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Jonah Miller
25,793 followers -
A physics Ph.D. student. I simulate black holes and write about physics and math.
A physics Ph.D. student. I simulate black holes and write about physics and math.

25,793 followers
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The Long Arms of the Black Hole

Black holes are incredibly messy eaters. As matter falls into a spinning black hole, that matter can be accelerated to incredible velocities and launched out the poles. In the case of the supermassive black holes at the centers of galaxies, these are the most energetic events in the universe since the Big Bang.

The exact mechanism for the creation of these jets is unknown. There are two competing theories, one called the Blandford-Payne mechanism, and one called the Blandford-Znajek mechanism. The details are too fiddly to get into here, but the former has more to do with the in-falling matter and the latter has to do with how magnetic fields interact with the spinning black hole.

The image bellow is of the galaxy Centaurus A and the jets produced by its super-massive black hole, which is fifty five million times the mass of our sun. The white glow and brown disk are the galaxy itself and associated dust cloud respectively. The blue line is the ultrarelativistic jet of material emitted by the black hole. (Actually, it's the X-rays emitted by the fast-moving matter in the jet.)

You can't see the black hole at all. Even on the scale of a galaxy, it's just a dot, smaller than a pixel. But it has a wide wide reach, extending far beyond the galaxy and influencing the growth and evolution of the galaxy profoundly.

(The image is actually the composite of three images. From Wikipedia: This is a composite of images obtained with three instruments, operating at very different wavelengths. The 870-micron submillimetre data, from LABOCA on APEX, are shown in orange. X-ray data from the Chandra X-ray Observatory are shown in blue. Visible light data from the Wide Field Imager (WFI) on the MPG/ESO 2.2 m telescope located at La Silla, Chile, show the background stars and the galaxy’s characteristic dust lane in close to "true colour".)

Image Source: https://en.wikipedia.org/wiki/Centaurus_A

Related Reading

These objects are called active galactic nulcei. See: https://en.wikipedia.org/wiki/Active_galactic_nucleus

Black holes glow for other reasons too. They have so-called accretion disks, which glow incredibly brightly. I wrote about this a while back: http://www.thephysicsmill.com/2013/11/09/accretion-disk/

The bottom line is this: We can see black holes.

#physics #astrophysics #science #blackholes #spaceporn   #scienceeveryday  
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I am at the Dulles airport returning from the April APS meeting in Washington DC (I know. It's in January this year).

The meeting pretty exactly coincided with Trump's executive order regarding immigration. We at the meeting were all shocked and many speakers (invited and otherwise) expressed their shock, sadness, and concern.

This was not a normal physics meeting. Many of the talks had titles like "The complicity of scientists in Nazi Germany" and "Physics in the age of populism."

We came to the meeting as scientists. But we also came together and acted as people, concerned for our friends and colleagues who are in danger of discrimination or who have already suffered from the immigration ban.

I'm saddened and shocked by pretty much everything Trump has done this week. But I am at least heartened by the outpouring of feeling, and of action and support, by the community that I am part. The physics community is not perfect. But in this, at least, we seem to be united.
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Artillery at the End of the World

This artillery was placed in the city of Ushuaia (at the southern tip of Argentina) during a short-lived border conflict between Argentina and Chile in 1978. It was dragged to the top of the hill by oxen in case of an attack on the city. When the conflict was peacefully resolved, the gun was simply abandoned.

For reference, the conflict was the Beagle conflict: https://en.wikipedia.org/wiki/Beagle_conflict
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Abandoned Hotel at Lago Escondido

I previously posted about Ushuaia, the city at the end of the world. It is at the southernmost tip of Argentina and it is the sourthernmost city in the world.

A few hours drive from Ushuaia is Lago Escondido, a beautiful and picturesque lake born from plate tectonic motion. On the shore of Lago Escondido lies Hosteria Petrel, Tierra del Fuego. This hotel was once a flourishing resort. However, because it was built too close to the lakeshore it was closed down and eventually abandoned.

I had the good fortune of riding in a souped up car to the shore of Lago Escondido and exploring Hosteria Petrel. Here's some photos from that experience. 
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12/31/16
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The Boulevard at the End of the World

Like most people, I visit my family over the holidays. This holiday season, however, I didn't fly home to Colorado. I boarded a plane bound for Buenos Aires, Argentina, where I met my parents. And from there, we flew to the southernmost city in the world: Ushuaia. In two days, we board a ship bound for Antarctica.

Ushuaia calls itself the end of the world, and it feels like it. The mountains meet the sea and the skies are grey or cold blue. The sun sets at 10:30 pm and only for a few hours.

There is an amazing variety of birds, none of which seem too bothered by humans. In my short time here I've seen: hawks, seagulls, geese, penguins, swans, turns, cormorants, and a huge number of small songbirds.

I haven't seen any non-domestic landwalking animals, but the sea life is also incredible. Yesterday I saw sea lions and a juvenile humpback whale.

In two days, I will lose all internet access as I travel to Antarctica. But until then, checking in from the end of the world!
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Fin du Monde
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If we can't predict the weather next month how can we predict climate change?

The answer is hidden in chaos theory.

This is a common misconception about how climate models work and this post is inspired by a question in the +Science on Google+​​​ community.

The climate is a so-called "chaotic system." See:
https://en.m.wikipedia.org/wiki/Chaos_theory

One simple example of a chaotic system is the Lorentz attractor:
https://en.m.wikipedia.org/wiki/Lorenz_system

In a chaotic system, the behaviour of the system at any given time is very hard to understand. This is why we can't predict the weather very well.

But look at the movie of the Lorentz attractor below. Notice anything?

The particle moves all over the place. The motion is very hard to predict. But it's usual or average position is predictable! The particle is usually along those curves!

This is typical of chaotic systems and the climate is the same way. We can't predict the weather next week. But we can predict the general behavior of the average weather over many years. And this is why you should trust predictions about climate change.

The science is definitive. Global average temperatures are getting warmer and this is caused by human activity.

See:
http://climatechangeconnection.org/science/how-can-we-predict-climate/
http://www.skepticalscience.com/weather-forecasts-vs-climate-models-predictions.htm
http://www.climatecentral.org/library/faqs/if_we_cant_predict_weather_two_weeks_ahead_how_can_we_predict_climate
http://science.howstuffworks.com/nature/climate-weather/atmospheric/scientists-predict-weather.htm
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An Explanation for the EM Drive? Probably not.

This news is a little old, but you may have seen an article claiming that scientists might have come up with an explanation for the EM drive. One such article, which does a good job summarizing the situation, is this one:
http://futurism.com/?p=42244&post_type=link

The paper it references is peer-reviewed and open-access. You can find it here if you're interested. I worked through it.
http://scitation.aip.org/content/aip/journal/adva/6/6/10.1063/1.4953807

As the article (and Google plus's very own +Brian Koberlein​​​​​​​​​​) say:

the new paper re-interpret's the quantum vacuum in such a way that the em drive is not reactionless, it emits light.

So what does this mean?

The vacuum

Empty space isn't really empty. Rather it's buzzing with all sorts of particles that appear and disappear very quickly, as permitted by the Heisenberg uncertainty principle. These particles are always created in pairs of particles and antiparticles so that momentum, for example, is conserved.

In essence, the claim is that the electric field provided by the em drive pushes some of these particles out the back of the drive and leaves others inside, breaking up the pairs.

+Brian Koberlein​​​​​​​​​ ​mentions the "Unruh effect," where this happens because of acceleration. And most people know about Hawking radiation where this happens because of the gravity due to a black hole.

Implications

So if the claim is true, this would mean the device does not violate Newton's laws. And it's not "impossible" after all.

On the other hand, it would also mean a more efficient form of thrust would just be to attach a bunch of LEDs to the back of your spaceship.

This would also put an upper bound on the power and efficiency of the drive to be the same as other light-based devices. It could not get us to mars in 40 days.

The claim would, in other words, explain the em drive but also immediately make it obsolete.

Reasons to be Sceptical

The journal article in question is not even a little bit quantitative. There are no calculations in it whatsoever. It's essentially just an argument, in words that the em drive could be caused by an effect like this.

That's not how science is done and, to be honest, I'm annoyed this article got through peer-review. If I had reviewed this article, I would not have recommended it for publication. It's not a theory until it makes a quantitative, testable prediction.

And even if the prediction isn't testable, the authors should back up their ideas with some kind of calculation. Mathematics are how theoretical physicists keep themselves honest. It's much harder to fool oneself with maths than with words.

It's plausible that an effect like the Unruh effect and Hawking radiation could, maybe create an effect like the em drive, but the only way to tell is to do some math and make a prediction. And the authors of this paper did not do that.

So let me be clear.

This paper is interesting but it is neither an authoritative explanation for the em drive nor proof that it works. This isn't even a theory.

Conclusions

As the article said. If something seems too good to be true, it probably is.

In my opinion, the EM drive probably doesn't need an explanation because it probably doesn't work. We don't ask people to explain how broken chairs work.

Other stuff

Thanks to +Derek Adjei for linking to this article in the +Science on Google+ community.

Full disclosure, my discussion here is a copy-paste of my comment in the original post:
https://plus.google.com/111703555314098217990/posts/5GYXLoV1MFq

Image is the EM drive inventor, Roger Shawyer. Credit due to Roger Shawyer, Satellite Propulsion Research Ltd via IBTimes (http://www.ibtimes.co.uk/emdrive-nasa-eagleworks-confirms-paper-controversial-space-propulsion-under-peer-review-1551210)
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Cactus

At a workshop on Trento Italy for the +Einstein Toolkit​, based on the Cactus computational toolkit, we found a real cactus! And now I'm new Mexico, I found another one. (The second one may be in a more likely location.)

This may be of interest to +Erik Schnetter​ ​ and +Bruno Giacomazzo​
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6/26/16
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Tent Rocks National Monument

This beautiful and bizarre place is about half an hour out of Santa Fe NM.
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Now gravitational waves detected! Again at 5 sigma.
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