PRL, Amdavad, january 7, 2015PRL, Amdavad, january 7, 2015

Galactic Neutrino Galactic Neutrino Communication & SETICommunication & SETI

Sandip PakvasaSandip Pakvasa

University of HawaiiUniversity of Hawaii

(SETI=Search for Extra-Terrestrial Intelligence)

““Work” in collaboration with:Work” in collaboration with:

Walt Simmons, Xerxes Tata, John Learned, Tony Zee, Rolf-Peter Kudritzki

This work is NOT supported by: DOE, NSF,NASA, DOD, DARPA…….…..Not even by the SETI Institute!

Neutrino Communication is a very Neutrino Communication is a very old idea:old idea:

H. Saenz et al., 1977H. Saenz et al., 1977 J. Albers, P. Kotzer & D.Padgett, 1978J. Albers, P. Kotzer & D.Padgett, 1978 M. Subotowicz, 1979M. Subotowicz, 1979 J. Pasachoff & M. Kutner, 1979J. Pasachoff & M. Kutner, 1979 They had the basic idea to use neutrino beams forThey had the basic idea to use neutrino beams forinterstellar and terrestrial communication based interstellar and terrestrial communication based on the penetrating power of neutrinos……….on the penetrating power of neutrinos……….Also proposed use for communicating with submarines, getting the Also proposed use for communicating with submarines, getting the

US Navy interested! (Needless to say, one way only!)US Navy interested! (Needless to say, one way only!)A recent proposal is to use neutrino beams from muonA recent proposal is to use neutrino beams from muoncolliders: Z. Silagadze, arXiv:0803.0409(2008). colliders: Z. Silagadze, arXiv:0803.0409(2008). Idea of neutrino communication with submarines has been Idea of neutrino communication with submarines has been revived very recently: P. Huber, arXiv:0909.4554(2009),Phys. Lett. revived very recently: P. Huber, arXiv:0909.4554(2009),Phys. Lett.

B692,268(2010).B692,268(2010).In early ´70´s neutrino beams of high energies around 50-100 GeVIn early ´70´s neutrino beams of high energies around 50-100 GeVBecame available at the new machine at FermiLab.... and later at Became available at the new machine at FermiLab.... and later at

CERN.CERN.And neutrino cross-sections rise with energy!And neutrino cross-sections rise with energy!

SETI: Search for Extra-SETI: Search for Extra-terrestrial Intelligenceterrestrial Intelligence

There should/might be many advanced There should/might be many advanced civilizations(ETI) out there in the galaxy……civilizations(ETI) out there in the galaxy……

Fermi’s question(1950), sometimes called Fermi’s question(1950), sometimes called Fermi’s paradox: where are they (the Fermi’s paradox: where are they (the signals)? Namely, if they are out there why signals)? Namely, if they are out there why havent we seen or heard from them?havent we seen or heard from them?

Maybe security concerns prevent them Maybe security concerns prevent them from revealing themselves?from revealing themselves?

Maybe they would like to send info on a Maybe they would like to send info on a variety of topics…..?variety of topics…..?

Too Many Possible Scenarios, no point in Too Many Possible Scenarios, no point in trying to guess, just look for signals…trying to guess, just look for signals…

New Fact:

SETI has become somewhat more urgent since the recent discovery that the number of habitable planets within the Milky Way may be in the billions(one out of five stars like the sun has them!)

That does not necessarily mean that any of them has advanced civilizations (let alone life) but certainly raises the odds….

History/origin of “The Fermi History/origin of “The Fermi question”question”

1950: Herb York, Edward Teller, Emil 1950: Herb York, Edward Teller, Emil Konopinski and Fermi were meeting for Konopinski and Fermi were meeting for lunch at Los Alamos. Fermi was running lunch at Los Alamos. Fermi was running late...Before Fermi arrived, the talk was late...Before Fermi arrived, the talk was about a recent cartoon in the New about a recent cartoon in the New Yorker magazine about two recent Yorker magazine about two recent headline stories making news-reports, headline stories making news-reports, one on flying saucers and the other on one on flying saucers and the other on disappearing trash cans in NYC! disappearing trash cans in NYC!

New Yorker 1950New Yorker 1950

On arrival, Fermi’s reaction (as a world On arrival, Fermi’s reaction (as a world class phenomenologist) was that the class phenomenologist) was that the “model” in the cartoon was obviously “model” in the cartoon was obviously correct as it explained TWO unrelated correct as it explained TWO unrelated events!events!

Later on during the lunch, out of the Later on during the lunch, out of the blue, in the middle of a conversation blue, in the middle of a conversation about something else altogether, Fermi about something else altogether, Fermi is reported to have exclaimed “Where is reported to have exclaimed “Where are they?”are they?”

It was clear to the others what he had It was clear to the others what he had meant……..meant……..

J.J. Gomez-Cardenas...fictionalised accountJ.J. Gomez-Cardenas...fictionalised account

of of thisthis lunch.... lunch....

One may argue that the question raised by Fermi was a bit premature as

any systematic searches for ETI were not even

started at that time! Even ideas about how to

perform such searches came later!That would not happen

for another 10 years, till 1960!

Fermi’s Question has given rise Fermi’s Question has given rise to much discussion and attempts to much discussion and attempts to answer it…..including books..to answer it…..including books..

One implication was that since we have not One implication was that since we have not seen/heard from them, there are no ETI: there is seen/heard from them, there are no ETI: there is no one out there. no one out there.

One simple response is: Absence of evidence is One simple response is: Absence of evidence is NOT evidence of absence!NOT evidence of absence!

An even simpler and telling one is due to Calvin An even simpler and telling one is due to Calvin and Hobbes: The fact that no one has tried to and Hobbes: The fact that no one has tried to contact us IS Itself Proof of Extra terrestrial contact us IS Itself Proof of Extra terrestrial Intelligence!!(November 12, 2008).Intelligence!!(November 12, 2008).

Judging by our activities, they(ETI) may think WE Judging by our activities, they(ETI) may think WE are not intelligent/important enuf.. And not worth are not intelligent/important enuf.. And not worth the effort!the effort!

Calvin vs Fermi!Calvin vs Fermi!

Fermi’s Question has given rise to much Fermi’s Question has given rise to much discussion and attempts to answer it… discussion and attempts to answer it…

including books..including books.. One implication was that One implication was that

since we have not since we have not seen/heard from them, seen/heard from them, there are no ETI: there are no ETI: there is there is no one out there. no one out there.

One simple response is: One simple response is: Absence of evidence is Absence of evidence is NOT evidence of absenceNOT evidence of absence!!

An even simpler and An even simpler and telling one is due to Calvin telling one is due to Calvin and Hobbes: The fact that and Hobbes: The fact that no one has tried to contact no one has tried to contact us IS Itself Proof of Extra us IS Itself Proof of Extra terrestrial Intelligence!! terrestrial Intelligence!! (November 12, 2008).(November 12, 2008).

Comment in Comment in the Walt Kelly the Walt Kelly

Strip “Pogo Strip “Pogo Possum” by Possum” by Porky Pine:Porky Pine:

““There’s only two possibilities. There There’s only two possibilities. There is life out there in the Universe that’s is life out there in the Universe that’s smarter than us, or else we’re the smarter than us, or else we’re the most intelligent life in the Universe. most intelligent life in the Universe. Either way, it’s a mighty sobering Either way, it’s a mighty sobering thought.”(maybe even scary)thought.”(maybe even scary)

These authors consider a number of scenarios ranging from optimistic to most pessimistic.

1. BENEFICIAL: 1. Mere detection 2. Cooperative/Helpful E.T.s help with science, and avoiding global catastrophes and other problems. 3. Uncooperative E.T.s 2. NEUTRAL: 1. Invisible/hiding intentionally 2. Not interested 3. Noticeable but indifferent 4. Mildly curious and/or nuisance

value 3. HARMFUL: 1. Selfish ETI (destroy or enslave or

attack us) 2. Unintentional harm 3. Information Hazard (computer

virus, bio-hazard, general demoralizing impact)

Until about 1960, SETI remained in the Science Fiction domain. Only in 1959-61 did it become

“Science!”Of course, that has

never stopped people from speculating, then

as well as now!

Suggestion to use 21 cm line as a carrier Suggestion to use 21 cm line as a carrier for a possible ETI signal due to Cocconi for a possible ETI signal due to Cocconi and Morrison in 1959.and Morrison in 1959.

Recall the 21 cm line is due to Recall the 21 cm line is due to interstellar hydrogen de-excitation by interstellar hydrogen de-excitation by hyperfine structure.hyperfine structure.

Half-life 11 million years.Half-life 11 million years. First search started by Drake et al in First search started by Drake et al in

1960-1, with the Ozma Project and Drake 1960-1, with the Ozma Project and Drake Equation in 1961Equation in 1961

But Photons can be obscured/attenuated But Photons can be obscured/attenuated as opposed to neutrinos; also scattered as opposed to neutrinos; also scattered leading to jitter in time & direction.leading to jitter in time & direction.

Less background and noise for a Neutrino Less background and noise for a Neutrino signal………..signal………..

Drake Equation is an attempt to estimate the chances of detecting a signal at earth from ETI

N =Rs .fp.ne.fl.fi.fc.L

N = the number of civilizations in our galaxy with whom we can communicate

Rs = average rate of star formation in the galaxyfp = fraction of stars with planets

ne = average number of planets with potential for life

fl = fraction to develop life at some pointfi = fraction that develop Intelligent life

f

Fc = fraction to develop technology that releases signs into space

L = length in time over which they will release such signs

Unfortunately, we don’t really know any of thse numbers, so it remains purely guesswork.

Estimates vary wildly. The original estimates at the first SETI

meeting in 1960 were 36 million to one billion.

Current estimates are from a low of 2 to a high of 3 billion!

Critics point out that these are not meaningful and the number can be anywhere from “zero to billions and billions!”

New Initiatives(2014):New Initiatives(2014): Just like we are doing, ETI may be Just like we are doing, ETI may be

sending out ¨leaked¨signals sending out ¨leaked¨signals inadvertently.....inadvertently.....

To search for such a new program will To search for such a new program will sample some 30 stars(including sample some 30 stars(including binaries) within 5 parsecs of the sun and binaries) within 5 parsecs of the sun and look for signals at many frequencies at look for signals at many frequencies at many telesopes.....at short distances, many telesopes.....at short distances, the demand on technogy are quite the demand on technogy are quite modest...modest...

A second idea is to try to eavesdrop on A second idea is to try to eavesdrop on signals broadcast from one planet to signals broadcast from one planet to another in multi planet systems.......another in multi planet systems.......

A new class of objects has been discovered very recently:”fast radio

bursts”They are quite mysterious and are

characterised by very high flux densities, high rates, perhaps

coherence at the source….big debate on the nature of the sources

There has been a suggestion that these are signals beamed at us from ETIS?

J. Luan and P. Goldreich, arXiv:1401.1795

Neutrinos & SETI: Obviously a Neutrinos & SETI: Obviously a very hot topic judging by very hot topic judging by

citations:citations: Walt Simmons, John Learned, Xerxes Tata, Walt Simmons, John Learned, Xerxes Tata,

SP, Q. J. Roy. Astro. Soc. (1994).SP, Q. J. Roy. Astro. Soc. (1994).

#Cit.= 2#Cit.= 2 John Learned, Tony Zee, SP, Phys. Lett. John Learned, Tony Zee, SP, Phys. Lett.

B(2009).B(2009).

#Cit. = 4#Cit. = 4 John Learned, Tony Zee, Rolf-Peter Kudritzki, John Learned, Tony Zee, Rolf-Peter Kudritzki,

SP, Contemparory Physics(2012).SP, Contemparory Physics(2012).

#Cit. = 0#Cit. = 0

(excluding self-citations)(excluding self-citations)

Although many in non-technical magazine Although many in non-technical magazine ( e.g. The Economist) and in many blogs ( e.g. The Economist) and in many blogs etc….etc….

Demonstration of Communication using neutrinos: D. Stancil et al., arXiv:1203.2847(2012)

Abstract: Beams of neutrinos have been proposed as a

vehicle for communications under unusual circumstances, such as direct point-to-point global communication, communication with submarines, secure communications and interstellar communication. We report on the performance of a low-rate communications link established using the NuMI beam line and the MINERvA detector at Fermilab. The link achieved a decoded data rate of 0.1 bits/sec with a bit error rate of 1% over a distance of 1.035 km, including 240 m of earth.

(essentially beam off beam on, with a pulse timing separation of about a microsecond)

Three Possible ScenariosThree Possible Scenariosto be discussed (in order of to be discussed (in order of

more to less more to less conservative=plausibility):conservative=plausibility):

Timing Data Communication with Timing Data Communication with neutrinosneutrinos

Sending a focused beam of Sending a focused beam of neutrinos ofneutrinos of

a definite energya definite energyDisturbing a Cepheid variable star Disturbing a Cepheid variable star

with a neutrino beam to modulate with a neutrino beam to modulate its periodits period

Other possibilities include using Other possibilities include using expansion of the universe.... expansion of the universe....

Timing Data Communications Timing Data Communications & SETI (1994)& SETI (1994)

Currently our time standards based on Cs Currently our time standards based on Cs Fountain Clocks(now overtaken by Fountain Clocks(now overtaken by Ytterbium clocks), accuracy 1 part in 10Ytterbium clocks), accuracy 1 part in 101717, , Josephson junctions can potentially go to Josephson junctions can potentially go to 10101919..

Due to chaos and GR corrections, need Due to chaos and GR corrections, need synchronization signals to keep accurate synchronization signals to keep accurate time, not necessarily frequent, e.g. VLBI time, not necessarily frequent, e.g. VLBI will need accurate timing data over huge will need accurate timing data over huge distances. Local clocks need to exchange distances. Local clocks need to exchange timing data to remain synchronized.timing data to remain synchronized.

Hence need stable clocks of highest Hence need stable clocks of highest precision->fast processes for transmitting precision->fast processes for transmitting

and receiving markers & form of radiation and receiving markers & form of radiation to convey faithfully data over enormous to convey faithfully data over enormous distances.distances.

A very advanced ETI would presumably A very advanced ETI would presumably need ever more accurate timing need ever more accurate timing eventually physics limit timing.eventually physics limit timing.

Shortest time interval known today is the Shortest time interval known today is the Z lifetime about 10Z lifetime about 10-25-25 sec. sec.

This suggests use of neutrinos from the decay of Z as an ideal carrier. (open problem: how to make Z-clocks!) We imagine that an ETI is doing just that at distancesof order of kiloparsecs in the galaxy for its own spreadout outposts…We expect to see neutrinos of energy of about 45.5 GeV.To get a few events per year in a KM3 detector, weestimate power requirement at the source to be enormous: about solar luminosity!Such an ETI source would look like a “Dyson shell”!Who knows, after all there are over 50,000 IR sourcesIdentified by IRAS……..In any case this is not OUR problem. (this will be my Mantra). All we need to do is wait and look for the neutrino signal at half the Z mass, clean with no backgrounds. ICECUBE is waiting….Simmons,Learned,Pakvasa & Tata, Q.J.R.Astr.Soc. 35,321(1994)

““Dyson Shell”Dyson Shell” Dyson shell(or Sphere) is a name for stars which Dyson shell(or Sphere) is a name for stars which

areare being harnessed by advanced civilizationsbeing harnessed by advanced civilizations and have energy being expended to sustainand have energy being expended to sustain them, using up most of the radiation energythem, using up most of the radiation energy by having a bunch of absorbers around the starby having a bunch of absorbers around the star(Also possible, is mining a macroscopic black hole (Also possible, is mining a macroscopic black hole

formed from a star with buckets going around a la formed from a star with buckets going around a la the example in Misner, Thorne and Wheeler.)the example in Misner, Thorne and Wheeler.)

Dyson first proposed such structures for use by Dyson first proposed such structures for use by advanced civilizations which have reached a stage advanced civilizations which have reached a stage of requiring huge energy consumption and of requiring huge energy consumption and discussed them(1960) and pointed out discussed them(1960) and pointed out

that they would be sources of intense infra-red that they would be sources of intense infra-red radiation due to the thermal energy output. radiation due to the thermal energy output.

From Misner, Thorne and Wheeler

Misner,Thorne, andWheeler

Focused/Directed beam of Focused/Directed beam of neutrinosneutrinos

Why would ETI want to send us a Why would ETI want to send us a focused beam?focused beam?

Don’t know and don’t care! Maybe they Don’t know and don’t care! Maybe they want to get our attention and then send want to get our attention and then send us information (e.g. “Beware string us information (e.g. “Beware string theory!” ) Due to long time scales, theory!” ) Due to long time scales, may remain monologue for a while.may remain monologue for a while.

Many different possibilities: intercept Many different possibilities: intercept signals sent by ETI to their “military” signals sent by ETI to their “military” outposts, we just happen to intercept outposts, we just happen to intercept them…..them…..

Sending a focused beam has the Sending a focused beam has the advantage of not being seen by all, advantage of not being seen by all, and would be less “dangerous”, and would be less “dangerous”, perhaps an advanced ETI wants to perhaps an advanced ETI wants to transmit to a TEStransmit to a TES

( Technologically Emergent Society) ( Technologically Emergent Society) like ourselves.like ourselves.

Perhaps they have been tracking us and Perhaps they have been tracking us and know that we as a TES are ready to know that we as a TES are ready to receive neutrino signals with large KM3 receive neutrino signals with large KM3 detectors?detectors?

Beam choice: electron antineutrinos of Beam choice: electron antineutrinos of energy 6.3 PeV. The cross-section on energy 6.3 PeV. The cross-section on electrons in detectors is large and electrons in detectors is large and characteristic of the Glashow Resonance characteristic of the Glashow Resonance (produce on-shell W with a resultant (produce on-shell W with a resultant shower). No BG and a unique shower). No BG and a unique characteristic energy. characteristic energy.

Range in Water at this energy ~ 100 km Range in Water at this energy ~ 100 km planned detectors will catch ~ 1 % of the planned detectors will catch ~ 1 % of the flux (down-going and horizontal). flux (down-going and horizontal).

Glashow ResonanceGlashow Resonance

When a anti-When a anti-ννe e hits an electron in the hits an electron in the target at an energy of 6.3 PeV(10target at an energy of 6.3 PeV(106 6

GeV),GeV),

the total energy in c.m. is just enuf to the total energy in c.m. is just enuf to

produce a Wproduce a W- - . At this resonant energy . At this resonant energy the cross-section is high and the the cross-section is high and the signal due to the shower of the decay signal due to the shower of the decay of the W is clear………..of the W is clear………..

Such a resonance was first discussed by Glashow in 1960. Such a resonance was first discussed by Glashow in 1960. Shower events in the PeV energy Range have been seen by Shower events in the PeV energy Range have been seen by Icecube….(2012) Icecube….(2012)

--

A possible way to make such A possible way to make such neutrinos is an eneutrinos is an e++-e-e- - Collider in a Collider in a boosted frame with eboosted frame with e- - overtaking the overtaking the ee++, making Z’s of high energy….., making Z’s of high energy…..

From 1 kpc away this beam would be From 1 kpc away this beam would be 3000 AU across, for a pulse of 100 3000 AU across, for a pulse of 100 neutrinos, need 10neutrinos, need 1026 26 neutrinos in the neutrinos in the beam! Again NOT OUR PROBLEM!beam! Again NOT OUR PROBLEM!

A much better choice is a pion A much better choice is a pion accelerator….see e.g. next slide.accelerator….see e.g. next slide.

Learned, Pakvasa & Zee, Phys. Lett. B 671, 15(2009),arXiv:0805.2429.

Artist’s conception

Basic idea similar to producing a muon beam…..

Protons hitting a target at ~30 PeV, Protons hitting a target at ~30 PeV, switchable between πswitchable between π++ and π-, decaying into μ and π-, decaying into μ and νand νμ μ or their antiparticles. Muons are or their antiparticles. Muons are removed as in usual beam dumps…A pure νremoved as in usual beam dumps…A pure νμ μ

beam, after a few light-days becomes a flavor beam, after a few light-days becomes a flavor mixture with νmixture with νee:ν:νµµ:ν:ντ τ = 4:7:7.= 4:7:7.

Encoding in a variety of ways: switching back Encoding in a variety of ways: switching back and forth between neutrinos and and forth between neutrinos and antineutrinos, i.e. absence or presence of the antineutrinos, i.e. absence or presence of the Glashow Resonance, in addition to other Glashow Resonance, in addition to other signals(muons etc). One can also use signals(muons etc). One can also use timing/pulsing.timing/pulsing.

Neutrino angle small ~ from 3 kpc, about Neutrino angle small ~ from 3 kpc, about 0.01 AU, much narrower than from Z decay.0.01 AU, much narrower than from Z decay.AGAIN ALL WE HAVE TO DO IS SIT BACK AND AGAIN ALL WE HAVE TO DO IS SIT BACK AND

WAIT WAIT FOR SIGNAL OF 6.3 PEV ELECTRON FOR SIGNAL OF 6.3 PEV ELECTRON

ANTINEUTRINOSANTINEUTRINOSIN KM3 DETECTORS………..IN KM3 DETECTORS………..

Since decays of pions produce only Since decays of pions produce only ννμμ’s, we rely ’s, we rely on neutrino oscillations to convert them into on neutrino oscillations to convert them into mixtures including mixtures including ννee’s. At large distances, ’s. At large distances, oscillations average out and the only effect is oscillations average out and the only effect is mixing. The propagation matrix is such that an mixing. The propagation matrix is such that an initiallyinitially

pure pure ννμμ beam becomes a mixture beam becomes a mixture

given by given by ννee::ννµµ::ννττ = 4:7:7 = 4:7:7

Also a beam of Also a beam of ννµ µ produces NO antineutrinos produces NO antineutrinos needed for the Glashow resonance. (needed for the Glashow resonance. (ππ++->->ννμμ , , ππ-- -> ->ννµµ _bar ) so need to be able to accelerate _bar ) so need to be able to accelerate both charges and switch back and forth both charges and switch back and forth between them......between them......

Neutrinos mix and oscillate.Neutrinos mix and oscillate.

Some encouraging news!

Finally we have seen some very high energy

(100 TeV to 2 PeV) neutrino events in the Icecube detector which seem to be

Extra-terrestrial……

“Evidence for High Energy Extraterrestrial Neutrinos in the Icecube Detector”, M. G. Aartsen et al., Science, 342, 124856(2013); also arXiv:1311.7048.

But no Glashow resonance events yet…..

Maybe soon?

A Message from the A Message from the Cepheids?Cepheids?

Henrietta Leavitt’s discovery of the Henrietta Leavitt’s discovery of the luminosity-period relation allowed luminosity-period relation allowed Hubble to make his discovery & made Hubble to make his discovery & made cosmology possible (see recent cosmology possible (see recent biography “Miss Leavitt’s Stars”)biography “Miss Leavitt’s Stars”)

Learned, Kudritzki, Pakvasa, & Zee

arXiv/0809/0809.0339

submitted to and rejected by Phys Rev.. Lett.

Accepted and published by Contemparory Phyics

1908:

•A Cepheid variable is a member of a particular class of variable stars, notable for tight correlation between their period of variability and absolute luminosity.

• Namesake and prototype of these variables is the star Delta Cephei, discovered to be variable by John Goodricke in 1784.

• This correlation was discovered and stated by Henrietta Swan Leavitt in 1908 and given precise mathematical form by her in 1912.

• Period-luminosity relation can be calibrated with great precision using the nearest Cepheid stars.

• Distances found with this method are among the most accurate available.

- Leavitt, rietta S. "1777 Variables in the Magellanic Clouds". of Harvard College Observatory. LX(IV) (1908) 87-110. - P C. "Periods of 25 Variable Stars in the SMC". Harvard Collegey Circular 173 (1912) 1-3.

The Cepheid variables proved The Cepheid variables proved extremely useful:extremely useful:

In 1915 they were used by Harlow In 1915 they were used by Harlow Shapley to measure the size & Shapley to measure the size & shape of the milky way, and the shape of the milky way, and the location of the sun in it.location of the sun in it.

In 1924, Edwin Hubble used them to In 1924, Edwin Hubble used them to measure distance to the measure distance to the Andromeda galaxy and proved that Andromeda galaxy and proved that it is not part of the milky way! (End it is not part of the milky way! (End of the Island Universe idea!)of the Island Universe idea!)

In 1929, Humason and Hubble In 1929, Humason and Hubble

showed that the universe is showed that the universe is expanding!expanding!

In mid –’40s, Baade showed that In mid –’40s, Baade showed that

there are two different classes of there are two different classes of Cepheid variables with differing Cepheid variables with differing velocity-luminosity relationship velocity-luminosity relationship and thus revised and thus revised

the distance scale by about a factor the distance scale by about a factor of 2……(classical and type II).of 2……(classical and type II).

Measure period and apparent magnitude (brightness),

Period -> Absolute magnitude

Distance = RefDist x sqrt(Absolute/Apparent)

Cepheid MechanismCepheid MechanismCepheid usually a population I giant yellow star, pulsing regularly by expanding and contracting, regular oscillation of its luminosity from 103 to 104 times L☼

Cepheids, population I stars: “Type I Cepheids”, Similar (population II) W Virginis: Type II Cepheids.

Luminosity variation due to cycle of ionization of helium in the star's atmosphere, followed by expansion and deionization. Key: ionized, the atmosphere more opaque to light.

Period equal to the star's dynamical time scale: gives information on the mean density and luminosity.

Model for Cepheid VariablityModel for Cepheid Variablity

Basic idea given by Eddington in Basic idea given by Eddington in 1917:1917:

Doubly ionized He is more Doubly ionized He is more opaque (than, say singly ionized opaque (than, say singly ionized He) At the dimmest point of the He) At the dimmest point of the cycle, the gas is most opaque, cycle, the gas is most opaque, and outermost layers heat and and outermost layers heat and expand, as the gas expands, it expand, as the gas expands, it begins to cool, so becomes less begins to cool, so becomes less ionized and hence more ionized and hence more transparent, radiation escapes. transparent, radiation escapes. The expansion stops and star The expansion stops and star contracts due to gravity. And the contracts due to gravity. And the process repeats.process repeats.

(The identification of He was due (The identification of He was due

to Zhevakin in 1953 . Extensive to Zhevakin in 1953 . Extensive detailed modeling for the P and detailed modeling for the P and time variation of P exists in the time variation of P exists in the literature.) literature.)

Cepheid Light CurvesCepheid Light Curves

Typical saw tooth pattern

Sample of data fromHubble Key project measured 800 Cepheids, out through Virgo Cluster

Period-luminosity relation

Feast & Catchpole, 1997

Recent most accurate form

There are also rr Lyrae stars which are There are also rr Lyrae stars which are variable and periodic with similar variable and periodic with similar

characteristics as Cepheids. They are smaller characteristics as Cepheids. They are smaller and less luminous , and so difficult to see at and less luminous , and so difficult to see at large distances or outside our galaxy, but large distances or outside our galaxy, but

more numerous, and found in Globular more numerous, and found in Globular clusters .clusters .

They are also candidates for being modulated They are also candidates for being modulated by ETI……….by ETI……….

Many such stars show complicated time Many such stars show complicated time variation; patterns have been analysed byvariation; patterns have been analysed by

Michael Hippke, John Learned and Tony Zee Michael Hippke, John Learned and Tony Zee for evidence of coding......(see later)for evidence of coding......(see later)

How to modulate the period How to modulate the period and create a signal ?and create a signal ?

If the period can be modulated one If the period can be modulated one can magnify the signal and send it out can magnify the signal and send it out over enormous distances---over enormous distances---intergalactic!intergalactic!

This requires depositing energy deep This requires depositing energy deep inside the star so that the cycle ends inside the star so that the cycle ends earlier and the period is shortened….earlier and the period is shortened….

This is where NThis is where Neutrinoseutrinos come in, as come in, as any other method will not reach deep any other method will not reach deep inside the star…..inside the star…..

Neutrino Beam to Tickle a Star?Neutrino Beam to Tickle a Star?

The idea is to use neutrinos to deliver The idea is to use neutrinos to deliver energy at controlled depth to star, as a energy at controlled depth to star, as a giant amplifier.giant amplifier.

Cepheids fill this need…. Bright pulsing Cepheids fill this need…. Bright pulsing stars with period of instability.stars with period of instability.

Any civilization doing astronomy would Any civilization doing astronomy would monitor Cepheids as distance markers.monitor Cepheids as distance markers.

Can be seen from distant galaxies (we Can be seen from distant galaxies (we see Cepheids in the Virgo cluster).see Cepheids in the Virgo cluster).

.. Try to avoid details (which we cannot Try to avoid details (which we cannot

know) here, consider guesstimates).know) here, consider guesstimates). Guess at energy input: take Guess at energy input: take

deposition time of roughly speed of deposition time of roughly speed of sound crossing nucleus (~0.1 s). sound crossing nucleus (~0.1 s).

Take power to be 10% of stellar core Take power to be 10% of stellar core output. output.

Need Pwr ~10Need Pwr ~10-6-6 L Lcephceph . Few day . Few day Cepheid, would need 10Cepheid, would need 102828 J! But J! But again, NOT OUR PROBLEM!again, NOT OUR PROBLEM!

Tickling a Cepheid….?Tickling a Cepheid….? Could be much less energy needed… have Could be much less energy needed… have

not done studies. Not useful for now.not done studies. Not useful for now. Not to melt, need accelerator at r>100 AU, Not to melt, need accelerator at r>100 AU,

capture radiation from area ~0.1AUcapture radiation from area ~0.1AU22

Accelerators are efficient, well known Accelerators are efficient, well known physics at lower powers, but need huge physics at lower powers, but need huge technology extrapolation.technology extrapolation.

Want neutrinos of order 1 TeV to deposit Want neutrinos of order 1 TeV to deposit energy deep inside star with exponentially energy deep inside star with exponentially increasing density (energy choice selects increasing density (energy choice selects radius of deposition).radius of deposition).

Studies needed to determine how little one Studies needed to determine how little one needs to jump start expansion. But we needs to jump start expansion. But we need not solve that problem for present need not solve that problem for present purposes, simply aver that it is solvable and purposes, simply aver that it is solvable and the ETI would do so.the ETI would do so.

Light Curve of Simulated CepheidLight Curve of Simulated Cepheid

• Ordinate is stellar magnitude relative to the mean, abscissa is time in days.

• Solid curve: unmodulated (idealized) Cepheid with 2 day period and 2 magnitude luminosity excursion, with expansion taking 0.4 days.

• Dashed curve: arbitrarily modulated light curve with triggered phase advance of 0.1 day (0.05 cycle) (Data = 1110000010100110).

• Units arbitrary but representative of real data.

•The sharpness of the transitions does not matter for the present discussions.

Fourier TransformsFourier Transforms• Ordinate is the Lomb-Scargle parameter, similar to chi squared; • Fourier spectra of simulated observations of a regular periodic Cepheid variable and one with binary phase modulation. • Abscissa is frequency, 1/days.

• More complicated structure of the modulated case is not so obviously different from a noisy spectrum: one could not immediately discern that the latter case was not ``natural’’.

Frequency 1/days

Frequency 1/days

Unmodulated

Modulated

What is an ETI Signal?What is an ETI Signal? Information theory says maximally Information theory says maximally

compact data is indistinguishable from compact data is indistinguishable from noise!noise!

Interesting question: how can one tell Interesting question: how can one tell for sure when a signal is not `random’? for sure when a signal is not `random’? Or can we tell a ETI signal from a hole in Or can we tell a ETI signal from a hole in the ground? (to quote John Ellis)the ground? (to quote John Ellis)

ETI signal should have inexplicable ETI signal should have inexplicable regularities: repeated sequences, regularities: repeated sequences, letters, frames, apparent structures…. letters, frames, apparent structures…. (Applies to all SETI).(Applies to all SETI).

Who knows how they might encode?Who knows how they might encode? Hopefully we will know it when we see it!Hopefully we will know it when we see it!

Michael Hipke et al:arXiv:1409.1265, in analysing RR Lyrae stars using photometric data from Kepler space telescope, they found two regimes of long and short pulse durations. The sequences are strongly auto-correlated with coefficients of prime numbers being higher . On further sudy they seem to be of natural origin…..Although These seem to be of natural origin, further such studies are called for….

In another sudy (arXiv:1407.3442) they found that there are a few Cepheids and RR Lyrae stars, which show secondary pulsation with the ratios of the two periods very close to sq.rt of 2….with possible fine structure. So far neither of these effects seem to be a signal by ETI, but both are very interesting and encourage one to continue such analysis on a larger scale with more data.(These studies are by: M. Hippke, J. Learned, A. Zee et al.)

OutlookOutlook Unstable stellar systems such as the Cepheids can serve as Unstable stellar systems such as the Cepheids can serve as

gigantic signal amplifiers visible across the universe.gigantic signal amplifiers visible across the universe.

Assume a sufficiently advanced civilization Assume a sufficiently advanced civilization – able to tickle stars (?)able to tickle stars (?)– find it worthwhile (???). find it worthwhile (???).

Signatures of ETI communication may be available in data Signatures of ETI communication may be available in data already recorded, and that a search of Cepheid (and perhaps already recorded, and that a search of Cepheid (and perhaps other variable star, such as Lyrae) records may reveal an entre’ other variable star, such as Lyrae) records may reveal an entre’ into the galactic ‘internet’!into the galactic ‘internet’!

Certainly a long shot, but should it be correct, the payoff would Certainly a long shot, but should it be correct, the payoff would be immeasurable for humanity.be immeasurable for humanity.

Many possibilities for ETI communication: try all practical ones. Many possibilities for ETI communication: try all practical ones.

The beauty of this suggestion: data already exists, and we The beauty of this suggestion: data already exists, and we need only look at it in a new way.need only look at it in a new way.

We are NOT proposing to attempt We are NOT proposing to attempt buildingbuilding

the neutrino beams nor try to tickle thethe neutrino beams nor try to tickle the

nearest Cepheid variable star*. nearest Cepheid variable star*.

Our proposals are much more modest.Our proposals are much more modest.

Assuming that there may be some ETIAssuming that there may be some ETI

much more advanced technologically much more advanced technologically than us, and that they may be sending than us, and that they may be sending such signals (for whatever reasons of such signals (for whatever reasons of their own), we merely propose that we their own), we merely propose that we should:should:

*Nearest Cepheid is Polestar at 143 parsecs.

Summary:Action ItemsSummary:Action Items Look for 45.6 GeV(mLook for 45.6 GeV(mZZ/2) neutrino signal /2) neutrino signal

in KM3 in KM3 Look for 6.3 PeV anti-electron-neutrinos Look for 6.3 PeV anti-electron-neutrinos

in KM3 via Glashow Resonancein KM3 via Glashow Resonance Analyze Cepheid and RR Lyrae Data to Analyze Cepheid and RR Lyrae Data to

look for modulation:look for modulation: Signals are spectacular and the searchesSignals are spectacular and the searches are practically free……are practically free…… Large scale neutrino Large scale neutrino

detectors……..”builddetectors……..”build them and they will come” ! them and they will come” !

Extra SlidesExtra Slides

More on Fermi Question:More on Fermi Question: Many books and articles on this. For Many books and articles on this. For

example: Stephen Webb, “Where is example: Stephen Webb, “Where is everybody?”, Praxis Publishing, 2002.everybody?”, Praxis Publishing, 2002.

Here are listed over 50 proposals for Here are listed over 50 proposals for “solving” the Puzzle listed along with “solving” the Puzzle listed along with counter-arguments.counter-arguments.

Classes of solutions proposed:Classes of solutions proposed:

(1) They are already here!(e.g. (1) They are already here!(e.g. Hungarians? a la Szilard) Hungarians? a la Szilard)

e.g. They are Us, we ARE the aliens!e.g. They are Us, we ARE the aliens!

(2) They exist but have not yet (2) They exist but have not yet communicated…..or don’t want to!communicated…..or don’t want to!

(3) They do not exist!?(3) They do not exist!?