Activity – Physics Cafe

Mike Witt replied to the topic February 15th – GR Continues in the forum 2025 Relativity Series 1 day, 13 hours ago

As we get ready to look at the Equivalence Principle, a note of warning, because I think the terminology in Collier’s write-up is confusing and it starts off with a major typo.

(1) The write-up starts on page 163 (of the orange edition). There two bullet points early on. The first one says:

* The weak equivalence principle states that ……[Read more]
Mike Witt replied to the topic February 8th: General Relativity Continues in the forum 2025 Relativity Series 3 days, 3 hours ago

The little “spacetime creed” above is supposed to provide a little (humorous) commentary on the flowchart used in the meeting.
Mike Witt replied to the topic February 8th: General Relativity Continues in the forum 2025 Relativity Series 3 days, 3 hours ago
Mike Witt started the topic February 15th – GR Continues in the forum 2025 Relativity Series 3 days, 3 hours ago

Meeting link: https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1

Details TBD …

The Video will appear below a few days after the meeting:
Mike Witt started the topic February 8th: General Relativity Continues in the forum 2025 Relativity Series 1 week, 4 days ago

Meeting link: https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1

Details TBD, but we’re planning to step back, look at the big picture, and brainstorm about our study plan.
I’ll start things off with a “flowchart” (that you might have already seen).

The Video will appear below a few days after the meeting:
Mike Witt started the topic February 1st: More on vectors and one-forms in the forum 2025 Relativity Series 2 weeks, 2 days ago

Meeting link: https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1

Details TBD. I don’t know yet whether there will be a presentation or if we’ll just work together on recent topics.

The Video will appear below a few days after the meeting:
Scott Schafer replied to the topic January 25th: Tensor Homework #1 in the forum 2025 Relativity Series 2 weeks, 3 days ago

Solutions updated and corrected
Scott Schafer replied to the topic January 25th: Tensor Homework #1 in the forum 2025 Relativity Series 2 weeks, 4 days ago

I posted my solutions in the meeting above. I was not able to apply the coordinate transformation equations as expected for problems 3 and 4 and would like to review that with the group.
John Scott replied to the topic January 25th: Tensor Homework #1 in the forum 2025 Relativity Series 2 weeks, 4 days ago

Thanks; I did mean question 1, not 2.
Scott Schafer replied to the topic January 25th: Tensor Homework #1 in the forum 2025 Relativity Series 2 weeks, 5 days ago

Hi John,

1a has two upper and two lower indices, whereas 1b (phi) has no indices at all
1c is the combination of two tensors using the Einstein summation convention, yes!
John Scott replied to the topic January 25th: Tensor Homework #1 in the forum 2025 Relativity Series 3 weeks ago

Scott, on the homework:
* does question 2b show Φ with 2 superscripts?
* is question 2b asking about the tensor that results from multiplying those 2 items together?
John Scott started the topic January 25th: Tensor Homework #1 in the forum 2025 Relativity Series 3 weeks ago

Meeting link: https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1

Tensor resources:
Tensor Intro Notes
Spacetime Coords Tensors
One Form Transformation
Tensor Review Notes

Tensor homework to go over:
Tensor Problems 1
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Scott Schafer started the topic January 18th: Tensor Intro Review in the forum 2025 Relativity Series 1 month ago

Tensor Discussion

Meeting link: https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1

Tensor Intro Notes
Spacetime Coords Tensors
One Form Transformation

We’ll review some previous notes and then work out some additional transformations. After that we can begin to introduce derivatives on tensors which will pave the way…[Read more]
John Scott started the topic January 11: Proposition 6 (Finding the Centripetal Force for Any Orbit) in the forum 2025-2026 Principia Series 1 month, 1 week ago

Meeting link: https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1
John Scott started the topic Sunday Social, January 4 in the forum Announcements 1 month, 2 weeks ago

We’ll start the new year with a social hour Sunday at our regular time:
Vancouver/Oregon 3pm
Colorado 4pm

Join using https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1
For questions or comments, use https://physicscafe.org/topic/january-4th-new-year-social/

Hope to see you there.
Mike Witt started the topic January 4th New Year Social in the forum Meetings 1 month, 2 weeks ago

Details TBD. I need to figure out what link we’re using!
Mike Witt replied to the topic November 30th: Tensor Discussion in the forum 2025 Relativity Series 2 months ago

Here’s my two cents about basis vectors and their transformation.
John Scott started the topic December 14: Propositions 1 and 2 (the Area Rule) in the forum 2025-2026 Principia Series 2 months ago

I’ll cover Proposition 1, in which Newton proves Kepler’s area rule.

Meeting link: https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1
John Scott started the topic New Meeting Link in the forum Announcements 2 months, 1 week ago

Hi All,

For the foreseeable future, starting Sunday, we will use Zoom with the following new link:
https://us06web.zoom.us/j/87696074341?pwd=N17bmYVaABjibjrFsyEF3QIZB4Ds4o.1

Note this is different from the previous Zoom link because that account needs to stay private to Tina.

Reasons for dropping Google Meet:
* recording (on the free version)…[Read more]
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