22,915 reputation
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bio website lightandmatter.com
location Fullerton, California
age
visits member for 3 years, 2 months
seen 21 hours ago

I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


1d
comment Tensor equations in General Relativity
Tensorial relationships are form-invariant under a change of coordinates. In SR, a choice of coordinates can be identified with a choice of observer, but that's not the case in SR.
2d
comment When does a singularity start to exist during a black hole formation?
The "when" part of the question has no definite answer. Simultaneity isn't well defined in general relativity, and it isn't even well defined for a particular observer in a particular state of motion, as it would be in special relativity.
2d
comment When does a singularity start to exist during a black hole formation?
It is the existence of the even horizon that defines the black hole "singularity". No, the event horizon and the singularity are two different things.
2d
comment When does a singularity start to exist during a black hole formation?
I understand that general relativity fails to describe the interior of a black hole Not true. It only fails to describe the singularity.
2d
awarded  Nice Answer
Sep
26
awarded  Enlightened
Sep
26
awarded  Nice Answer
Sep
26
comment Does space expand locally without restriction in freefall to central region of black hole?
Well, it isn't right under GR. No, it simply isn't right. That is, you're throwing around words without knowing what they mean.
Sep
26
comment Does space expand locally without restriction in freefall to central region of black hole?
At some point the velocity based local space expansion (special relativity) will be overtaken by gravitational space expansion (general relativity), Huh? This isn't right.
Sep
26
comment Spacetime - Fact, Hypothesis, or Working Model?
@Danu: In everyday life, there are few implications (which explains why it took until 1905 to discover SRT) Not true! A magnet sticks to your fridge because of relativity. GPS wouldn't work without relativity. The night sky is black because of relativity.
Sep
26
comment Spacetime - Fact, Hypothesis, or Working Model?
The title makes it sound like the question is about a specific concept, which is spacetime. The question itself makes it sound like it's a much more general question about the empirical status of special relativity. Which is it? If it's the latter, then I think the question is too broad.
Sep
26
comment How strong is the force of space expansion?
The calculation you're trying to do is done in this answer: physics.stackexchange.com/a/70056/4552
Sep
26
answered Can gravitational waves be red-shifted?
Sep
24
comment What is the math knowledge necessary for starting Quantum Mechanics?
There are many different mathematical levels at which one can learn quantum mechanics. You can learn quantum mechanics with nothing more than junior high school algebra; you just won't be learning it at the same level of mathematical depth and sophistication.
Sep
24
awarded  Autobiographer
Sep
24
comment How did Newton discover his second law?
This doesn't answer the question.
Sep
24
answered Experiment which shows that Newtons third law is not true for magnetic forces
Sep
24
comment Why is the focal length of a convex mirror negative?
I've heard of the American and European sign conventions, but not the Cartesian one. I wonder if there is a description somewhere of the various systems, side by side.
Sep
23
awarded  Necromancer
Sep
23
comment Is mass in particle physics classical or relativistic?
There are two conventions for how to define mass in relativity: physics.stackexchange.com/questions/133376/… . Which one do you have in mind, the obsolete one or the modern one? Using the modern definition, the mass of a material object is exactly the same as the Newtonian mass.