/download.php
Then join the team
http://setiathome.berkeley.edu/team_display.php?teamid=30742
If you know a few things about GPUs and have one that can do calculations then run the lunatics advanced installer here:
http://lunatics.kwsn.info/index.php
You`ll get far more processing power.0 -
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https://www.youtube.com/watch?v=pPUTrIgdCZI
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