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Sabine Hossenfelder
@skdh
, 10 tweets, 3 min read Read on Twitter
As we celebrate the 100th anniversary of the first test of #Einstein's theory of General Relativity by deflection of light on the sun, let us not forget that 200 years ago the effect was thought to be unobservably small.

backreaction.blogspot.com/2015/04/a-wond…
This estimate was possible because a similar effect should also take place in Newtonian gravity, just smaller by a factor of two. This was derived in 1801 by the German astronomer Johann Georg von Soldner.

de.wikisource.org/wiki/Ueber_die…
Soldner was well aware that the effect he calculated was miniscule, but refused to apologize. He wrote:

"Incidentally I do not think it should be necessary for me to apologize that I publish this article even though the result indicates that the deviation is unobservably small."
and continued

"We must pay as much attention to knowing what theoretically exists but has no influence in practice, as we are interested in that what really affects practice. Our insights are equally increased by both."
Sure enough, 120 years later, technology had advanced sufficiently for Eddington to be able to measure the effect. At least in principle. In practice, the error on his measurement was so large it was strictly speaking inconclusive.
By the 1990s, one didn’t have to wait for solar eclipses any more. Data from radio sources, such as distant pulsars, measured by very long baseline interferometry (VLBI) could now be analyzed for the effect of light deflection.
In 1991, Robertson, Carter & Dillinger confirmed to high accuracy the light deflection predicted by General Relativity by analyzing data from VLBI accumulated over 10 years.

nature.com/articles/34976…
A wonderful update on this measurement comes from two Australian astronomers who analyzed the VLBI data from some selected radio sources over a period of 10 years. Paper is here:

arxiv.org/abs/1502.07395
In the image below, you can see how the apparent position of the blazar (1606+106) moves around over the course of the year due to light deflection on the sun. Each dot is one measurement point; the “real” position is marked zero on the axes.
How is this for an effect that was thought to be unobservable 200 years ago?

I think this holds a lesson for quantum gravity. Those saying now the effects are unobservably small will be proved wrong 200 years from now.
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Sabine Hossenfelder
@skdh
Tomorrow (April 10) at 3pm CEST (9am Eastern Time) the first results from the Event Horizon Telescope (EHT) will be announced:

eso.org/public/announc…

What to expect? /begin thread

(Image: Screenshot from this video: )
The scientific mission of the Event Horizon Telescope is to capture an image of a black hole horizon. So far, we have indirect evidence for the existence of a black hole horizon, but have not actually “seen” one. 1/
You cannot really “see” a black hole, but you can see the way that a black hole wraps light around its horizon. It is a very strong lensing effect, not entirely unlike to the warped lensing that you can create with some photo apps. (Image: Artist's Impression of black hole) 2/
Read 14 tweets
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Sabine Hossenfelder
@skdh
True story about exam anxiety: 10+ years ago I was a teaching assistant ("tutor") for undergrad physics lectures, responsible for a group of about 12 or so, 2 of which women (for what I recall now). 1/
Exam time nears. This one is an important qualification test, deciding about whether the students will be admitted to advanced classes and can write their master’s thesis. 2/
One of the women in the class is an A+ student. I am perfectly sure she’ll ace her exam. But she has bad exam anxiety, the totally destructive “will faint” type. I do my best to reassure her, but don’t really know how to help her. 3/
Read 11 tweets
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Sabine Hossenfelder
@skdh
“Arguments” for a bigger particle collider that I’m sick of hearing (thread)
1) So-and-so many billions is only such-and-such a tiny amount per person per day.

Yes, right. Same with any other billion-dollar investment. So your point is what?
2) Tim Berners-Lee invented the www while employed at CERN.

Yes, right. But he (and others) had been thinking about such technology before that, and if not then and there, it’d have happened soon elsewhere.
Read 11 tweets

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🦁 Leo C. Stein
@duetosymmetry
Exactly 100 years ago today, the Moon's shadow passed directly over the Earth: a total solar eclipse. On that fateful day, several astronomers were working to photograph the stars by the edge of the sun at the moment of totality. This observation would rocket Einstein to fame. 1/
In Newton's theory, there is no reason for light to be bent by gravity. You can, however, derive some amount of bending by appealing to conservation of energy. But that amount of bending is also wrong. The right answer comes from Einstein's theory of general relativity. 2/
By May 1919, Einstein's theory (GR) had already been published for two and a half years. It had seen an early astronomical success in Einstein's calculation of how fast Mercury's orbit precessed around the Sun: 43 arcseconds per century more than in Newton's theory. 3/
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Dr Rachael Livermore
@rclivermore
Good morning Nerd Twitter! Today is the 100th anniversary of the 1919 solar eclipse that Eddington used to confirm Einstein’s theory of General Relativity. A 🧵
For those who aren’t familiar with General Relativity (GR), it’s really just a rethinking of how gravity works. Instead of the Earth magically knowing about the mass of the Sun from a distance, GR says the Sun (& anything with mass) curves the space around it (2/)
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Ben Becker
@benbecker_
The project to take a single picture of a black hole 55 millions years away cost $60 million. There's no immediate profit to be made from the discovery. It couldnt have happened if the scientists had to justify their work on the basis of commodities to be sold on the market
Or if they were beholden to private investors & quarterly earnings reports. It required public funding to liberate science from the bounds of profit. Or it wouldnt have happened. Nor could it have happened without deep international coordination (including with Russia and China)
While we can take pictures of previously unseeable things, 55 million light years away, global capitalism can't get all the abundance of food into the world's hungry bellies, all the homeless into empty homes, & how to guarantee the conditions of existence as social rights.
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Bansi Sharma
@bansisharma
Black Hole
Astronomers have captured the first image of a black hole, heralding a revolution in our understanding of the universe’s most enigmatic objects.
The breakthrough image was captured by the Event Horizon Telescope (EHT), a network of eight radio telescopes.
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Black holes are so small, dark and distant that observing them directly requires a telescope with a resolution equivalent to being able to see a bagel on the moon. This was once thought to be an insurmountable challenge.
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Adam
@Khanoisseur
1. QI (proposed physicist Mike McCulloch) is so controversial because it abandons dark matter and Einstein’s equivalence principle: The inertial mass of an object is no longer coupled to its gravitational mass and is instead explained by effects of Unruh radiation on the object.
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