Other Ancient ImpactsPodcastPopular Press

Avi Loeb

Avi Loeb is no household name, but he wants to be. The chairman of the Department of Astronomy at Harvard has appeared on more than 50 podcasts since the start of the year. Given a minimum of one hour per podcast, I’d ask for a week’s pay back if I were Harvard. The guy is everywhere.

That’s OK in most instances, people pimp their books all the time. His new one is “Extraterrestrial“, where he documents in detail his intellectual courage, as he does on the podcasts.

But the Tusk thinks that Avi Loeb is probably a phony. Allow me to explain with two lines of reasoning.

First, Loeb’s gig, under development since 2019, is that cosmic interloper Oumuamua was perhaps an alien craft — not a comet. Due to his position at Harvard, the media immediately fell all over themselves given his ‘bold’ and ‘controversial’ claim.

A Harvard man and “aliens!” My word!!

The narrative, repeated again and again, was that Loeb was a intrepid scientist under fire for risky claims of aliens, particularly because he chairs a very prestigious institution.


I think his Oumuamua papers were a calculated grab at global media attention to Loeb, and little intellectual risk to him personally. The Tusk could not imagine a scientific claim less subject to the true tests of science: falsifiability and repeatability (also the best test of ‘reputational risk’ and thus intellectual bravery).

For purposes of practical science we are never, ever, going to see Oumuamua again. Loeb stands zero chance of being contradicted, much less embarrassed or humiliated.

When Galileo claimed the moons of Jupiter, (a man Loeb seemed to confuse with Copernicus on two podcasts), he probably knew that one day he was going to be tested on that moon thing. The public’s eyesight was only getting better. Or when Copernicus unseated us from the center of universe, he knew that others would gather data demonstrating or refuting earth’s modest placement.

That’s not Loeb. Loeb is not a risk taker. Risk takers can lose. But given the global media attention, Loeb has already won. That’s his gig. No one will ever see Oumuamua again.

M y second problem is Loeb’s appropriation of others’ ideas without proper citation or narrative credit. Which is particularly annoying to the Tusk. I am old friends with two octogenarian Brits who keep getting ripped off.

In my opinion, Loeb has lifted ideas without citation from Chandra Wickramasinghe and Bill Napier in order to establish intellectual priority before those two giants are finally vindicated by improved instrumentation (unless they are memory holed).

Here is a Pre-Covid Tusk post concerning Avi’s new interest in Panspermia: Claim Jumper: Avi Loeb and Amir Siraj poach ground long settled by Hoyle and Wickramasinghe 2/3/2020.

As far as I can tell, A. Loeb has published no astrobiological work before 2016. But now astrobiology is his gig. That’s fine, but to be respected over the long term you need the courageous humility to credit your predecessors. As far I can find, none of Loeb’s lectures, podcasts, papers or books make one mention of H-W’s role in his new discipline. Even if Hoyle and Wickramasinghe are wrong, they are key.

All this would be insufficient for a post, perhaps, but then I find out he is lifting other work from Bill Napier on the central subject of our blog: fragmenting comets in solar orbit. Here is some press from Loeb’s paper and also the paper.

A short-period fragmenting comet — outside earth’s atmosphere — a critical concept only now entering the public imagination — is the well established cause of the Younger Dryas Climate Crash. Bill Napier nailed it four decades ago, summarized here in 2010 and 2015. Loeb and Siraj take that same approach, but ignore short period comets, turn it into a even more unlikely long period comet, and manage to both accept and dismiss two critical aspects of the YDIE: 1) Accept a fragmenting comet, and 2) ignore those that may return regularly.

Martin Sweatman eat’s Siraj, Loeb et al.’s lunch

Here is Napier’s observation, shared with the Tusk, regarding Loeb. It’s a little dry, but:

The Siraj/Loeb paper fills a gap in the issue of comet disintegration as a terrestrial hazard, but the authors seem unaware of work already done in this area which likely vitiates their conclusions. The impact rates they derive for the fragments of long-period comets, one large impact per 250–730 million years or so, are probably in the right ballpark. However I can’t see why they neglect the arrival and disintegration of comets already close to the ecliptic plane, feeding in from the Centaur region.

They assume that tidal breakup is the only mode of disintegration of comets and give “the Encke complex” as an example. But tidal disruption only occurs within 0.01 au of the Sun whereas the perihelia of the Taurid complex objects are ~0.34 au. Thermal stresses on weak objects, exacerbated by rotational instability due to outgassing, are likely causes of disruption. If our current neighbourhood is typical (e.g. with the 10 km Hephaistos and other fragments of a ~100 km object), then the expected rate of arrival of large Centaurs may be sufficient to yield the observed rate of terrestrial large impacts. On this hypothesis the YDB events were triggered by the same external phenomena that yield mass extinctions on geological timescales.

The tidal disruption of a giant comet by Jupiter, enhancing the Jupiter family by orders of magnitude, is another possible source of hazardous impacts as yet unexplored Oort cloud comets are nevertheless a significant secondary hazard (Victor Clube and I thought they were the prime one before the discovery of the Centaur system). A long-period comet under the influence of Jupiter cycles in and out of a sungrazing orbit at intervals of a few hundred revolutions (the Kozai cycle). If the 100 km Kreutz sungrazer had been in a direct rather than retrograde orbit, its destruction would now be taking place near the ecliptic plane rather than well out of it, and we would now be immersed in a lot of hazardous stuff.

Bill Napier

As you can see, Bill is a gentleman. I think this is his gentle way of saying that Loeb et al. play with the ideas of others, get it partially wrong out of timidity, and do not credit their intellectual predecessors for what is right, which results in under estimating the true threat to humanity.

Loeb is the creepiest kinda scientist to venture into controversial fields. He has the big credentials, professes some big ideas consistent to some degree with popular fringe theories which excite the public, but reaches only timid conclusions which are inconsistent with the true science. Just wild enough for the press — minus true bravery.

Ironically, it’s good to have Avi introduce fragmenting comets into the public and press’ mind. But why fragmenting comets only from deep time, and not the extensively published claim of one such beast just 13,880 years ago? What has Loeb said about the very well published Younger Dryas Event? Just one word? There have been hundreds of papers — and it’s in his “wheelhouse.” Just like DeGrasse Tyson

With regard to Panspermia, if Loeb is going to make the furthest most accepted claims about Panspermia, how about ruling out — or at least acknowledging — the published understandings of the fathers of your newfound field?

As I said at the top, I think Loeb may be a redeemable creep. My evidence he’s a turd is circumstantial. I have enjoyed listening to Avi at times, impressed with his science communication ability and optimism. Unless the world of science just continues to disintegrate, Loeb could pivot just a tad, make it right, and improve his reputation long term at little cost by adding a couple of citations in future papers, and a word or two.

Maybe if he reads this post that will happen, or he can let us know why it shouldn’t. In an ideal world of science communication he would re-join my respected friend Micah Hanks’ Podcast and answer some real questions. Perhaps brilliantly.

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