Of Particular Significance

Category: General Relativity

Just a brief note, in a very busy period, to alert those in the Providence, RI area that I’ll be giving a colloquium talk at the Brown University Physics Department on Monday November 18th at 4pm. Such talks are open to the public, but are geared toward people who’ve had at least one full year of physics somewhere in their education. The title is “Exploring The Foundations of our Quantum Cosmos”. Here’s a summary of what I intend to talk about:

The discovery of the Higgs boson in 2012 marked a major milestone in our understanding of the universe, and a watershed for particle physics as a discipline. What’s known about particles and fields now forms a nearly complete short story, an astonishing, counterintuitive tale of relativity and quantum physics. But it sits within a larger narrative that is riddled with unanswered questions, suggesting numerous avenues of future research into the nature of spacetime and its many fields. I’ll discuss both the science and the challenges of accurately conveying its lessons to other scientists, to students, and to the wider public.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON November 15, 2024

Recently a reader, having read my post about why the speed of light seems so fast, sent me two questions that highlight important cosmic issues.

  1. Is there in fact anything within physics as it’s presently understood that indeed prevents […] there existing something other than atoms as some basic “unit”?
  2. I’ve long wondered why it is that despite the seeming brilliance of humans at building such complex understanding, we are still pushing at such limits as the time it would take to fly a space ship to another galaxy. Is it really true that nothing could ever exceed ‘c’ and thus we are indeed doomed to take lifetimes to travel beyond our solar system? Or is it because we have not yet discovered something much more fundamental about the universe, such as an ‘alternative to’ the atom?

These deep questions are examples of an even broader pair of questions about reality.

  • Which aspects of the cosmos are contingent?—in that one could easily imagine a similar universe in which these details are thoroughly altered.
  • Which aspects of the cosmos appear rock solid?—in that they are so deeply integrated into the universe that it is difficult to imagine changing them without ruining everything.
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POSTED BY Matt Strassler

ON October 28, 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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POSTED BY Matt Strassler

ON July 25, 2024

It’s always fun and interesting when a measurement of an important quantity shows a hint of something unexpected. If yesterday’s results from DESI (the Dark Energy Spectroscopic Instrument) were to hold up to scrutiny, it would be very big news. We may well find out within a year or two, when DESI’s data set triples in size.

The phrase “Dark Energy” is shorthand for “the energy-density and negative pressure of empty space”. This quantity was found to be non-zero back in 1998. But there’s been insufficient data to determine whether it has been constant over the history of the universe. Yesterday’s results from DESI suggest it might not be constant; perhaps the amount of dark energy has varied over time.

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON April 5, 2024

One of the most challenging aspects of writing a book or blog about the universe (as physicists currently understand it) is that both writer and reader must confront the concept of fields. The problem isn’t that fields are intrinsically that complicated. It’s that they are an unfamiliar abstraction — and novel abstractions of any sort are always difficult both for a writer to describe and for a reader to grasp.

What I’ll do today is give an explanation of fields that is complementary to the one that appears in the book’s chapters 13 and 14. The book’s approach is slow, methodical, and detailed, but today’s will be more of an overview, brief and relatively shallow, and presented in a different order. You will likely come away with many unanswered questions, but the book should help with that. And if the book and today’s post combined are still not enough, you can ask a question in the comments below, or on the book question page.

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POSTED BY Matt Strassler

ON March 21, 2024

Recently, a reader raised a couple of central questions about speed and relativity. Since the answers are crucial to an understanding of Einstein’s relativity in particular and of the cosmos in general, I thought I’d bring them to your attention, in case you’ve had similar questions.

The Questions

I understand that the vacuum speed of light [“c“] is constant throughout the Universe, and I’m familiar with the math that shows that the energy required to accelerate a particle becomes infinite as the speed approaches c. But what physical effect enforces this behavior? If a proton, for example, gets ejected in a supernova explosion, how does it “know” that it’s getting close to c and can’t go any faster?

And as a corollary to this question, what is the reference frame for measuring these relativistic velocities? For example, when a particle beam at CERN is said to be moving at 99.99% the speed of light, is that speed relative to the infrastructure at CERN? Or does it somehow account for the velocity components that arise from the rotation of the Earth, the orbital motion of the Earth around the Sun, the galactic motion of the Sun in the Milky Way, and so on?…

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON March 6, 2024

A lot is happening on this end. 

Carroll is a professor of theoretical physics and philosophy at Johns Hopkins University, while Whiteson is a professor of experimental particle physics — a member of the ATLAS experiment at the Large Hadron Collider — at the University of California, Irvine. Both are well-known authors and great communicators; check them out!

Stay tuned for far more book-related material; there will be a whole wing of this website devoted to answering readers’ questions and providing additional information for those who want to know more!

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON March 5, 2024

Nothing goes faster than the speed of light in empty space, also known as the cosmic speed limit c. Right? Well, umm… the devil is in the details.

Here are some of those details:

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON February 20, 2024

My two new webpages from earlier this week addressed the zero-point energy for the simple case of a ball on a spring and for the much richer case of a guitar string; the latter served as a warmup to today’s webpage, the third in this series, which explains the zero-point energy of a field of the universe. This subject will lead us head-first into the cosmological constant problem. As before, the article starts with a non-mathematical overview, and then obtains the results stated in the overview using pre-university math (except for one aside.) [As always, please comment if you spot typos or find some of the presentation especially confusing!]

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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON February 16, 2024

(This is the third post in a series, though it can be read independently; here are post #1 and post #2; and post #4 blows this one out of the water, so don’t miss it!)

Measuring the distance to the Sun is challenging, for reasons explained in my last post. Long ago, the Greek thinker Aristarchus proposed a geometric method, which involves estimating the Moon’s sunlit fraction on a certain date. Unfortunately, because the Sun is so far away, his approach isn’t powerful enough; Aristarchus himself underestimated the distance. [This last remained true for later astronomers before the 17th century, though they got closer to the truth, presumably by using more precise methods than you or I could easily apply. I doubt anyone truly found a maximum possible distance to the Sun just using geometry.] The best we can do, using Aristarchus’ method and our naked eyes, is determine a minimum possible distance to the Sun: a few million miles.

Figure 1: A simple application of Aristarchus’ method tells us that the minimum distance to the Sun is a few million miles (km), ruling out the red region. But the entire green region is still allowed.

Today we’ll see how to obtain a maximum distance to the Sun, using an approach suggested in the previous post: by measuring speeds. Specifically, we’ll make use of a speed that the ancient astronomers weren’t aware of: the speed of light, also known as the cosmic speed limit c. That’s 186,000 miles (300,000 km) per second, or 5.9 trillion miles (9.5 trillion km) per year. We’ll find the Sun’s distance is less than 12 billion miles… still much larger than its true distance, but a significant improvement on our starting point!

Figure 2: By the end of this post, we’ll know a maximum possible distance for the Sun, too.
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Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON January 19, 2024

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