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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« Last post by varsigma on Today at 02:07:24 »

All that said, yes, different definitions are used, and it is commonplace to express motion through spacetime as taking place at c, expressed as a four-velocity, not a normal velocity.

I'm trying to figure out a response to the phrase "normal velocity"; if you mean the Euclidean part of the spacetime metric, I guess. But in the case of non-Euclidean solutions, I don't know what to say about it.

If you accept that "normal" is restricted to a locally defined region of the universe, the only thing moving at c is light, and the universal expansion is effectively zero; I would say that then, the universe is indeed "normal". But I know enough about the equations that I can say, that is a trivial solution.

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Chemistry / Re: Shrink ray or growth ray, how could they work?

« Last post by Eternal Student on Today at 01:30:55 »

Hi.

We can use QM equations and just plug in different mass and charge and magnetic properties....

   Yes, I suppose you could just change the physical parameters of space around the person.     Alter the constants like ε₀, the permittivity of space.   Try and do this in a small bubble around the person you're shrinking.   Very roughly it ought to affect all atoms in a similar way.

    The Bohr radius is 

     Increase and decrease ε  and atoms get bigger and smaller.

   So they can eat food and breathe the air around them because anything close to them is affected the same way.   They also don't fall through the floor by being over-dense because the floor becomes affected when their feet are on it.

One way I thought it might be possible would be y changing the mass of the involved particles.

   Actually, you only have to change the effective mass of the electrons and that's not impossible.

Precedent:
    Semiconductor theory.   The extra electron from a donor impurity atom behaves as if that electron is spread out over many hundreds or thousands of atoms in the lattice.   This can be well modelled with the usual QM model of a Hydrogen atom  where ε₀ is replaced by the appropriate ε of the bulk lattice (and the mass of the electron is usually also replaced with the effective mass of the electron in that bulk lattice).

How would you do this?
    That's a practical problem not a theory problem, so.... someone else's problem.   If you were attempting anything like the same idea as we use in semiconductor theory, then you'd actually want to put something extra into the person.   Some small particles that will act like a lattice while all the other atoms the person is made of behave like impurities in that lattice.

Best Wishes.

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Physics, Astronomy & Cosmology / Re: Will AI really replace supercomputers for weather-forecasting?

« Last post by Petrochemicals on Yesterday at 22:36:49 »

I do not see how AI can do without a super computer, AI at the minute is a targeted learning programme (narrow ai) that would only develop the same methods as existing programmes I should think, we cannot think of any other way of forecasting the weather so any narrow AI programme I should think will be along similar  requiring models of intricacy at vast scales. Maybe it could do it more efficiently, be more vigilant have more imagination and detail and become more accurate but I think it would still need the super computer models. If general ai could come up with another method rather than the 'model' method then we could get rid of the super computer. But we do not have general AI yet.

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« Last post by Eternal Student on Yesterday at 22:30:06 »

Hi.

   I said I would look into the writing by Penrose.   Sorry, that's not going to happen for a while.   We have severe weather warnings where I am.   I won't be getting to a library for a few days.
   If anyone has an online reference I'll check that  (if the phone and internet lines stay up).

Best Wishes.

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Physics, Astronomy & Cosmology / Will AI really replace supercomputers for weather-forecasting?

« Last post by evan_au on Yesterday at 21:43:30 »

On today's podcast, an interview with researchers from Google DeepMind reported results of an AI doing Medium-Range weather forecasting (up to 2 weeks in advance).
- They reported huge reductions in energy consumption, number of CPUs and computation time when using a Google TPU (AI chip) compared to thousands of CPUs in a conventional supercomputer.
- Suggesting that weather forecasting would no longer need supercomputers
- The Google chip started with the current state of the world's weather as input.

5 years ago, I listened to this interview with the European Medium-Range Weather Forecasting team.
- My vague recollection was that something like 60% of their Supercomputer usage was to produce a definition of the current state of the weather, and only 40% was predicting the future of the weather, out to 2 weeks
- There are many different sources of data on the current weather, and they don't always agree
- The data collection points are closer together over land than over sea or deserts
- And so it takes a huge amount of supercomputer analysis to integrate them all to define the current global weather

So while AI might will be able to reduce supercomputer usage by 40% for weather prediction, there is still significant research if forecasters are to reduce the other 60% of supercomputer usage.

https://omegataupodcast.net/326-weather-forecasting-at-the-ecmwf/

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Question of the Week / Re: QotW - 24.12.12 - Is there any way to harness nuclear energy other than steam?

« Last post by SeanB on Yesterday at 21:03:07 »

The one that has the longest life is to use beta emitters and a tiny capsule, isolated in a vacuum, that relies on the beta particles, which are electrons, to provide a very tiny current to power ultra low power equipment Think of things like low power clocks that run on nanowatts of power when the equipment is shut down, and also powering static memory that stores data and configuration. Expensive, only made by a few niche manufacturers, and with ITAR regulations associated with the export of them.

https://en.wikipedia.org/wiki/Betavoltaic_device

For more information.

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Question of the Week / Re: QotW - 24.12.12 - Is there any way to harness nuclear energy other than steam?

« Last post by paul cotter on Yesterday at 20:41:58 »

20% would be quite good. I'm not up to date on these developments.

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Just Chat! / Re: Is there a universal moral standard?

« Last post by alancalverd on Yesterday at 20:36:22 »

So two moral acts can be diametrically opposed. I think you have confused morality (how we should behave towards others) with a survival instinct (how we are forced to behave by circumstance). 

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New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« Last post by alancalverd on Yesterday at 20:23:35 »

Electrons are created by pair production or beta decay, so some, at least, have a birthday, and my detector says they don't all arrive together, so I can create an age gap by sending some around a magnetic loop

.

Yes, but we know what to look for. We construct the history--see Hawking and Penrose.

What we know is that if two 511 keV photons are detected simultaneously (OK, within femtoseconds, for the pedants among us!) in opposed detectors, they originated from a positron annihilation at point on the line connecting them. That is, we know their history (because there is no other possibility)  and (eventually) that tells us where the positron source is.

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Question of the Week / Re: QotW - 24.12.12 - Is there any way to harness nuclear energy other than steam?

« Last post by alancalverd on Yesterday at 20:12:35 »

There are already some promising semiconductor thermocouples with > 20% efficiency, apparently.