The Anthropic Question

George F. R. Ellis writes in Issues in the Philosophy of Cosmology:

9.1 Issue G: The anthropic question: Fine tuning for life
One of the most profound fundamental issues in cosmology is the Anthropic question: why does the Universe have the very special nature required in order that life can exist?  The point is that a great deal of “fine tuning” is required in order that life be possible.  There are many relationships embedded in physical laws that are not explained by physics, but are required for life to be possible; in particular various fundamental constants are highly constrained in their values if life as we know it is to exist:

Ellis goes on to quote Martin Rees.

A universe hospitable to life—what we might call a biophilic universe—has to be special in many ways … Many recipes would lead to stillborn universes with no atoms, no chemistry, and no planets; or to universes too short lived or too empty to evolve beyond sterile uniformity.

Physics does not tell us anything (yet) about why the fundamental constants and other parameters have the values they do.  These parameters include, for example, the speed of light, the Planck constant, the four fundamental forces and their relative strengths, the mass ratio of the proton and the electron, the fine-structure constant, the cosmological density parameter, Ωtot, relative to the critical density, and so on.  And, why are there four fundamental forces?  Why not five?  Or three?

Also, why do we live in a universe with three spatial dimensions and one time dimension?  Others are possible—even universes with two or more time dimensions.

But it appears that only three spatial dimensions and one time dimension is conducive to life (at least life as we know it), as shown in the diagram above (Whittle 2008).

In fact, altering almost any of the parameters would lead to a sterile universe and we could not exist.  Is the universe fine-tuned for our existence?

Let’s assume for the moment it is.  Where does that lead us?

  1. As our understanding of physics advances, we will eventually understand why these parameters must have the values that they do. -or-
  2. We will eventually learn that some of these parameters could have been different, and still support the existence of life. -or-
  3. God created the universe in such a way that life could exist -or-
  4. We’re overthinking the problem.  We live in a life-supporting universe, so of course we find the parameters are specially tuned to allow life. -or-
  5. There exist many universes with different parameters and we just happen to find ourselves in one that is conducive to life. (The multiverse idea.)

#4 is the anthropic explanation, but a deeper scientific understanding will occur if we find either #1, #2, or #5 to be true.  #3 is problematic for a couple of reasons.  First of all, how was God created?  Also, deism has a long history of explaining phenomena we don’t understand (“God of the gaps”), but in time we are able to understand each phenomenon in turn as science progresses.

The anthropic explanation itself is not controversial.  What is controversial is deciding to what degree fine tuning has occurred and how to explain it.

In recent years, the multiverse idea has become more popular because, for example, if there were a billion big bangs and therefore a billion different universes created, then it should not be at all surprising that we find ourselves in  one with just the right set of parameters to allow our existence.  However, there is one big problem with the multiverse idea.  Not only do we have no physical evidence that a multiverse exists, but we may never be able to obtain evidence that a multiverse exists, due to the cosmological horizon problem1.  If physical evidence of a multiverse is not forthcoming, then in that sense it is not any better than the deistic explanation.

To decide whether or not there is only one combination of parameters that can lead to life we need to rule out all the other combinations, and that is a tall order.  Recent work in this field suggests that there is more than one combination of parameters that could create a universe that is hospitable to life (Hossenfelder 2018).

Thinking now about why our universe is here at all, it seems there are just two possibilities:

(1)  Our universe has a supernatural origin.

(2)  Our universe has a natural origin.

If our universe has a supernatural origin, then what is the origin of the supernatural entity (e.g. God)?  If, on the other hand, our universe had a natural origin (e.g. something was created out of nothing), didn’t something have to exist (laws of physics or whatever) before the universe came into existence?  If so, what created those pre-conditions?

In either case, we are facing an infinite regression.  However, we could avoid the infinite regression by stating that something has to exist outside of time, that is to say, it has no beginning and no ending.  But isn’t this just replacing one infinity with another?

Perhaps there’s another possibility.  Just as a chimpanzee cannot possibly understand quantum mechanics, could it be that human intellect is also fundamentally limited?  Are the questions in the previous two paragraphs meaningless or nonsensical in the context of some higher intelligence?

1We appear to live in a universe that is finite but very much larger than the region that is visible to us now, or ever.

References
G.F.R. Ellis, Issues in the Philosophy of Cosmology, Philosophy of Physics (Handbook of the Philosophy of Science), Ed. J. Butterfield and J. Earman (Elsevier, 2006), 1183-1285.
[http://arxiv.org/abs/astro-ph/0602280]

Sabine Hossenfelder, Lost in Math: How Beauty Leads Physics Astray (Basic Books, 2018).

M. J. Rees, Our Cosmic Habitat (Princeton and Oxford, 2003).

Mark Whittle, “Fine Tuning and Anthropic Arguments”, Lecture 34, Course No. 1830.  Cosmology: The History and Nature of Our Universe.  The Great Courses, 2008.  DVD.
[https://www.thegreatcourses.com/courses/cosmology-the-history-and-nature-of-our-universe.html]

Help Save WWV and WWVH!

Read these articles about the proposed elimination of radio time services WWV (Fort Collins, Colorado) and WWVH (Kekaha, Kauai, Hawaii) in 2019:

https://www.voanews.com/a/time-may-be-running-out-for-millions-of-clocks/4554376.html

https://www.nist.gov/director/fy-2019-presidential-budget-request-summary/fundamental-measurement-quantum-science-and

And please sign this petition by September 15:

https://petitions.whitehouse.gov/petition/maintain-funding-nist-stations-wwv-wwvh

WWV continuously broadcasts time signals at 2.5, 5, 10, 15, and 20 MHz, and WWVH does the same at 5, 10, and 15 MHz.

There are many uses for these radio stations.  For example, I have a shortwave radio in my observatory and use the WWV voice time broadcasts on 2.5, 5, and 10 MHz to make sure my GPS clock is properly synchronized, and also use it to set my computer clocks accurately and well as my wristwatch.

WWV and WWVH are an important and reliable “low tech” backup to the Global Positioning System (GPS) satellite constellation which can be used to derive accurate times.

Well over 50 million devices use the 60 kHz signal provided by WWVB to allow them to maintain accurate time, and eliminating this particular service would be devastating.  Whether or not shutting down WWVB is part of the proposed budget cuts remains to be seen.

These U.S. Government radio stations have been announcing accurate time since World War II.  We must do all we can to ensure their continued operation.

Black Hole Conundrums

Last night I re-watched the excellent two-hour PBS NOVA special Black Hole Apocalypse, and this time I jotted a few questions down.

  • Has Gaia DR2 improved our knowledge of the distance to the O-star black hole binary system Cygnus X-1 (6000 ly) and the mass of the black hole (15M)?
  • Are there any known pulsar black hole binary systems?
  • Could LIGO (and now Virgo in Italy) detect a stellar-mass black hole infalling into a supermassive black hole at the center of the Milky Way galaxy or another galaxy?
  • Do supermassive black holes play a role in galaxy formation?  If so, how does a supermassive black hole interact with dark matter?
  • Wouldn’t material infalling into a black hole undergo extreme time dilation and from our vantage point take millions or even billions of years to cross the event horizon?  If so, don’t all black holes—even supermassive ones—form from rapid catastrophic events such as core-collapse supernovae and black hole collisions?

Gaia DR2 (Gaia Data Release 2) has indeed measured the distance to the Cygnus X-1 system.  The “normal” star component of Cygnus X-1 (SIMBAD gives spectral type O9.7Iabpvar) is the 8.9-magnitude star HDE 226868.  Gaia DR2 shows a parallax of 0.42176139325365936 ± 0.032117130282281664 mas (not sure why they show so many digits!).

The distance to an object in parsecs is just the reciprocal of the parallax angle in arcseconds, but since the parallax angle is given in milliarcseconds, we must divide parallax into 1000.  This gives us a best-estimate distance of 2,371 parsecs or 7,733 light years.  Adding and subtracting the uncertainty to the parallax value and then doing the arithmetic above gives us a distance range of 2,203 to 2,566 parsecs or 7,186 to 8,371 light years.  (To get light years directly, just divide the parallax in millarcseconds into 3261.564.)

This is 20% to 40% further than the distance to Cygnus X-1 given in the NOVA program, and looking at the source for that distance (Reid et al. 2011) we find that the Gaia DR2 distance (7,186-8,371 ly) is outside the range given by Reid’s VLBA radio trigonometric parallax distance of 5,708-6,458 ly.  It remains to be seen what effect the Gaia DR2 distance, if correct, will have on the estimate of the mass of the black hole.

The estimate of the mass of the black hole in Cygnus X-1 is calculated using modeling which requires as one of its input parameters the distance to the system.  This distance is used to determine the size of the companion star which then constrains the scale of the binary system.  Because the Cygnus X-1 system is not an eclipsing binary, nor does the companion star fill its Roche equipotential lobe, traditional methods of determining the size of the companion star cannot be used.  However, once we use the distance to the system to determine the distance between the black hole and the companion star, as well as the orbital velocity of the companion star, we can determine the mass of the black hole.

Now, moving along to the next question, have any pulsar black-hole binary systems been discovered yet?  The answer is no, not yet, but the hunt is on because  such a discovery would provide us with an exquisite laboratory for black hole physics and gravity.  Something to look forward to!

Could LIGO ( and Virgo) detect a stellar-mass black hole infalling into a supermassive black hole at the center of the Milky Way galaxy or another galaxy?  No.  That would require a space-based system gravitational wave detector such as the Laser Interferometer Space Antenna (LISA)—see “Extreme mass ratio inspirals” in the diagram below.

http://gwplotter.com/

The above diagram illustrates that gravitational waves come in different frequencies depending on the astrophysical process that creates them.  Ground-based detectors such as LIGO and Virgo detect “high” frequency gravitational waves (on the order of 100 Hz) resulting from the mergers of stellar-mass black holes and neutron stars.  To detect the mergers of more massive objects will require space-based gravitational wave observatories (millihertz band) or pulsar timing arrays (nanohertz band) in the case of  supermassive black holes binaries within merging galaxies.  The future of gravitational wave astronomy looks very bright, indeed!

Do supermassive black holes play a role in galaxy formation?  Probably.  We are not yet able to explain how supermassive black holes form, especially so soon after the Big Bang.  Does dark matter play a major role?  Probably.  The formation of supermassive black holes, their interaction with dark matter, and their role in galaxy formation are all active topics or current research.  Stay tuned.

To succinctly restate my final and most perplexing question, “How can anything ever fall into a black hole as seen from  an outside observer?”  A lot of people have asked this question.  Here’s the best answer I have been able to find, from Ben Crowell:

The conceptual key here is that time dilation is not something that happens to the infalling matter.  Gravitational time dilation, like special-relativistic time dilation, is not a physical process but a difference between observers.  When we say that there is infinite time dilation at the event horizon we don’t mean that something dramatic happens there.  Instead we mean that something dramatic appears to happen according to an observer infinitely far away.  An observer in a spacesuit who falls through the event horizon doesn’t experience anything special there, sees her own wristwatch continue to run normally, and does not take infinite time on her own clock to get to the horizon and pass on through.  Once she passes through the horizon, she only takes a finite amount of clock time to reach the singularity and be annihilated.  (In fact, this ending of observers’ world-lines after a finite amount of their own clock time, called geodesic incompleteness, is a common way of defining the concept of a singularity.)

When we say that a distant observer never sees matter hit the event horizon, the word “sees” implies receiving an optical signal.  It’s then obvious as a matter of definition that the observer never “sees” this happen, because the definition of a horizon is that it’s the boundary of a region from which we can never see a signal.

People who are bothered by these issues often acknowledge the external unobservability of matter passing through the horizon, and then want to pass from this to questions like, “Does that mean the black hole never really forms?” This presupposes that a distant observer has a uniquely defined notion of simultaneity that applies to a region of space stretching from their own position to the interior of the black hole, so that they can say what’s going on inside the black hole “now.”  But the notion of simultaneity in GR is even more limited than its counterpart in SR.  Not only is simultaneity in GR observer-dependent, as in SR, but it is also local rather than global.

References
K. Liu, R. P. Eatough, N. Wex, M. Kramer; Pulsar–black hole binaries: prospects for new gravity tests with future radio telescopes, Monthly Notices of the Royal Astronomical Society, Volume 445, Issue 3, 11 December 2014, Pages 3115–3132, https://doi.org/10.1093/mnras/stu1913

Mingarelli, Chiara & Joseph W. Lazio, T & Sesana, Alberto & E. Greene, Jenny & A. Ellis, Justin & Ma, Chung-Pei & Croft, Steve & Burke-Spolaor, Sarah & Taylor, Stephen. (2017). The Local Nanohertz Gravitational-Wave Landscape From Supermassive Black Hole Binaries. Nature Astronomy. 1. 10.1038/s41550-017-0299-6.
https://doi.org/10.1038/s41550-017-0299-6
https://arxiv.org/abs/1708.03491

Jerome A. Orosz et al 2011 ApJ 742 84
https://doi.org/10.1088/0004-637X/742/2/84

Mark J. Reid et al 2011 ApJ 742 83
https://doi.org/10.1088/0004-637X/742/2/83

Brian C. Seymour, Kent Yagi, Testing General Relativity with Black Hole-Pulsar Binaries (2018)
https://arxiv.org/abs/1808.00080

J. Ziółkowski; Determination of the masses of the components of the HDE 226868/Cyg X-1 binary system, Monthly Notices of the Royal Astronomical Society: Letters, Volume 440, Issue 1, 1 May 2014, Pages L61–L65, https://doi.org/10.1093/mnrasl/slu002

Perseids Ahoy!

Already early this week you will see an occasional Perseid meteor gracing the sky, but next weekend the real show begins.  The absolute peak of this year’s Perseids is favorable to observers in North America, and with no moonlight interference we are in for a real treat—provided you escape cloudy weather.  I highly recommend “going mobile” if the weather forecast 24-48 hours before the peak night indicates less than ideal conditions at your location.

The Perseids this year are expected to peak Sunday night August 12/13.   Highest observed rates will likely be between 2 a.m. and 4 a.m. Monday, August 13.  Here’s a synopsis of the 2018 Perseids.

Fri/Sat
Aug 10/11
respectable activity
Sat/Sun
Aug 11/12
strong activity

Sun/Mon

Aug 12/13

very strong activity

Mon/Tue
Aug 13/14
strong activity
Tue/Wed
Aug 14/15
respectable activity

Neptune, the Mystic

Many years ago I wrote a short poem while listening to the final and most otherworldly section of The Planets by Gustav Holst: Neptune, the Mystic.

Here it is:

Neptune, the Mystic from The Planets by Gustav Holst
Royal Philharmonic Orchestra, Vernon Handley
Ambrosian Chorus, John McCarthy
Alto ALC 1013
The endless poetry of space
Sends shivers across my spine,
And there upon the threshold sounds
The now distant drone of time.
Music fills the spacecraft
Starlight fills the night,
And there upon the threshold think
I wonder, was I right?
David Oesper

 

The Planets was written by Holst between 1914 and 1916, and the premiere performance was at The Queen’s Hall, London, on September 29, 1918.  Adrian Boult conducted the orchestra in a private performance for about 250 invited guests.  The Queen’s Hall was destroyed by an incendiary bomb during the London Blitz in 1941, seven years after Holst’s death in 1934.

Pluto was discovered by Clyde Tombaugh in 1930, and was considered to be the ninth planet until its controversial demotion by the IAU in 2006.  A number of composers have added a Pluto movement to The Planets (“Pluto, the Renewer” by Colin Matthews, for example), and even an improvised performance (“Pluto, the Unpredictable”) by Leonard Bernstein and the New York Philharmonic.  I remember enjoying “Pluto, the Unknown” by American composer Peter Hamlin performed by the Des Moines Symphony in 1992, but unfortunately no recording of this work exists.

Largest Satellites of Our Solar System

Here is a table of the 12 largest satellites in our solar system.  In addition to the size of each satellite, its home planet, its median distance from that planet, and discovery information, its median distance from its home planet is given in terms of the median lunar distance from the Earth.  Remarkably, Pluto’s moon Charon is just 0.05 lunar distances from Pluto, only 19,591 km.  Only one other of the largest satellites orbits closer to its home planet than the Moon orbits around the Earth, and that is Neptune’s moon Triton at 92% of the Earth-Moon distance.  At the other end of the scale, Saturn’s moon Iapetus orbits Saturn over nine times further away than the Moon orbits the Earth.

Now let’s look at the orbital eccentricity of each of the largest moons, and the orbital inclination relative to the equator of its home planet.

Our familiar Moon is really an oddball: it has the greatest orbital eccentricity of all the largest satellites, and, with the exception of Triton and Iapetus, by far the greatest orbital inclination relative to the equator of its home planet.  Triton is the oddball among oddballs as it is the only large satellite in our solar system that has a retrograde orbit: it orbits Neptune in a direction opposite the planet’s rotation.  Iapetus has an orbital inclination relative to Saturn’s equator almost as much as the Moon’s orbital inclination relative to the Earth’s equator, but this anomaly can perhaps be forgiven because Iapetus orbits so very far away from Saturn.  Its orbital period is over 79 days.

Note that the Moon’s orbital inclination relative to the equator of the Earth varies between 18.33˚ and 28.60˚.  This occurs because the intersection between the plane of the Moon’s orbit around the Earth and the plane of the Earth’s orbit around the Sun precesses westward, making an entire circuit every 18.6 years.

Ganymede
Titan
Callisto
Io
The Moon
Europa
Triton
Titania
Rhea
Oberon
Iapetus
Charon

88 Constellations, One Musical Instrument

Of all the constellations in our sky, only one is a musical instrument: Lyra the Lyre.  A lyre is a stringed harplike instrument used to accompany a singer or reader of poetry, especially in ancient Greece.  One wonders what strange and lonely enchantments await the contemplative listener as Lyra wheels through our zenith these short summer nights.

Lyra crossing the celestial meridian at 12:06 a.m. CDT 15 Jul 2018 at 42°58′ N, 90°09′ W

Nova Scuti 2018

Nova Scuti 2018 (or N Sct 2018, for short) was discovered by prolific nova finder Yukio Sakurai of Japan on June 29, 2018.  His discovery image at 13:50:36 UT showed the nova shining at magnitude 10.3 (unfiltered CCD magnitude), using only a 180-mm f/2.8 lens plus a Nikon D7100 digital camera.  One of his many discoveries is named after him: Sakurai’s Object.

What is a nova?  A classical nova is a close binary star system that includes a white dwarf and a “normal” star.  The white dwarf siphons material off the other star until a critical density and temperature is reached in the atmosphere of the white dwarf, and a thermonuclear detonation occurs.

Nova Scuti 2018 will eventually receive a variable star designation (V507 Sct?).  Here are some typical nova light curves.

Nova Scuti 2018 is located fortuitously close to the 4.7-magnitude star Gamma (γ) Scuti.

Scutum Region (Source: Voyager 4.5)
Gamma Scuti Region (Source: Guide 9.1)

Here is a time sequence of images I’ve acquired of Nova Scuti 2018.  Comparing with the star chart above, can you find the nova?

Gorgeous Grieg

Edvard Grieg (Photo EGM0270, Edvard Grieg Archives at the Bergen Public Library)

Norwegian composer Edvard Grieg (1843-1907) is best known for his iconic Piano Concerto in A minor, op. 16, written in 1868 when the composer was just 24 years old, and his Peer Gynt suites, No. 1, op. 46 (1875, 1888), and No. 2, op. 55 (1875, 1891).  Like Tchaikovsky, Grieg had a gift for melody.

Grieg once wrote, “Artists like Bach and Beethoven erected churches and temples on the heights.  I only wanted to build dwellings for men in which they might feel happy and at home.”  With this in mind, you will find no better introduction to some of the other gorgeous music that Grieg wrote than Norwegian conductor Bjarte Engeset conducting Sweden’s Malmö Symphony Orchestra on Naxos 8.572403.

https://cps-static.rovicorp.com/3/JPG_500/MI0003/853/MI0003853098.jpg?partner=allrovi.com
Bjarte Engeset

Seldom have I found a disc of music so beautifully paced and played.  These five pieces for string orchestra (augmented by oboe and horn on “Evening in the Mountains”) followed by one piece for full orchestra provide the listener with over 71 minutes of pure enjoyment that will convince you (if you weren’t already convinced) that Grieg deserves a place alongside the most significant composers of the late 19th and early 20th centuries.  For me, personally, every one of these pieces is a favorite.  There is nothing to skip over here!

Naxos 8.572403

Two Elegiac Melodies, op. 34 (1880)
+ The Wounded Heart
+ The Last Spring

Two Melodies for String Orchestra, op. 53 (1890)
+ Norwegian
+ The First Meeting

From Holberg’s Time: Suite in Olden Style, op. 40 (1884)
+ Prelude
+ Sarabande
+ Gavotte
+ Air
+Rigaudon

Two Lyric Pieces, op. 68 (1897-1899)
+ Evening in the Mountains
+ At the Cradle

Two Nordic Melodies for String Orchestra, op. 63 (1895)
+ In Folk Style
+ Cow-Call & Peasant Dance

Lyric Suite, op. 54 (1905)
+ Shepherd Boy
+ Gangar
+ Notturno
+ March of the Dwarves

Don’t let words like “gorgeous” and “pure enjoyment” give you the impression that this music is lightweight fare.  There is a sadness in this beautiful music that evinces that it is anything but superficial.  Grieg and his wife Nina lost their only child, Alexandra, to meningitis when she was little more than a year old, Nina later miscarried a second child, and Grieg himself suffered all his adult life from the effects of pleurisy he had contracted when he was 17 years old.

Nina Grieg with her daughter Alexandra (Edvard Grieg Archives at the Bergen Public Library)

Caffau’s Star

A 17th-magnitude dwarf star in Leo 4,445^{+529}_{-427} ly distant has the lowest metallicity of any star yet discovered.  Stars with very low metallicity are designated as extremely metal-poor (EMP).

SDSS J102915+172927 (aka UCAC3 215-112497, UCAC4 538-051259, Gaia DR2 3890626773968983296, or just J1029+1729 for short) was identified by Elisabetta Caffau and her team in 2011 to have a global metallicity of Z ≤ 6.9 × 10-7 which means that the star is 99.999931% hydrogen and helium.  Looking at this another way, the global metallicity of our Sun is 0.0134 (98.66% hydrogen and helium), so Caffau’s Star has only about 1/19,000th the abundance of elements heavier than helium in comparison to the Sun.

Caffau’s Star   α2000 = 10h29m15.14913s   δ2000 = +17° 29′ 27.9267″

Metallicity is usually expressed as the abundance of iron relative to hydrogen.   It is a logarithmic scale.  [Fe/H] = 0.0 for the Sun; positive numbers mean iron is more abundant and negative numbers mean iron is less abundant than in the Sun.

[Fe/H] = +2.0 means iron is 100 times more abundant than in the Sun

[Fe/H] = +1.0 means iron is 10 times more abundant than in the Sun

[Fe/H] = -1.0 means iron is 1/10 as abundant as in the Sun

[Fe/H] = -2.0 means iron is 1/100 as abundant as in the Sun

And so on.  Caffau’s Star has an iron abundance [Fe/H] = -5.0, or 1/100,000th that of the Sun.  Caffau’s Star is the only EMP star with [Fe/H] < -4.5 thus far detected that is not a carbon-enhanced metal-poor star (CEMP).  In fact, Caffau’s Star has no detectable carbon!  Nor nitrogen.  Nor lithium.

Caffau’s Star is probably almost as old as our Milky Way galaxy.  In order to have survived for 13 Gyr, its mass cannot be any larger than 0.8 M.

References
Aguado, D.S., Prieto, C.A., Hernandez, J.I.G., et al. 2018 ApJL, 854, L34
Aguado, D.S., Prieto, C.A., et al. 2018 ApJL, 852, L20
Aguado, D. S., González Hernández, J. I., et al. 2017, A&A, 605, A40
Bonifacio, P., Caffau, E., Spite, M., Spite, F., François, P., et al. 2018
(arXiv:1804.10419)
Caffau, E., Bonifacio, P., François, P., et al. 2011, NAT, 477, 67