Of Particular Significance

Tag: cms

Though I’ve been busy with a number of physics and writing tasks, I’ve been beefing up the “Reader Resources” section of this website, devoted to extending the experience of readers of my book. [BTW, the audiobook is due out at the end of September.]

The book has many endnotes (available separately here, in case [like me] you hate paging back and forth between the text and the endnotes, and would like to have the endnotes more easily available on a separate screen.) A number of these endnotes have asterisks, and for those endnotes I promised to provide more information here on this website. Well, that information is going up, step by step.

For example:

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON August 20, 2024

[Update: indeed, both meteors and auroras are visible tonight, at least as far south as Massachusetts, so residents of northern-tier states should definitely be looking!]

Tonight, if the sky is clear and dark in your vicinity, would be a good night for staying up late, going outside, and looking up. Not that it’s an exceptional night for star gazing, necessarily; I wrote “sky-gazing” for a reason. The two phenomena you’re most likely to see are much, much closer than the stars. Both occur in the Earth’s upper atmosphere, and are generated by effects that occur within the solar system (i.e., the Sun, its planets, and their neighborhood.)

The phenomena in question? Meteors, for sure; and auroras, just maybe.

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON August 11, 2024

[Update July 30 8:00 am NYC time: there was a weak impact of a coronal mass ejection about 12 hours ago, but nothing big yet.]

After a few significant solar flares over the past few days, the chances of auroras (i.e. northern and southern lights) is high enough that it’s probably worth keeping an eye on polar skies for the next couple of nights. At the moment the forecast is for the best chances to be in Asia, but forecasting auroras is far from an exact science, and there could be surprises.

The Aurora Borealis, or Northern Lights, shines above Bear Lake, Alaska. USAF photo: credit Senior Airman Joshua Strang

To know when to start looking, I keep an eye on data from the ACE satellite.  When a cloud of slow particles from a solar flare’s coronal mass ejection arrives, ACE’s data goes all haywire; you’ll see it as a sudden change in the plots’ appearance, as in the example shown below. ACE satellite sits 950 thousand miles [1.5 million kilometers] from Earth, and is located between Earth and the Sun.  At that vantage point, it gives us (and our other satellites) a little early warning, of up to an hour.

Another good place to look is NOAA’s space weather dashboard. Its first panel, an example of which is shown below, displays three plots; the bottom plot is called “Geomagnetic Activity”. When that plot goes deep orange or red, then there’s probably some serious auroras going on in areas where they aren’t so often seen.

But be warned — the plot shows not what is happening now but what happened in a three-hour interval that is already past. If a geomagnetic storm is long enough, that’s still useful, but be aware that the data is out of date by the time we get to see it. That’s why the ACE satellite may well give you the best heads-up.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 29, 2024

As has been widely reported, Earth’s inhabitants are looking forward to a rare event in the sky. It’s a “nova”, predicted to be visible sometime in the coming weeks.

The word “nova” is simply Latin for “new.” Coined during the Renaissance, it initially meant “a new bright thingy in the sky that isn’t just another Starlink satellite.” Nowadays it means a very particular type of new bright thingy.

But let’s not confuse it with a “supernova.” That’s something different. How different?


  • Nova: Your house has an electrical blackout for an hour
  • Supernova: Your entire city goes dark for a week

  • Nova: A meteor kills the dinosaurs and lots of other creatures
  • Supernova: A meteor melts the Earth and blasts part of it skyward to create the Moon

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 29, 2024

Every now and then, I get a question from a reader that I suspect many other readers share. When possible, I try to reply to such questions here, so that the answer can be widely read.

Here’s the question for today:

Below I give a qualitative answer, and then go on to present a few more details. Let me know in the comments if this didn’t satisfactorily address the question!

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 25, 2024

The mass of a single proton, often said to be made of three quarks, is almost 1 GeV/c2. To be more precise, a proton’s mass is 0.938 GeV/c2, while that of a neutron is 0.939 GeV/c2.

But the masses of up and down quarks, found in protons and neutrons, are each much less than 0.01 GeV/c2. In short, the mass of each quark is less than one percent of a proton’s or neutron’s mass. If a proton were really made from three quarks, then there would seem to be a huge mismatch.

(Here and below, by “mass” I mean “rest mass” — an object’s intrinsic mass, which does not change with speed. It is sometimes called “invariant mass”. [Particle physicists usually just call it “mass”, though.])

Part of the explanation for the apparent discrepancy is that a proton or neutron is, in fact, made from far more than just three quarks. In its interior, one would find many gluons and a variety of quarks and anti-quarks. However, that doesn’t resolve the issue.

  • Gluons, like photons, have zero rest mass, so they don’t help at all, naively speaking.
  • The typical number of quarks and anti-quarks inside a proton, while more than three, is too small to add up to the proton’s full mass;

And thus one cannot explain the proton or neutron’s large mass as simply the sum of the masses of the objects inside it. The discrepancy remains.

Moreover, as can be verified using either strong theoretical arguments in analogous systems or direct numerical simulations, protons and neutrons would still have a substantial mass even if the quarks and anti-quarks they contain had none at all! Mass — from no mass.

Clearly, then, the solution to the puzzle lies elsewhere.

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 22, 2024

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