SETI

There is no extraterrestrial signal from space

gregladen — Tue, 30 Aug 2016 11:25:48 +0000

There is no extraterrestrial signal from space

Sometimes I think there are not abundant intelligent life forms wafting about the universe. We would see things in our careful, highly accurate, detailed looking at a sampling of the universe. But, I suppose we've only been scanning with super amazing instruments for a few years, and only scanning a small fraction of the universe. But certainly, in a decade or two we'll be able to say that radio-communicative or emitting intelligent life is either out there somewhere, or not likely to be. Absence of evidence will evolve into evidence for pessimism, at the very least.

Meanwhile we get these little quirks. And, the latest is a burst of radio-info that the experts on this all seem to be saying is not a thing, looks like lots of other things that are also not things, but one guy somewhere put out a press release so now everybody thinks it is a thing.

But it is not. Not a thing. Nothing.

gregladen Tue, 08/30/2016 - 07:25

Tags

Cosmos

Not ET

SETI

Cosmos

Let's keep things in perspective. We have a pair of spacecraft that are now more than 100 AU away, which are still communicating with us here on Earth.

Think of these as "alien life forms transmitting an intelligent signal" in our direction. (The Voyager spacecraft are certainly "alien" to most human beings.)

How strong is the signal coming from them? We're still able to pick up their signal, but only at a VERY low bit rate -- much slower than the LEO spacecraft that "we're using every day". Much, much slower.

Putting that aside, the signal strength here on Earth, as we receive it, is about 1x10(-16) Watts. That's "incredibly weak" -- by an standard.

So, 1x10(-16) Watts for "an alien signal" being sourced at 20 Watts from a distance of 100 AU.

The nearest star is 4.24 light years. One LY is about 63200 AU. That's 632x farther away than Voyager. Will the signal be 632x weaker if Voyager were at Proxima Centauri? No...

Signal strength falls off as r-squared. We can estimate, then, that Voyager's signal would be 1/400,000x as strong. Just to maintain the same received signal strength, it's transmitter would need to be 400,000x more powerful: 8 megawatts.

That's a hefty amount of power to put on a spacecraft, but let's say that it's a ground-based transmitter on a planet around Proxima Centauri. Let's further make it easy on ourselves and wave our hands and ignore the huge source of noise just next to it, the star itself...

In order to receive the signal from Voyager at 100 AU, we have to use the largest antenna we have: One of the 70-meter antennas of NASA's DSN. This means, by implication, an antenna with very high gain...

The problem with using antennas that have very high gain is that their beam width, i.e., the area of the sky they're "listening to" is very small. The higher the gain, the smaller the area.

This has another important implication: You had better know, with exquisite detail, exactly where to point your big antenna in the sky, or you'll miss the signal entirely. Entirely. As in "no signal at all".

Worse: Your source is moving... Even if it is a planet and not a spacecraft. Worse yet: Your antenna is moving -- fast (by comparison). You now need to be able to point your antenna with great precision and keep it tracking your source with great precision, too -- or you loose your signal.

The DSN has a tough job -- even for something as close as 100 AU...

But what are the chances of an alien being as close as 4.2 LY? Not much. After all, the Russian signal was from a source 95 LY away. 95/4.2= 22x farther away. But that means a signal that's 500x weaker again.

Better make that alien transmitter 4 GIGAwatts.

Oh, and another confounder... That 4 GW transmitter? It has to also be part of a very high gain antenna, otherwise, more watts... (4 GW will power several good- sized cities on Earth. These aliens had better have some good justification for that kind of electricity bill...)

More troubles: That alien high-gain antenna pouring 4 GW of signal had better being pointing EXACTLY at Earth... the ENTIRE time it's transmitting. It has the same tracking issues that our DSN antennas have: You have to track your s/c in the sky just as accurately while transmitting to it as you do when receiving its signal.

The odds that an alien civilization "out there" would build and power a super-high-powered antenna and decide to track & broadcast to us, specifically? Because if they're not pointing right at us, we're getting nothing.

As Greg says, "But it is not. Not a thing. Nothing." Sorry.

Because if they’re not pointing right at us, we’re getting nothing.

They can avoid this limitation by broadcasting over the full 4π steradians, but as you note, this would require a proportionate boost (several orders of magnitude depending how tightly beamed the signal is) in transmitting power. Traditional broadcast radio and TV signals use this method because they want their signal to be received by many different people in all directions (at least azimuthally) from the broadcast tower. But the most powerful such stations have transmitting powers of the order of 100 kW. Communications and navigation satellites also use this method because they want the signals to be picked up in wide enough angular region that they may as well broadcast to the full 4π steradians. But that's far less than what you can do with ground-based transmitters.

Suffice to say that the alien civilization that can afford transmitters that are that powerful is almost certainly way beyond us in technology.

So, if there were another civilization somewhere out there, and they
a) were sufficiently advanced to be able to design communication systems as powerful as needed to get a meaningful signal here
b) had the resources and time to devote to building those systems

what, exactly, would be their point? If they were advanced enough to consider such an action, isn't it likely they would be advanced enough to be able to explore their local space (to a greater extent than we have ours) and know that travel to systems like this one isn't really feasible? It would seem that mounting a mission from there to here would require so much technology and time that it would be judged impractical.

#3 Dean - in addition they had to have existed at that stage of advancement at a time when their signal would be receivable by us x light years in the future, we have to be looking in the right direction at that time and with equipment capable of receiving it. If as a life-form they are anything like us there is a high chance they will kill themselves off near the time they reach that level of advancement so the window of opportunity here will be very small. I suspect that if the universe is filled with alien civilization many have died out, many are not interested in, or physiologically incapable, of pursuing technology in that direction, many have not reached that level of maturity yet, and lots more "manys".. Maybe they are all out there scanning the skies for someone else to communicate with them first - who will blink first :)

That's touching on another confounder I didn't mention: In order to have a communication (including mere 'detection'), the transmitting group has to transmit "at something", and do so in co-ordination with the receiving group looking directly at the transmitter at the same time (with the expected adjustments for time-of-flight).

For JPL, this means having precision clocks on Earth and the spacecraft, tightly synchronized. And careful navigation predicts so that we know where the s/c will be at time T, and how it will move in the sky over the transmission period. On the spacecraft, it has to similarly know where earth will be during the reception period in order to point its antenna.

And then both have to know when the signal is/is to be airborne, so that the s/c and ground are receiving/transmitting in co-ordination with each other. No point in listening if you tune in after the signal is gone.. or listen too soon (and then it goes "over the horizon").

Not to mention that both sides have to have a carrier frequency agreed upon. And a data modulation scheme that's also pre-determined. (Not done yet...) And they have to agree on the data rate that's being modulated.

Sorry, but it gets worse! Since the sender & receiver are moving with respect to each other, the frequencies of the signals are changing too -- doppler effect. So either the transmitter must pre-compensate its transmission frequency so that a constant frequency is received on the other end, or the receiver must be able to track the change in the received signal -- but it has to know where to start. And when. (Voyager 2 has to use the first technique; its receiver lost most of its tracking bandwidth when its loop capacitor shorted out.)

So you require:
High (enough) gain antennas,
High (enough) transmit power,
Precision pointing of the transmitter antenna,
Precision pointing of the receiver antenna,
Matching carrier frequencies,
Matching data modulation schemes,
Matching data rates,
Synchronized clocks,
Pre-agreement on session start time,
Predicts for doppler compensation,
--and for the high gains required--
Predicts for navigation to aid pointing and tracking.

Get any of those wrong and you get NO SIGNAL. Given the distances involved, there is no technology that will allow you to broadcast low gain with a compensating power boost suggested by Eric to reduce the pointing requirements. (The current maximum that NASA can transmit is about a megawatt -- nowhere near interstellar needs. Higher than that and you melt the waveguides...)

nowhere near interstellar needs. Higher than that and you melt the waveguides…)

No problem. All ET needs to do is build a dyson artifact with a big gap in it. A quick bodge-up of a stellar lighthouse! A solar system's worth of material resources would probably be required, but think of the dividends.

Some tens, hundreds or thousands of years later, the blinkety-blink is detected here, on Earth.

What a payoff!

"It was a quiet night in the galaxy, not a signal to be found..."

We are going to detect intelligent life on other planets using something other than radio signals.

It will probably be an isotopic signature.

It will probably be an isotopic signature.

Even there, you have to watch out for natural confounders. There are acceleration processes in interplanetary space that are known to modify isotope ratios, particularly 3He/4He and 22Ne/20Ne (presumably others as well, but those are two of the easiest to measure). The 3He/4He ratio in particular can change by several orders of magnitude, so it might be possible to detect these processes with a sufficiently powerful spectroscope (the frequency of certain spectral lines will be shifted slightly due to the different mass of the nucleus--this effect has been observed in the lab for deuterium vs. hydrogen in the lab, but the processes in question don't change the D/H ratio very much).

There are also processes that affect the 13C/12C and 18O/16O ratios in biological systems. These processes are correlated with temperature, so they are sometimes used as proxies for paleoclimate. But these changes are at the parts-per-million level, so they would be hard to detect at stellar distances. And even if they were detected, it would only mean that there was life on some planet in that stellar system, not that it was intelligent.

My hunch, based on the Fermi Paradox and Earth's previous geological and palaeontological history, is that life maybe relatively common in the cosmos but highly "advanced" technological sentiences like ours may be very few and far between. I'd love to be proven wrong though!

Meanwhile in somewhat related news; that new found Proximan planet is an amazing and wonderful discovery indeed - but with a range of planetary temperatures from minus thirty three* to the "high hundreds" in degrees Celsius suggested in an article in the latest New Scientist magazine (pages 8 & 9, Jacob Aron, 27th August 2016** ) calling it earthlike is a bit misleading! It could be frozen solid apart from the odd blast of extreme radiation by the Proximan flare winds or similar to Venus depending on atmospheric details. It could also be a world that's carbon rich - with an ashphelt surface over diamond core like 55 Cancris e , could be all ocean or had most of its atmosphere blasted away resembling a super sized Mercury or be the stripped down core of a gas or ice giant or .. ??? We don't yet know. Sure fun to speculate but have to conclude we've insufficient data as yet - and must therefore learn more.

* That's minus twenty seven point four Fahrenheit according to an online converter thingammyjig.

** * Despite that range and unknowns this article is headlined "The Earth next door" which strikes me as being rather misleading and poor journalism.

Kickstarting WTF star monitoring

catdynamics — Fri, 10 Jun 2016 21:53:13 +0000

Kickstarting WTF star monitoring

Tabby's Star - KIC 8462852 - remains one of the more interesting and mysterious objects in the sky.

There is a good update at "Updates on Boyajian’s Star" - Astrowright's blog and "Bradley Schaefer: Further Thoughts on the Dimming of KIC 8462852" at Centauri Dreams has the latest on the controversy over whether the star has undergone long term fading.

Update: "The Most Mysterious Star in the Galaxy" - another guest blog by Schaefer providing a good overview of the issues.

Ultimately to resolve this more data is needed.
There is a Kickstarter Project - "The most mysterious star in the Galaxy" - to get serious time on Las Cumbres Observatory, the request is almost 2/3 of the way there with a few days to go.

Kick in if you can!

"Planet Hunters X. KIC 8462852 - Where's the Flux?" - Boyajian et al.

catdynamics Fri, 06/10/2016 - 17:53

Tags

Are We Alone In The Universe? Explore Answers With Nifty Fifty Speaker and Noted SETI Astronomer, Dan Werthimer

carlyo — Thu, 21 Aug 2014 08:00:45 +0000

Are We Alone In The Universe? Explore Answers With Nifty Fifty Speaker and Noted SETI Astronomer, Dan Werthimer

The ‘Nifty Fifty (times 4)’, a program of Science Spark, presented by InfoComm International, are a group of 200 noted science and engineering professionals who will fan out across the Washington, D.C. area in the 2014-2015 school year to speak about their work and careers at various middle and high schools.

Meet Nifty Fifty Speaker Dr. Dan Werthimer

The great debate continues: Are we the only intelligent life in the universe? We know that popular science fiction often portrays our Milky Way Galaxy as teeming with advanced civilizations engaged in interstellar communication, commerce, and occasionally star wars. But extraterrestrial life has proved elusive. None has yet been found.

However as arguments for and against technological life in the Galaxy sharpen, noted astronomer Dan Werthimer and his colleagues at the world-renowned SETI Research Center at the University of California, Berkeley (SETI is short of "Search for Extraterrestrial Intelligence"), are becoming increasingly optimistic of the possibility of extraterrestrial life.

Dan is principal investigator of SETI@home and several radio and optical SETI programs at the University of California, Berkeley. Testifying in May 2014 before Congress with fellow SETI scientist Seth Shostak on the need for continued federal funding for SETI and related institutions nationally, Dan said that research at the SETI is suggesting positive signs toward other life in the universe, and that he thinks the possibility of microbial life on other planets is close to 100 percent.

Dan added that he is not advocating reaching out to alien life forms, but instead, he said that we should just "receive signals and see what's out there,"adding,"My feeling is that we should just be listening."

In SETI's mission to detect intelligent life outside Earth, Dan plays a key role by using technology known as radio SETI, which employs radio telescopes to listen for narrow-bandwidth radio signals from space. Such signals are not known to occur naturally, so a detection would provide evidence of extraterrestrial technology.

At SETI, Dan also directs the Center for Astronomy Signal Processing and Electronics Research (CASPER), and is associate director of the Berkeley Wireless Research Center (BWRC).

Before coming to SETI, he was associate professor in the Engineering and Physics
Departments of San Francisco State University and a visiting professor at Beijing Normal University, the University of St. Charles in Marseille, and Eotvos University in Budapest.

Dan has taught at universities in Peru, Egypt, Ghana, Ethiopia, Zimbabwe, Uganda and Kenya. He is co-author of "SETI 2020", editor of "BioAstronomy: Molecules, Microbes and Extraterrestrial Life" and of "Astronomical and Biochemical Origins and the Search for Life in the Universe".

carlyo Thu, 08/21/2014 - 04:00

Tags

USA Science & Engineering Festival

How Alien Can a Spacefarer Be?

milhayser — Wed, 16 Jul 2014 06:56:17 +0000

How Alien Can a Spacefarer Be?

As our planet makes more and more noise, we can't help but wonder why no one is paying attention. Are we alone in the universe? Or alone in our desire to discover new worlds? PZ Myers says "Spaceship building is never going to be a selectively advantageous feature — it’s only going to emerge as a spandrel, which might lead to a species that can occupy a novel niche." Humanity could tread that path, following our dreams to the stars. But even then, we might only find extraterrestrials in the form of well-adjusted slime blobs, content in their otherworldly ecosystems.

If there are other tech-savvy lifeforms in the galaxy, would they communicate with lasers instead of radio waves? This could explain our apparent isolation, because the civilized worlds are narrow-beaming communications to their neighbors and leaving us in the dark. Chad Orzel explains how it would work, with a possible assist from a 'magic compact fusion reactor.' That device is still on our to-do list.

milhayser Wed, 07/16/2014 - 02:56

Tags

Misc

Fermi Paradox

Fusion

Interstellar Communication

Lasers

SETI

Xenobiology

Yes, yes, and no.

Yes they are probably using lasers between their various inhabited worlds (or they've invented the Ansible;-), because ordinary RF is terribly inefficient at interstellar distances.

Yes they are probably ignoring us, or perhaps they're still deciding if we're too dangerous to contact.

But no, I'll have to differ with PZ about selection utility.

Compared to the estimated future lifespan of the observable universe, Earth life is barely in its infancy. Any life-bearing planet will eventually face extinction as a function of the life cycle of its home star. For example in approx. 1/2 billion years, the Sun's luminosity will increase to the point where Earth's carbon cycle is disrupted and the oceans boil. Nothing will survive that except possibly some isolated extremophile bacteria.

But if we succeed in becoming an interstellar civilization, the lineage of Earth life will continue beyond the loss of Earth itself. Having made the jump to a new star system once, we will be able to keep doing it until Earth-originated life inhabits a number of other planets in our region of the galaxy.

The more planets we occupy, the more resilient we are against the loss of any of those planets.

The mechanisms are the same as applied when humans spread from Africa to the rest of the globe: any local catastrophe might take out a subset of the whole, but the species would continue.

That is a selection advantage, in the same manner as building canoes and sailing ships was a selection advantage in the past.

The fact that Earth-originated life will diverge in various ways over time, does not invalidate the premise.

This is Darwinian selection on the cosmic scale, over a span of potentially trillions of years.

New Frontiers: the second day

catdynamics — Wed, 18 Jun 2014 07:26:31 +0000

New Frontiers: the second day

Day two of the New Frontiers wrap-up conference. This is a slow liveblog with more cosmology and life in the universe. Yesterday's summary is here

A couple of years ago, the Templeton Foundation funded the New Frontiers program to pose "Big Questions" in some areas of science.

This is a slow liveblog - part II will be tomorrow with more cosmology and life in the universe

Seed funding was provided to 20 investigators and small groups to start exploratory research, and, now, it is time to say what they found.
This follows up from the New Frontiers kick-off conference back in 2012.

We start the morning with some more cosmology before going to alien life after lunch.

Measuring the Multiverse: Raphael Bousso (UCB)
Continuing from where Aguirre left off, with some background intro on the cosmological constant leading to eternal inflation and the string landscape.
Most bubble vacua have large cosmological constants, small horizons, few internal quantum states and no observers - anthropic bias.
Qualitative difference to get an interesting enough universe for there to have been a phase transition with reheating.
Old school "one dimensional" multi-vacua multiverse falsified (I think this is a very theorist use of the word "falsified", but fair enough).
Time emergent from entropy increase
long term single vacuum de Sitter with T ~ √ Λ
- digression to Boltzman brain problem
multi-vacua avoids this if vacuum decays faster than it spawns brains.
Testing the Multiverse with Cosmic Bubble Collisions: Matthew Kleban (NYU)
Very good overview of phase transitions and bubble production.
Is the multiverse testable? Well, yes, duh...
Look for:
- positive curvature - multiverse predicts negative curvature
- low power in scalar fluctuation at low multipoles
- bubble collision signatures
looked at alternative picture for bubble formation - repeated bubble collisions in extra dimensions to drive slow roll inflation - hmmm

Stringy, toy model does fun stuff with quantitative predictions in interesting range.
Testable predictions.

Inflation from Flux Cascades

Guido D'Amico, Roberto Gobbetti, Matthew Kleban, Marjorie Schillo
Journal of Cosmology and Astroparticle Physics, Issue 11, article id. 013, pp. (2013) (arXiv)
CMB Polarization, 21cm cosmology and testing the multiverse: Chao-Lin Kuo (Stanford)
Nice intro on polarization and scattering
Quick summary of BICEP2 3 year result, decomposing into E and B modes, claim 5+ σ detection of B modes.
Big question is whether it is coming from CMB or foreground, of course.
Definite lack of power at low multipoles, especially around l ~ 20-30
Is this a sign of inflation? (see Bousso et al. arXiv:1404:2778)

Is polarization due to dust foreground? TBD
Planck data release + Keck Array + BICEP3 will determine in near future.

So, the CMB people are not talking enough to the galactic dust people, because my impress is that a lot more was known about foreground dust than they think, even if there were not global maps of high precision polarization fraction.
Low intensity dust emission tends to have high polarization fraction...

Interesting overview of future prospects.
Search for drifting constants via extra-galactic alcohol: Wim Ubachs
Are constants constant?
Test by looking at observables at different times in universe.
Was Leibniz or Voltaire right?
Looking at ratio of electron mass to proton mass. Existing limits are changes by less than 10 parts per million over last 10 billion years, based on UV spectra.
Looking at methanol to get better sensitivity.

Robust Constraint on a Drifting Proton-to-Electron Mass Ratio at z=0.89 from Methanol Observation at Three Radio Telescopes

Julija Bagdonaite (1), Mario Daprà (1), Paul Jansen (1), Hendrick L. Bethlem (1), Wim Ubachs (1), Sébastien Muller (2), Christian Henkel (3,4), Karl M. Menten (3) ((1) VU University Amsterdam, Netherlands (2) Onsala Space Observatory, Sweden (3) Max-Planck-Institut für Radioastonomie, Germany (4) King Abdulaziz University, Saudi Arabia) Physical Review Letters, vol. 111, Issue 23, id. 231101 (arXiv)

Constraint improved by 2 orders of magnitude.

Also looked ad GD-133 using COS to look at Ly absorption to look for equivalence principle violations, dependence on gravitational potential dependence.
Also looking at GD29-38
Got limits on equivalence principle violation at 50 ppm level. Not bad.
Global structure of the multiverse and the measure problem: Alexander Vilenkin (Tuft)
Sorry, missed this one.
Lots of discussion on whether we can define "beginning"...
----Lunch break----

and we are back:
The search for life in extremely exotic environments A strict test for life's cosmic ubiquity: Jonathan Lunine (Cornell)
Looking at Titan, natch.
Interesting discussion on H-bonding at low temps in ethane/methane solvent.
Cyanogenic polymers.Molecular dynamics/mechanics sims to look into assembly - made "azotosomes" - spherical self assemblies, not known if stable, yet.
Also self-assembling monolayers and helical polymers. Polyacetylene for light harvesting?
Look potentially interesting.

Cassini saw large transient features in the seas on Titan - could be something interesting "growing" - comes out next week.
Discovery of Earth-like Planets and Signals from Intelligent Life: Geoffrey Marcy (UCB)
Looking for coherent optical emission with the Keck Telescope, and looking for Dyson spheres in Kepler photometry.
Begins with overview for cosmologists of state of exoplanet discovery.
State of exoplanet discovery is awesome.
There are lots of exoplanets, especially nice little ones.

Can see 100W lasers to 10 pc or so - have couple of interesting looking candidates with ~8 σ emission - should be looked at further.
Stellar Lighthouses: Decoding Signatures of Advanced Civilizations in Precision Stellar Photometry: Lucianne Walkowicz (Princeton)
Overview of Kepler photometry and modern ultrahighprecision stellar photometry.
Can do stuff other than just find planets with time series photometry like that.
Pick up stellar variability; flares, stellar spots, pulsations, as well as transits.
Also can do very good asteroseismology.

Very large data sets, look for unknown kinds of signals using machine learning - specifically unsupervised learning.
Clustering and looking for outliers

Finding new heartbeat stars and some interesting new variables, including very rapid rotators with strong flares.

Couple of WTF variables - one which turned out to be a diffraction spike rotating with spacecraft reorientation...
a couple of the others do look very interesting, but they also look stellar, not naively artificial
Constraining the Abundance of Kardashev Type II and III Civilizations From Large Area Infrared Surveys: Jason Wright (PSU)
Background on Kardashev scale and concept of categorizing civilizations by energy use (not intended to be a normative description - just a prescription).
Discussion of time scale to convert from KII to KIII - argument for why once you can spread to adjacent stars spread across galaxy is rapid compared to galaxy lifetime.

Ought to look both for galaxy spanning civilizations in other galaxies and KII civilizations in the Milky Way - low effort search worth while at this stage as secondary to other surveys.

So we did.

Discussion of artifact transit and KIC12557548 - per request from Marcy and Walkowicz - it is a mystery

WISE catalog - filtered high galactic latitude extended red sources
have a 30,000+ interesting candidate very red sources -
looked at the 4,000 best sources to classify them

Split them into already know sources; garbage and ghosts; and new very red sources that could use a closer look.

Students start this week at SETI institute to do followups.

Out of 10⁵ resolved WISE sources in local universe less than 1,000 are consistent with having significant KIII coverage, and most of those are known starburst or merger galaxies - so we can put strong constraints on fractional abundance of KIII or even partial KIIIs in local universe.
Can push limits down a lot further with modest effort, dust modeling, look at few thousand more candidates, chase down still unknown sources.

Next step is cross-correlate with GAIA catalog - particularly good for filtering KII sources in crowded low galactic latitude regions.

On thing mentioned by several speakers is that we are not far enough a long for a lot of the projects - the projects are all nominally 2 years, and funding commenced about 21 months ago, but that effectively meant that most started serious efforts about 18 months ago, and so many only have preliminary results or "in prep" results.
There's a reason a lot of astro/physics projects operate on three year cycles.

catdynamics Wed, 06/18/2014 - 03:26

Tags

New Frontiers: the first two years

catdynamics — Tue, 17 Jun 2014 07:49:36 +0000

New Frontiers: the first two years

A couple of years ago, the Templeton Foundation funded the New Frontiers program to pose "Big Questions" in some areas of science.

This is a slow liveblog - part II will be tomorrow with more cosmology and life in the universe

The New Frontiers conference to report the hint of the beginning of the draft of the answers is under way... most of the investigators and about half of the student prize winners are here for a couple of days of fairly intense talks and discussion of the progress to date.

@shaka_lulu is tweeting #newfrontiers

Fossil Remnants of the Universe's Beginnings: David Chernoff (Cornell)
Look for Cosmic Strings - predicted from inflation plus some guesstimates for phase transitions and and actual theory of strings.
Can be observed in principle - eg through lensing, ought to be finite number of cosmic string loops locally, be interesting to observe to see if we can measure physical parameters eg. string tension.
Model for reasonable theory parameters to see if likely to see string lensing in current or near future surveys.
Short answer: PanStars may see something with a bit of luck; WFIRST ought to see something IF assumptions are correct.
CosmoArcheology: Richard Holman (CMU)
Looking for "initial state" of universe. CMU team + Sarah Shandera (PSU).
Only looking as far as inflation...
Testing independent/gaussian etc, hoping to look at tensor modes, but caveat BICEP2 - more on that later ~~maybe~~ - ah yes, Kuo is here - definitely more on BICEP2 tomorrow.
Taking inflation generated quantum modes and mapping them to power spectrum to test allowed initial inflationary states.
More data constrains inflationary models.
Will either find consistent set of inflationary states, or not. (the magic word here is Bunch-Davies vacuum).
Important either way. Cute way of doing this.
Computing the Wavefunction of the Universe: Kostas Skenderis (Southampton) talking for Alexander Maloney (McGill) - Hartle-Hawking formalism, Wheeler-de Witt equation, using de Sitter/Conformal Field Theory conjecture to get some pieces for the ground state wavefunction
Compute Ψ(h) at future timelike infinity - toy model - anti-commuting, mass-less, non-interacting scalar field under Sp(N). Conformally invariant, natch. High spin excitations.

Result: might be generic - favours topologically complex space times, more degreees of freedom with more complex topologies.
Ought to be generic to holographic theories - that they favour complex topologies.
Interesting if true.

Good job giving someone else's talk at zero notice!
Probing the genesis of spacetime using supercomputers: Parampreet Singh (LSU)
Toy model numerical quantization of homogenous spacetime using quantum loop gravity.
Looking at generic singularity avoidance, evolution of perturbative anisotropies etc.
Generic behaviour: see sub-planckian bounce before singularity - seen in localized gaussian states at ρ ~ 0.41 - in suitable units - robust critical density value.
End up with cyclic universes.
Very interesting if physical.
Speculative claims: generic spacetimes - can transition from AdS to dS through evolution, avoiding crunch.
Can avoid singularity in black hole interiors??? - Kantwoski-Sachs spacetime approach to Schwarzschild
Detecting of Falsifying the Multiverse: David Spergel (Princeton)
Premise: multiverse would likley lead to mixed initial state not pure state ( - so not a Bunch-Davies vacuum - see above).
Possible multiverse signature - oscillations in amplitude of power spectrum driven by mixing, not internal physical evolution of pure state - fiendishly clever - may lead to detectable CMB signal etc.
Meerburg et al:
Searching for Oscillations in the Primordial Power Spectrum: Perturbative Approach (Paper I)
P. Daniel Meerburg (Princeton), David N. Spergel (Princeton), Benjamin D. Wandelt (IAP) Phys. Rev. D 89, 063536 (2014) (arXiv)
Searching for Oscillations in the Primordial Power Spectrum: Constraints from Planck (Paper II)
P. Daniel Meerburg, David N. Spergel (Princeton) Phys. Rev. D 89, 063537 (2014) (arXiv)
Searching for oscillations in the primordial power spectrum
P. Daniel Meerburg (Princeton), David N. Spergel (Princeton), Benjamin D. Wandelt (IAP) Conf Proc 2014 (arXiv)

Interesting low angular mode structure known in CMD power spectrum.
Searching for oscillations in current data.
Computationally hard. Using multinest. Useful for other stuff.
Ran mock data - put synthetic CMB with oscillation into sim and recovered oscillation
Did not see clear signature of oscillations in WMAP9 data given assumptions about how modes might mix. ie they do see oscillations, but the oscillations that they see are consistent with random noise faking you out.
Thinking about other ways modes could mix - eg scalar/tensor, issues of foreground etc.

Power at large angular scales little on low side, low statistical significance.
Physics or bad luck?

Wanna use kinematic Sunyaev-Zeldovich effect to probe. Ah, my favourite!
Co-add and cross-correlate, no way to get individual signature. Use BoSS. Might work.

----Lunch break with some very diverse and interesting discussion----
A holographic theory for the very early universe: Kostas Skenderis (Southampton)
Kostas back with a talk on his own project - looking at non-geometric very early states for (holographic) universe models. I infer.
Perturbative quantum field theory in FRW spacetime breaks down, necessarily, at early times.
Possible to do falsifiable pre-big bang non-geometric theories?
Maybe in holographic framework.
Symmetries to constrain theories, and constraints from data.
----Now the complexity talks----
Emergent Complexity in the Universe: Marcelo Gleiser (Dartmouth)
Information theoretic approach.
Define shannon-like measure of field configurational entropy for bound localized energy configurations (eg solitons, or gravitationally bound systems)
Define configurational entropy, defined over k space - weighted modal fraction
minimize energy and configurational entropy
solutions "bundles or irreducible complexity" - [are they? locally irreducible? globally?]
Questions at that point - short answer: no formal proof, but it works!
- Configurational entropy minimized in nature
- Configurational entropy maximized at instability point of bound state - interesting
- Configurational entropy can be used to detect complext structures
No action principle for configurational entropy, yet.
Very useful if true. Needs some work, potentially very useful.

Other interesting possibilities: configurational entropy as signature of phase transition critical points (first order?) and coupling to external environment issues.
Cognitive Astrophysics: Barry Madore (Carnegie)
Series of 4 Carnegie-Templeton workshops on Emergence and Complexity etc.
Roundtable closed sessions between astrophysicists and philosophers.
Tutorials followed by Appreciations.
Interesting list of topics and participants... apparently nothing about them online, unfortunately.

Question: are semi-analytic models science? ;-)
Initial Information Folding and Flowing into Complexity: Mark Neyrinck (JHU)
Dark matter fluctuations as source of information.
"Loss of information" (classical) into entropy.
Are there substantial non-primordial information sources?
Structure formation analogous to folding of CDM phase space
Ringing the initial Universe: the response of overdensity and transformed-density power spectra to initial spikes, Mark C. Neyrinck, Lin Forrest Yang (JHU), MNRAS (August 01, 2013) 433 (2): 1628-1633 (arXiv)

Or, Fold your own galaxies HT @shaka_lulu
The emergence of complex structural patterns: Sergei Shandarin(Kansas)
More phase space folding of dark matter and caustics on submanifolds
We are unable to define complexity consistently - that may not be critical - one these things where diversity may be a virtue.

Bousso proposes that rate of entropy generation is what matters, not absolute amount.
Hmm.
Testing the Multiverse: Anthony Aguirre (UCSC)
Inflation - one shot or eternal - testable?
Nice graphics... I still want some of those for my class!
For (some) inflation potential, phase transitions can't "catch up" with rest of space still inflating - hence inflation is unbounded, can be very large, possibly infinite.
That's when it gets interesting.
NB: each bubble of space-time in the bigger multiverse can itself be infinite. Cute.

Bubbles can collide - ie universe-universe collisions within the multiverse.
This is where potentially testable predictions come in.

Simulating the universe(s): from cosmic bubble collisions to cosmological observables with numerical relativity

Carroll L. Wainwright, Matthew C. Johnson, Hiranya V. Peiris, Anthony Aguirre, Luis Lehner, Steven L. Liebling
JCAP03(2014)030 (arXiv)

"Scientists look for other Universes, find 4"...

catdynamics Tue, 06/17/2014 - 03:49

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Searching for Kardashev Type II and III Civilizations with WISE - the Video

catdynamics — Wed, 18 Sep 2013 14:03:30 +0000

Searching for Kardashev Type II and III Civilizations with WISE - the Video

The google+ hangout on SETI searches for KII and KIII aliens using WISE is archived on Youtube:

Enjoy

catdynamics Wed, 09/18/2013 - 10:03

Tags

Searching for Kardashev Type II and III Civilizations with WISE

catdynamics — Tue, 17 Sep 2013 23:09:55 +0000

Searching for Kardashev Type II and III Civilizations with WISE

A google hangout this afternoon:

"Today, September 18, 2:00 PM

SETI Institute researchers Jill Tarter and Franck Marchis (host & moderator) will hangout with Jason Wright, professor of astronomy at Penn State, Matt Povich, professor of astronomy at Cal Poly Pomona and Freeman Dyson, theoretical physicist and mathematician at the Institute for Advance Study.

These scientists will discuss the potential for the WISE telescope to detect extraterrestrial super-civilizations that acquired a large energy supply by building a mega-structure to harvest the energy of their star("Dyson Sphere") or their entire galaxy."

#SETIChat #SETIHangout

This is a discussion of the active research project currently under way, lead by Prof. Wright that I have previously alluded to

Jason has done a series of blog posts on the issue, some of which I have linked to before, and some more of which are below:

Big Spheres Around Small Stars - Dyson spheres around the lowest mass M stats are special

Artifact SETI

Waste Heat, part VI: A "physicist's definition" of intelligence

Waste Heat part VII: SETI beyond the Milky Way

There is a good writeup of the general issue "Distant ruins" in Aeon magazine.

catdynamics Tue, 09/17/2013 - 19:09

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exoplanetology sundries

catdynamics — Mon, 11 Mar 2013 22:54:13 +0000

exoplanetology sundries

There were a number of interesting results reported today, the start of what promises to be an interesting week:

IR spectra of HR 8799 planets - Scharf at SciAm blogs reports on the Oppenheimer et al paper using the P1640 at the Palomar telescope.

Their interpretation of the rather low signal-to-noise low resolution spectra is that the outer two planets have little methane in their upper atmosphere and the inner planets do seem to have methane and that there is evidence for ammonia in the outer planets.

I suspect more data is needed.

HR8799 is an interesting system, I'm still not convinced by the standard model, but my alternative conjecture may be too alternative....
Maybe I ought to just write it up.

Charles Cockerell goes all negative on alien life - I'm getting a strange negative vibe from the SETI community, not sure what is driving it, my personal sense is the opposite that prospects for life are massively improving as we learn more.

Kepler Mission Manager Update: urgh.
After the deliberate entry into safe mode of the spacecraft earlier this year, the preliminary read is that reaction wheel #4 is still acting up - exhibiting symptoms consistent with the failure mode of the previous reaction wheel.
Kepler only has 4 reaction wheels.
One is broken.
It needs 3 to operate.

The housekeeping data was downloaded last week, and ought to give a more robust diagnosis of what is going on once it has been analysed.

We really need Kepler to survive the extended mission and not flake out just as things are about to get really interesting.

New blog - High Metallicity

catdynamics Mon, 03/11/2013 - 18:54

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Just a note. blog URL/name have changed.

Thanks for the free publicity :P

Free?!
"There ain't no such thing as Free Publicity!"

id these sf stories...

catdynamics — Wed, 06 Feb 2013 00:44:27 +0000

id these sf stories...

Ok - I'm crowdsourcing the internet, because the google has failed:

there are two science fiction short stories that I need titles and authors for, source in anthology or collection would be better still.

1) humans in slower-than-light spaceship set out to colonize planet identified around nearby star. When they finally get there, they find the planet already colonized by humans, who had left after them but on a faster (ftl?) spaceship and arrived before them

2) humans expand around galaxy and find no intelligent life - finally contact is made, arrangements are set up to treat with aliens, and it is quickly realized that the aliens are the other edge of the human expansion through the galaxy, coming around from the other side, with some genetic and morphological drift

Yes, I need this for Actual Real Science, not just my own amusement

catdynamics Tue, 02/05/2013 - 19:44

Tags

Science

Kardashev

SETI

The first one sounds like the premise of Robert Sheckley's "The Native Problem" (1956, Notions: Unlimited). I'm not sure if its the one you are looking for, since like most of Sheckley's work its more of a comedy/satire with a SF backdrop than 'pure' SF. The world is also not strictly colonized, since the FTL humans consisted of only one individual, who the later arriving humans believe to be a native of the planet, despite any claims to the contrary. Nevertheless, I highly recommend all of Sheckley's work, as he is still my favorite SF author with some of the best satire ever written (imho). For the second story I don't have a clue.

Could the first one be "Time for the Stars" by Robert Heinlein? Can't remember exactly but this seems like the premise of the story or similar. Good luck on your search/research!

#1 sounds a bit like the origin story of vance astro, from marvel comics. though the rest of your synopsis suggests you're thinking of something else...

1) Far Centaurus by A.E van Vogt. Collected in http://en.wikipedia.org/wiki/Destination:_Universe!

2) Final Encounter by Harry Harrison. Collected in
http://en.wikipedia.org/wiki/Two_Tales_and_Eight_Tomorrows

My strategy was to use the tvtrope people to do the hard work:
http://tvtropes.org/pmwiki/pmwiki.php/Main/LightspeedLeapfrog
http://tvtropes.org/pmwiki/pmwiki.php/Main/HumanSubspecies

I recognize the first, but can't call up the title and author right now. I'll give it further thought. I should warn you, though, that the situation you described has been used more than once.

The second was unfamiliar to me.

I've passed on your query to an SF editorial colleague who is good at answering these questions.

Also, if you haven't already, you should look here:

http://www.sf-encyclopedia.com/

OK, I think the first one might be "Far Centaurus" by Van Vogt.

Here's a description from Wikipedia:

"Far Centaurus (1944), short story by A. E. van Vogt published in the collection Destination: Universe! (1952). A crew of Terran explorers who have been hibernating through a centuries-long voyage to Alpha Centauri discover on arrival that their technology has been radically superseded; humanity has arrived at the Alphan planet Pelham via superluminal travel long before them, and has long forgotten about them and their primitive mission (compare Comics: Guardians of the Galaxy below). The travelers must overcome their childlike naïveté to cope with the near Godlike human civilization that has evolved in their absence—a good example of the "quasimessianic ... transcendental omnipotence" with which van Vogt often furnishes his protagonists in order to generate a sense of wonder in his tales.[6]"

For the first, what leaped to my mind is "Far Centaurus," a short story by A. E. van Vogt published in the collection Destination: Universe! (1952).

The second sounds vaguely familiar but I can't hazard a guess.

#1 could be from all sorts of stories, but the likeliest is Heinlein's story of telepathic twins, one of whom stays back on Earth while the other rides off to other planets: Time for the Stars.

Not sure about #2 yet.

I can tell you they are both ideas I have toyed with in the past. The first was even outlined and partially drafted!

The second sounds like Harry Harrison's "Final Encounter". TVTropes summarises it as:

Harry Harrison's short story "Final Encounter" had a team with members of two Human Subspecies looking for nonhuman intelligence. At the end, the very promising new species, which can't even breathe the same air we do, turns out to be of Earth descent too — one group was expanding and searching clockwise around the galaxy, the other counter-clockwise.
"We are alone," Hautamaki said, looking at the massed trillions of stars. "We have closed the circle and found only ourselves. The galaxy is ours, but we are alone."

If you can't find the first, you could try posting a YASID request (Yet Another Story ID) to rec.arts.sf.written, which generally gets a series of rapid and knowledgeable replies.

I remember something like 2) - a minor plot point was that the supposed aliens had a writing system unrelated to anything known in supposedly human history, which was an argument for their actual being alien, before the biochemical analysis came in.

I'm pretty sure I read this in Asimov's SF (in German translation) sometime back in the 90s... maybe something by Poul Anderson?

Also, they have a whole page on the first plot. A bit worrying that I ended up there for both. I'd have thought the SF Encyclopedia would have been the best source.

Thanks all: Far Centaurus and Final Encounter are indeed the ones I was looking for.
The Internet again proves its wisdom again.
tvtropes sounds like an interesting resource, didn't know of it.
Was just thinking that it would have been a perfect rasfw query, didn't realise Usenet rumps still live out there.

I see that others have beat me to the answers.
Here are the collections they were published in:

Far Centaurus
http://www.isfdb.org/cgi-bin/title.cgi?41417

Final Encounter
http://www.isfdb.org/cgi-bin/title.cgi?59032

Hmph. The first storyline is exactly parallel to a short story I wrote in junior high in the early 70s. It won a grade-level English prize in my school and was 'published' in the school's literary magazine - a copy is still wedged in somewhere in my Dad's bookcase. Now I realize it must have been planted in my brain from an earlier story I had read. Please dont' tell...