Hanukkah, Thanksgiving and the Drake Equation

I recently finished celebrating Thanksgiving and Hanukkah with my family; enjoying the wonderful meal, lighting the 2^nd Hanukkah candle and thanking God both in English and Hebrew. Following this, we also prepared to celebrate the end of the semester, and got ready to welcome Christmas, the New Year, and our wedding anniversary. What a busy time!!

The emergence of Thanksgiving on the same date as the start of Hanukkah was another occasion to commemorate. The media was full of coverage for the event, reminding us that the next time the two events coincide will be in about 70,000 years. An example of such coverage is given below:

It’s a once in more than 70,000-year event: The first day of Hanukkah this year coincides with Thanksgiving. As a result, Jews everywhere are gearing up for “Thanksgivukkah,” a mashup of Thanksgiving and the Jewish festival of lights. This lineup of the first day of Hanukkah with Thanksgiving is incredibly rare.

“That’s not going to happen again for thousands and thousands of years. No one knows exactly how long, because the calendars aren’t going up that high,” said Jason Miller, a rabbi in Michigan who blogs at rabbijason.com. “It’s something like 70,000 years,” assuming of course that America, the Jews and the human race are still around at that time.

Well, digging a bit deeper into this issue reveals that the emphasis should be on the first day of Hanukkah. Hanukkah is celebrated for eight days, and the name “Thanksgivukkah,” could be applied to the coincidental timing of any of Hanukkah’s days with Thanksgiving. A more detailed data set is given below:

This is an entirely different estimate in terms of timing. I was alive for the previous two events (Texas Only), even though, at the time I knew nothing about Thanksgiving. The next one, meanwhile, coincides with my definition of “now” in the title of my book, where “now” refers to the projected lifespan of my grandchildren, and indicates the likely stretch of the global impact of climate change. The different spelling for Hanukkah in the two entries is not unusual for words that have been transliterated from other languages.

The fluctuations in the timing of the holidays are rooted in the two different calendars by which their respective communities (US and Jewish) determine the dates, as well as the continuous adjustments by said communities to make sure that these holidays fall approximately in their appropriate seasons. Thanksgiving, for example, is celebrated on the last Thursday in November (or the fourth Thursday in November), and is dictated by the Gregorian calendar. Hanukkah is based on the lunar-based Hebrew calendar.

In terms of future coincidental timing – while I will not live to see any of them, my grandchildren have decent statistical chances of seeing the next one (it won’t be the same, but 1^st candle will have to do).

What caught my eye is that the desire to see the coincidental timing can serve as an inspirational target for at least some of us. In this sense, Thanksgivukkah might become an essential part of Astrobiology: “the study of the origin, evolution, distribution, and future of life in the universe: extraterrestrial life and life on Earth.” The search for places that are suitable for extraterrestrial life is a fascinating topic to study – not just for the intellectual curiosity that is involved, but also as an existential challenge, or plan B, in case we help to make our planet unlivable. Recently, Stephen Hawking addressed the issue:

TORONTO – Stephen Hawking says the colonization of outer space is key to the revival of humankind, predicting it will be difficult for the world’s inhabitants “to avoid disaster in the next hundred years.”

In 2009, James Cameron found such a place on a planet named Pandora that circles our nearest neighbor, a pair of stars named Alpha Centauri A and B. Alpha Centauri are real stars. The distance from earth to these stars is 4.4 Light Years (LY) or 25 trillion miles (42 trillion km).

Recently it was discovered that there is a real planet that orbits Alpha Centauri B that is very similar to Earth in terms of mass, but given its surface temperature of about 1200⁰C, it is not a habitable planet. Could James Cameron have filmed Avatar on site? Not likely. The present record space speed by a satellite belongs to Helios 2, which orbits the Sun. With the help of the sun’s gravity, Helios 2 was able to attain a speed of 241,000km/hr. Voyager 1 attained the fastest solar escape velocity at 62,120km/hr. If we take the present fastest man-made space vehicle to be around 200,000km/hr, the time that it would have taken James Cameron to reach Pandora would have been 20,000 years. There is a continuous effort to develop better space propulsion systems, but an average schedule for reaching the “practical” space speed necessary to be able to move people around is still estimated at 1,000 years. The effort to actually find a suitable home for extraterrestrial (or our own) life got a serious boost with the advent of NASA’s Kepler mission.

The effort to find extraterrestrial life goes way back. In the 1950s and 60s, when we didn’t have today’s technology, we had an abundance of UFO sightings (Unidentified Flying Objects). I have discussed some of the consequences in previous blogs (January 28 and February 4) in terms of the Fermi Paradox and the Physics of Sustainability.

In Early 1961, a young Astrophysicist, Frank Drake, organized a small conference to address the issue of trying to detect extraterrestrial intelligence. The story goes that he went to the blackboard and scribbled an equation. Since then, the equation has become almost as popular as E = mC². Every course that even mentions the issue of extraterrestrial life starts with the equation. A sample on a t-shirt is shown below

₌₌

A more readable form, including an explanation of each of the terms follows:

N = the number of civilizations in our galaxy with which radio-communication might be possible

R_* = the average rate of star formation in our galaxy

f_p = the fraction of those stars that have planets

n_e = the average number of planets that can potentially support life per star that has planets

f_l = the fraction of planets that could support life that actually develop life at some point

f_i = the fraction of planets with life that actually go on to develop intelligent life (civilizations)

f_c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L = the length of time for which such civilizations release detectable signals into space^[8].

There is obviously a large uncertainty in most of the terms. The most interesting term for our use is L. Since we are the only advanced technological civilization that we are aware of, the best place to start our estimates of the lifetime of such society is here on earth. Such an estimate is not some astronomical constant that we just have to find a smart way to measure. The value depends on our collective actions. This will be true for any advanced civilization.

This is not just a speculative exercise that physicists can design to confuse everybody else. It provides a timeline to govern our activities and thus explore what I have defined before (February 4 blog) as an absolute scale of sustainability.

In the next few blogs I will try to use that timeline to work out some of the details, starting with the requirements for population growth (or limitation therein).