Oh no... I don't really understand Symmetry!

[iantaylor2uk]

18 hours ago, vlaiv said:

Not sure that physical law being the same constitutes symmetry.

Time has two symmetries - time reversal and time shift symmetry.

First one states that physical laws are equally applicable if you turn the arrow of time. If instead of going forward - time is taken to flow backward - laws would still hold the same. Shape / form of physics laws does not change at all.

Crude representation of this would be the fact that ball follows parabola trajectory no matter if time moves forward or backward. Take movie of flying ball and play it backwards - trajectory will "look right" regardless of the fact that time is flowing backward.

Similarly - if you take a sped up video of planets orbiting the star - there is no way of telling if that movie is played forward or backward.

Our physical laws (mostly) follow this symmetry down to particle level - or should we say that what we see stems from universe behaving in that way on particle level.

However - that symmetry is "broken" or T symmetry does not stand, here is interesting (and light weight) article on the subject:

https://bigthink.com/starts-with-a-bang/laws-physics-not-time-symmetric/

Then there is time shift symmetry - which states that result of experiment should be the same if one performs it "in the evening" or "in the morning". Time T0 is just arbitrary moment and as such does not influence result of physics experiment (again, laws do not change).

This is also not the case. In general relativity where time is tied in with space in space-time - it can bend and flow differently and it does matter at what time you perform the experiment as time is no longer linear and omnipresent / universal.

Just to be clear - the form that physical laws take are constrained by symmetry. To be specific, the Lagrangian proposed for a physical law (such as electromagnetism, or the strong force, or even gravity) has to be invariant under local symmetries - the ones covered by Noether's theorem are examples of these. Most physical laws have coupling constants, and I guess these could potentially change without changing the underlying symmetries of the forces, but you would have to have observational data for this, and research aimed at seeing if the fine structure has changed with time have not, to my knowledge, found much, if any change. 

I am not an expert on general relativity, but claims that energy is not conserved assume that space-time does not have energy associated with it. For example, if photons from the early universe are red-shifted, then their energy is less, and so you could ask where the energy has gone to. If you don't think it has gone anywhere you would claim that energy is not conserved. However, I would have thought it to be a reasonable assumption is that the energy goes into the work done for space-time to expand. We don't yet have a viable theory of space-time at the microscopic level, although we do know that space-time has entropy (see very recent paper at: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.221501 and also available at: https://arxiv.org/abs/2212.10607), so it would be reasonable to assume it would have other thermodynamic properties such as energy

[Macavity]

Quote

@AstroKeith ... and then there is 'Super-symmetry' !

And, thanks to a FEW* folks chosing, wisely or unwisely, to do "String Theory"...
the WORLD "hates" Physicists? An idea proposed by a Youtube Astrophysicist! 😛
* Apparently, more than a few did, but absolutely nothing to do with me! lol

Edited July 9, 2023 by Macavity

[SwiMatt]

On 08/07/2023 at 15:29, iantaylor2uk said:

I don't think it matters that the universe is not symmetric. What is being claimed is that physical laws should be the same an hour from now, or a thousand years in the future (or past) or a billion years in the future or past. Of course this is an assumption. If there is evidence that physical laws were different 10 billion years ago we would have to rethink things.

As an aside, we rarely think about how all of modern physics is resting on the Cosmological Principle (the assertion that on large scales the universe "looks the same" for all observers - and thus the laws of physics also look the same for all observers). I can absolutely imagine the universe showing different laws of physics - or different facets of the same law that we are yet to understand - to different observers, which would lead to interesting theoretical discourse. Of course, pragmatically, the principle is a very fair assumption, but one has to wonder 😄

 

On 09/07/2023 at 14:32, Macavity said:

And, thanks to a FEW* folks chosing, wisely or unwisely, to do "String Theory"...
the WORLD "hates" Physicists? An idea proposed by a Youtube Astrophysicist! 😛
* Apparently, more than a few did, but absolutely nothing to do with me! lol

Not sure where the idea that the world "hates" physicists comes from... they are the category of scientists that is most respected in the world - not always based on real merit 😂 can I ask what youtube astrophysicist came up with that? (I have a guess, I wanna see if I'm right)

Edited July 14, 2023 by SwiMatt

[Macavity]

On 14/07/2023 at 08:55, SwiMatt said:

Not sure where the idea that the world "hates" physicists comes from... they are the category of scientists that is most respected in the world - not always based on real merit 😂 can I ask what youtube astrophysicist came up with that? (I have a guess, I wanna see if I'm right)

Hey, I like a good RANT, by some people - Perhaps not everyone? lol
I now sense, whatever one says, Science Fans will "run with the ball"? 😛

Edited July 21, 2023 by Macavity

[saac]

A few observations on the so called "communicator"  in the youtube video:

How can a theory lie?   As for communication, you would serve your audience better by giving them your undivided attention - ditch the "down with the kids playing a computer game", it doesn't translate.   In simple terms poor manners, and yes these still count. 

Ok rant over.  What I would like to know is, who appointed these "science communicators" and why are they trying to convince us that the "public" had any interest whatsoever in a theory they could not understand, never mind physics/science? Get a proper job, become an influencer 😁

Jim

Edited July 21, 2023 by saac

[Macavity]

7 hours ago, saac said:

As for communication, you would serve your audience better by giving them your undivided attention - ditch the "down with the kids playing a computer game", it doesn't translate.   In simple terms poor manners, and yes these still count.

😛 Sometimes ya don't know whether to laugh or cry? Playing a computer game, while
you address your audience? Is this some kind of... Dada-esque experience? Recent years
have left some of us removed from the NORMAL world? But I'm not entirely guileless! 🤣

Sometimes entertainers (even Pop Scientists) "push" things? How far can I disrespect my
audience, while still retaining undying loyalty... "I'm in with the in-crowd"? (Brian Ferry) 😛

Lew Kowarski (First CERN director) wrote: "A genuine scientist is eager to establish his
reputation amongst those who know his subject;  A mystagogue builds his among those
who do not". Apparently a ref. to G.K.Chesterton: "But the mystagogue hides a thing
in darkness and when you find it, it's a platitude". (The incredulity of Father Brown).

Nothing like a good "Quote" - Appear intellectual... Disarm critics? 😁
 

Edited July 22, 2023 by Macavity

[saac]

5 hours ago, Macavity said:

Lew Kowarski (First CERN director) wrote: "A genuine scientist is eager to establish his
reputation amongst those who know his subject;  A mystagogue builds his among those
who do not". Apparently a ref. to G.K.Chesterton: "But the mystagogue hides a thing
in darkness and when you find it, it's a platitude". (The incredulity of Father Brown).

Nothing like a good "Quote" - Appear intellectual... Disarm critics? 😁
 

I like that.  Seems to me that the internet is a breeding ground for science mystagogues all chasing their 15 minutes of fame. 

I used to think the internet was a great democratiser of knowledge with its easy access to publication (I still do really). However, there is definitely an inverse relationship between the ease of publication and the usefulness of the message. Maybe some knowledge should remain hard won. 

Jim 

Edited July 22, 2023 by saac

[Macavity]

On 22/07/2023 at 12:29, saac said:

I used to think the internet was a great democratiser of knowledge...

 I have to be careful... but at this point a "smart cookie" jumps up and says:
"Science is not a Democracy"! Especially if they think Voting is a tad passe? 😛
(As one scientist said: "Science doesn't need to Vote re. Water being Wet"!)

Maybe it highlights difference between Scientific & Public (even science fan!)
understanding of scientific concencesus - reasonable Faith, in Peer review? 😉

I cherish my copy of Kowarski's Book. If you are (very) interested in the early
history of "Big Science" - You may still find one? He has a whole section on
"Pathologies of Science". (ALL these were known - Even back in the 50s/60s!)
Maybe, we should all go and see "Oppenheimer" or something. 😛

Edited July 23, 2023 by Macavity

[andrew s]

Sadly fraud is not unkown in science especially now the competition for fund makes verifying results unattractive to competing groups. Micro biology has had it's fair share of issues this for example is an interesting read. 

Regards Andrew 

[Macavity]

Well, the "Pathologies" discussed were: Fuhrerism, Too much heirarchy, Too little overlapping,
"Happy Sleep", Commanders versus Creators, Brilliant Individualists, Academism, Cliques,
Empire Builders (and our friends, the Mystagogues!) - Physics is always HONEST (guv)! 😉

The problem with (experimental) "Big Science" is scalabilty? Being "One in n-thousand"? Just reading
the "laments" of a young scientist - His experience was good training re. a host of transferable skills,
but he never got to personally push back the "Frontiers of Science"? A Musician, lamenting his own
mediocrity? I really do wonder if this is part of the (internet era) expectations, being "famous for..."?
Lets hope feelings of "pointlessness" don't spread to the Field of Amateur Astronomy? 😅