Logical positivism [split: A splendid video about evolution]

I think it’s you who are misinterpreting what physics actually tells us. The mathematics behind the block universe is sound: solutions to Einstein’s field equations yield metrics in which time t is a coordinate on the same footing as x, y, z.

This is only true because physicists redefine space and time by introducing a metric which is not an identity matrix.

That befuddles many who don't know physics, and almost certainly confuses the hell out of some physicists.

My point is that it really isn't playing ball to redefine ideas that already have a meaning!

The idea of a block universe seems much less exciting when you realise that the time dimension is multiplied by sqrt(-1).

This leaves non scientists to either 'admit' that they never understood what space and time were (!!) or to just give up. On the other hand, kids learning science go away with the idea that non-scientists don't understand what space and time are.

David

This is only true because physicists redefine space and time by introducing a metric which is not an identity matrix.

That befuddles many who don't know physics, and almost certainly confuses the hell out of some physicists.

My point is that it really isn't playing ball to redefine ideas that already have a meaning!

The idea of a block universe seems much less exciting when you realise that the time dimension is multiplied by sqrt(-1).

This leaves non scientists to either 'admit' that they never understood what space and time were (!!) or to just give up. On the other hand, kids learning science go away with the idea that non-scientists don't understand what space and time are.

David

There’s nothing odd about sqrt(-1) - what would the issue be in your opinion?

There’s nothing odd about sqrt(-1) - what would the issue be in your opinion?

Well suppose you tried to rent an office for a certain chunk of time, and you specified this in terms of a 4-volume. Since you couldn't expect the clerk to know about metrics, you would specify the 4-volume as 4 metres x 4 metres x 4 metres x sqrt(-1) x q, where q could be whatever you thought appropriate.

Tell me what response you would be likely to get!

Or maybe tell me how you visualise a 4-volume.

Yet people end up talking about the block universe because physicists have fed them that concept (often without the sqrt(-1)).

David

Well suppose you tried to rent an office for a certain chunk of time, and you specified this in terms of a 4-volume. Since you couldn't expect the clerk to know about metrics, you would specify the 4-volume as 4 metres x 4 metres x 4 metres x sqrt(-1) x q, where q could be whatever you thought appropriate.

Tell me what response you would be likely to get!

Or maybe tell me how you visualise a 4-volume.

Yet people end up talking about the block universe because physicists have fed them that concept (often without the sqrt(-1)).

David

I don’t follow your argument but I accept that complex numbers are needed in some mathematical models of the world. They are all over in quantum mechanics so why not in gravity?

If your point is that physicts should be less outspoken in metaphysical debates about how much exactly we can claim to “know” I agree. As Newton wrote “What we know is a drop. What we don't know is an ocean,”

I don’t follow your argument but I accept that complex numbers are needed in some mathematical models of the world. They are all over in quantum mechanics so why not in gravity?

Well I think QM is somewhat different. The wavefunvtions can be complex, but they are not directly observable. The thing you observe iinvolves a MOD somewhere (or an equivalence such as psi multiplied by its complex conjugate. The same sort of thing is done in electric circuit theory - nothing magical at all.

However when it comes to a volume of space, that would normally be observable, but what then is the volume of a piece of block universe, which will look like somethingreal*sqrt(-1).


I mean, can you actually visualise a block of space that is complex?
quote]
If your point is that physicts should be less outspoken in metaphysical debates about how much exactly we can claim to “know” I agree. As Newton wrote “What we know is a drop. What we don't know is an ocean,”
[/quote]

My point is that mathematical models can make people think they understand something like the block universe - your whole life (say) hanging there in 4-d space-time - when really they dont.

They can also take folk ideas, and wrap them into something else.

David

My point is that mathematical models can make people think they understand something like the block universe - your whole life (say) hanging there in 4-d space-time - when really they dont.

Mathematical models are extremely poor to utterly useless substitutes for actual observations of something physical and tangible. Physics used to be about that ~ making some physical observation, and then building a mathematical model to attempt to explain it. These days, we have mathematical models first... with the observations being interpreted through the models second. Like "black holes", where we have absolutely no idea what's going on.

Same with metaphysical-level claims like "block universe" which is an absurdity that runs completely counter to even the most basic observations about how our world works in a practical, logical and intuitive sense. Believers in "block universe" certainly don't act like they're in one.

However when it comes to a volume of space, that would normally be observable, but what then is the volume of a piece of block universe, which will look like somethingreal*sqrt(-1).

I think you have misunderstood something about general relativity. In classical general relativity, the solutions to Einstein’s field equations are real, so sqrt(-1) does not appear in any observable quantity. The imaginary unit appears fundamentally when trying to combine general relativity with quantum mechanics. If you doubt me, check the Schwarzschild solution, which describes the mechanics of the solar system — no complex numbers occur.

I think you have misunderstood something about general relativity. In classical general relativity, the solutions to Einstein’s field equations are real, so sqrt(-1) does not appear in any observable quantity. The imaginary unit appears fundamentally when trying to combine general relativity with quantum mechanics. If you doubt me, check the Schwarzschild solution, which describes the mechanics of the solar system — no complex numbers occur.

Sorry for the slow response - other things distracted me!

I was talking about the Speical Relativity limit of GR where one has a choice to either put an explicit sqrt(-1) or hide it in a 'metric' that is really relevant to GR.

My point fundamentally is that the SR or GR mathematical model of space-time cannot be readily visualised, and the block universe is far more abstract than physicists pretend.

In Minkowski space you either have an explicit sqrt(-1) or a metric that serves to hide that complexity.

I don't see a good analogy with QM.

Incidentally, 4-dimensional space has actually been studied, the fourth dimension had been studied by 
Charles Howard Hinton, and is quite distinct from Minkowski space, and has no lurking sqrt(-1). Sadly it seems to be only a mathematical abstraction.

David

Sorry for the slow response - other things distracted me!

I was talking about the Speical Relativity limit of GR where one has a choice to either put an explicit sqrt(-1) or hide it in a 'metric' that is really relevant to GR.

My point fundamentally is that the SR or GR mathematical model of space-time cannot be readily visualised, and the block universe is far more abstract than physicists pretend.

In Minkowski space you either have an explicit sqrt(-1) or a metric that serves to hide that complexity.

I don't see a good analogy with QM.

Incidentally, 4-dimensional space has actually been studied, the fourth dimension had been studied by 
Charles Howard Hinton, and is quite distinct from Minkowski space, and has no lurking sqrt(-1). Sadly it seems to be only a mathematical abstraction.

David

Hi David, I’m sorry but what you are writing here is simply incorrect and sqrt(-1) does not occur in any of the theories of special or general relativity - please see https://en.m.wikipedia.org/wiki/Minkowski_space the scalefactor of t in the Minkowski metric is in fact c^2 and not sqrt(-1).
Do you have a reference to the source of your claim?