@ChristineMalec Thank you!

Humans first set foot on the Moon #OTD in 1969.

Images: NASA

Physicist Leo C. Stein (@duetosymmetry) was born #OTD in 19-mumble-mumble. He is best known for his work on general relativity and almost-relativity theories of gravity, especially astrophysical tests and numerical methods, and his support and mentoring of young researchers.

Leo is one of those young physicists who somehow seems to know a lot about... everything. It feels like he is announcing a new paper weekly, which, leave some problems for the rest of us to solve.

https://duetosymmetry.com

Midweek bunny update.

SOMEONE climbed up on the table and cleaned out my daughter’s bowl of spaghetti with meat sauce, then finished off a bag of shredded parmesan. No witnesses, unfortunately. But I have my suspicions.

Good morning.

@mmoore We didn’t, hopefully? But we don’t need google suggesting to folks that a speculative result is on equal footing with the consensus answer.

That isn't necessarily what's happening.

I have a google scholar profile, so it may think I want to see new research results.

Maybe it is just serving results based on location, or the fact that I recently clicked on a link to a story about this study. Lots on non-nefarious possibilities!

But something like this still gives me pause! For a scientific question, I don't like the idea of google giving me one answer when it thinks it can see who I am, and a different answer when it can’t.

One reason to worry about this is the possibility that google is using tracking info to decide what response it should serve.

That makes sense for some queries, but not for a scientific question with a consensus answer.

For example, if google decides based on browsing that someone is anti-vaccine, and the person asks how best to protect their kids from measles, how will it respond?

Will you get medical consensus, or a "study" that hasn't been around long enough for serious review?

If anyone is wondering how google is doing, it is giving incorrect answers to the query “How old is the Universe?”

Instead of serving up scientific consensus (just shy of 14 billion years) it is latching onto recent media coverage of a questionable study (tired light, time-dependent coupling constants) claiming a much larger figure.

Notably, it gives me the right answer from an incognito window. But elevating popularity metrics over scientific consensus is a real problem!

Good evening.

@stacylwhitman Something that evokes Gorey’s illustrations for Eliot’s “Old Possum's Book of Practical Cats”

@Rog Not stupid at all! Ultimately physics is an experimental science, and speculative ideas need to have observable consequences so they can be tested. Physicists spend lots of time trying to work out how to do this for various proposed ideas.

One pretty well accepted idea about this earlier phase is that it involved a period of “Cosmic Inflation.” Inflation predicts statistical patterns for small variations in the cosmic microwave background which we have observed.

"The whole matter of the world may have been present at the beginning, but the story it has to tell may be written step by step."
— Georges Lemaître

The last paragraph of Lemaître's 1931 paper is a poetic rumination on determinism in a Universe that has a beginning, and is described by physical laws.

It sings to me.

Lemaître doesn't say anything about quantum gravity. But he does insist that notions of space and time must fail to have meaning during this phase. That is a very sophisticated idea for 1931!

Notice that there is no mention of a “beginning” here. The hot Big Bang appreciates that our physical theories have limits.

The other notion of "Big Bang" is that the Universe has a definite beginning, by which I mean a describable phase before the hot Big Bang.

What this early phase might be isn't clear; we all have our speculations. Most physicists agree that these questions are the province of quantum gravity.

First, the "hot Big Bang" is the idea that if we follow the evolution of the universe backwards, we necessarily arrive at a very hot, dense, and energetic early phase.

Our physical theories can be pushed to very high energies and densities, but they only allow us to extrapolate back so far.

You run the clock forward from there and find that much of what we see in the universe (cosmological expansion, CMB, primordial abundance of elements, etc) follows from that.

Many years later, in 1949, Fred Hoyle would dismissively refer to models of this sort as beginning with a "Big Bang."

Hoyle was a staunch opponent of the idea that the Universe could have a beginning. He was defending his Steady State Theory on the BBC, and criticized “the hypothesis that all matter of the Universe was created in one big bang.”

Nowadays, there are two main ways that the term "Big Bang" is used. Lemaître's original idea shares features with both of them.

In 1931, Lemaître pursued a radical line of thought. He ran the clock of his expanding Universe model backwards and concluded that there must be some sort of beginning.

This would be an extremely dense and energetic phase which he described as "very different from the present order of Nature."

In a short letter published in Nature, Lemaître used the terms “unique quantum" and "unique atom” to refer to this hypothetical early state.

His letter is available here: https://www.nature.com/articles/127706b0.pdf