That's an interesting association with position sensors, benb.
For my part, I'm happy to leave the geeky LIGO stuff to the boffins!
Given the large number of noise sources (e.g. quantum, thermal, seismic & Newtonian gravitational) it's a marvel they can detect gravity wave signals.
The trick is the noise is not correlated between the sensors but the gravity waves are correlated. if you have multiple sensors, that allows you to extract information at/below the noise floor which in broad terms is what’s happening with LIGO. This is engineering physics at its very best - achieving the seemingly impossible.
Its a bit of a rambling podcast and Lex Fridman touches on multiple subjects and I've gotten about halfway through. Fridman takes a bit of a good-humoured dig at TP's in general. I like Sean Carroll because he's the least of the snake oil TP's out there and doesn't try to sell stuff (from my limited exposure to his writing, YouTube videos etc). He's quite honest in the podcast about starting to write papers and then realising they were b.s. so dropping them. As usual, Fridman asks him about aliens. Carroll does not believe the cosmos is crawling with advanced civilisations, so I immediately rank him 9/10 as a credible, thoughtful, individual. They talk about time (one of my favourite subjects, as you know and like to take a dig at me about Galu). He recounts how Einstein thought it was an illusion (despite the fact that it is quite malleable and changes with relative velocity and in a gravitational field), Newton's view (it is the same everywhere) and Carroll's view ('it just, you know ticks by on your watch wherever you are'). For that, I deduct 2 points off the TP credibility index, and Carroll is now rated at 7/10, which on the Bonsai scale is quite an honour I have to tell you
I inevitably finished the Lex Fridman/Sean Carroll dialogue, which works well just on sound as a podcast. I am not a lazy student.
Dear old dead-eyed Lex inevitably diverted it to AI, TLM (Think Computer Intelligence) and Consciousness, and Sean kept up with him though I could see he was being polite. Really it would better employ Sean to talk on Pure Physics like Special and General Relativity IMO...
I found Sean's notion of curved paths in the Time component as well as the Space component interesting.
I think Sean Carroll's "Mindscape" may be more fruitful for us ideas people.
Couldn't resist listening to another physics populariser, Prof. Lisa Randall on Dark Matter and Dark Energy. Very good, aside more Lex Fridman hobbyhorses again.
Further discoveries about the Nova, T CrB. Time is tight after initial detection for full brightness near magnitude 2.5:
Fades a bit even in 12 hours, but the window is about a week sometime in the next few months:
https://www.creators.com/read/stargazers/04/24/coming-soon-to-a-sky-near-you-a-new-star
I expect I shall be the main man here on this, I am watching the skies! Galu , and there is no nice way to say this, will doubtless claim it is too cold to go outside or some other excuse...
Dear old dead-eyed Lex inevitably diverted it to AI, TLM (Think Computer Intelligence) and Consciousness, and Sean kept up with him though I could see he was being polite. Really it would better employ Sean to talk on Pure Physics like Special and General Relativity IMO...
I found Sean's notion of curved paths in the Time component as well as the Space component interesting.
I think Sean Carroll's "Mindscape" may be more fruitful for us ideas people.
Couldn't resist listening to another physics populariser, Prof. Lisa Randall on Dark Matter and Dark Energy. Very good, aside more Lex Fridman hobbyhorses again.
Further discoveries about the Nova, T CrB. Time is tight after initial detection for full brightness near magnitude 2.5:
Fades a bit even in 12 hours, but the window is about a week sometime in the next few months:
https://www.creators.com/read/stargazers/04/24/coming-soon-to-a-sky-near-you-a-new-star
I expect I shall be the main man here on this, I am watching the skies! Galu , and there is no nice way to say this, will doubtless claim it is too cold to go outside or some other excuse...
I should like to learn more about the distinction between time curvature and space curvature.
If only I knew at what time in the 2 hr 35 min video that discussion commences!
Galu , and there is no nice way to say this, will doubtless claim it is too cold to go outside or some other excuse...
On the contrary, I am going to camp out in the garden every night from now till September if necessary in order to be one of the first to witness T Coronae Borealis become visible to the naked eye.
Overnight temperatures here are currently dropping to -2 °C, but they could get above freezing by July!
Look for the Northern Crown? All I can say is, "Wear the fox hat"!
Ignore gravity for s second and let’s consider a flat 2 dimensional plane.
If I were to warp time ie create a time gradient between a number of points on the flat plan, I’d guess the behaviour of an object encountering such a time gradient would be indistinguishable from that same object encountering a similarly shaped gravity field (I’m thinking here about Einstein’s duality principle).
Really, Bonsai (Or Andrew as I prefer to call you, Galu being Jock AFAIK..), I don't have much time for String Theory, pretty though the Ed Witten maths is. "Not Even Wrong" as Peter Woit rants!
And it is a distraction here, IMO. Though Lisa Randall believes that an incredibly extended or essentially stretched hidden dimension might get some mileage too... Who knows?
No. FWIW, all the good stuff in your Lex Fridman link is in the first 22 minutes. After that Lex, as usual, wants to talk about Aliens, AI and consciousness.... YUK, don't watch!
@Galu. About 12 minutes in Sean Carroll makes the strangest remark that the duration in Time for a geodesic (Shortest Path) in Space is the LONGEST possible time. Something inverse about time's relationship to space that is implied in the negative sign in Einstein's conserved distance between two events in spacetime for all observers. s^2 = dx^2 + dy^2 + dy^2 - c^2 x dt^2 with d representing Delta an' all that. I need to mull that over in terms of the Twins Paradox and such. Also in terms of photon orbits round a Black Hole, which is essentially a circle, of course.
Podcast by Sean on his most recent book, which I have read: The Biggest Ideas in the Universe, Space, Time and Motion.:
https://www.preposterousuniverse.com/podcast/2022/09/19/211-solo-secrets-of-einsteins-equation/
This is good. I have heard it before.
Best, Steve.
And it is a distraction here, IMO. Though Lisa Randall believes that an incredibly extended or essentially stretched hidden dimension might get some mileage too... Who knows?
No. FWIW, all the good stuff in your Lex Fridman link is in the first 22 minutes. After that Lex, as usual, wants to talk about Aliens, AI and consciousness.... YUK, don't watch!
@Galu. About 12 minutes in Sean Carroll makes the strangest remark that the duration in Time for a geodesic (Shortest Path) in Space is the LONGEST possible time. Something inverse about time's relationship to space that is implied in the negative sign in Einstein's conserved distance between two events in spacetime for all observers. s^2 = dx^2 + dy^2 + dy^2 - c^2 x dt^2 with d representing Delta an' all that. I need to mull that over in terms of the Twins Paradox and such. Also in terms of photon orbits round a Black Hole, which is essentially a circle, of course.
Podcast by Sean on his most recent book, which I have read: The Biggest Ideas in the Universe, Space, Time and Motion.:
https://www.preposterousuniverse.com/podcast/2022/09/19/211-solo-secrets-of-einsteins-equation/
This is good. I have heard it before.
Best, Steve.
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@Bonsai Re the distinction between time curvature and space curvature:
General relativity tells us that four-dimensional spacetime is distorted in the presence of matter. Obviously this distortion results in a curvature not only of each of the three dimensions of space but also of the single dimension of time.
Objects which move through spacetime much slower than the speed of light will travel much farther in time than in space and consequently are mainly subject to time curvature.
According to Einstein, your weight on Earth can be taken to be the result of time curvature only because you are not moving much in the space component of spacetime.
General relativity tells us that four-dimensional spacetime is distorted in the presence of matter. Obviously this distortion results in a curvature not only of each of the three dimensions of space but also of the single dimension of time.
Objects which move through spacetime much slower than the speed of light will travel much farther in time than in space and consequently are mainly subject to time curvature.
According to Einstein, your weight on Earth can be taken to be the result of time curvature only because you are not moving much in the space component of spacetime.
To be picky, a geodesic is the shortest path between two points in spacetime, not in space.
The orbit of the Earth may be represented by a geodesic.
Could the "longest possible time" be related to the motion of the Earth in spacetime?
The Earth's Worldline resembles a helix whose width in space is only one astronomical unit, but whose length in the time direction is measured in lightyears!
Does 👆 address that if an object were to encounter a time gradient it would behave exactly as if it were encountering a gravity gradient? Assume flat or curved.
Seems to me that Ed Witten is quite honest about ST in the interview. He states it provided an answer for almost everything in the quantum field, and gravity emerges from the theory BUT it is not able to unite QFT and gravity. He also says ST research has provided a rich suite of mathematical tools that may be able to be applied to other areas of research.
I wasn't attempting to address the contents of your post #3,992. Were you comparing time gradient dependent gravity with Newtonian gravity?
I am having enough trouble contemplating the curved, four-dimensional mathematical structure called spacetime.
I'm not up on the required differential geometry, but I read that the gradient of curved spacetime includes a time derivative, whatever that means!