1

Physics, Astronomy & Cosmology / Re: Can we ever truly describe space as empty?

« on: 29/10/2021 06:47:51 »

In Einsteins universe there is no outside. The definition is one of four parameters. length, width, height, time. So you need all four for this universe to exist. Without them there is nothing. No fields, no densities and stuff and no time.

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Physics, Astronomy & Cosmology / Re: Why does double the velocity double the momentum and quadruple the KE?

« on: 29/09/2021 23:32:59 »

That one was very nice JT, intuitive. But what I don't find equivalent are the initial conditions. In the first case both kinetic energy and momentum differs from the other.

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Physics, Astronomy & Cosmology / Re: Why does double the velocity double the momentum and quadruple the KE?

« on: 29/09/2021 23:06:07 »

You're thinking of inelastic collisions relative elastic, if I get you right JT?
But that's not what I got stuck on :)

Practically it may come out that way, but using definitions as kinetic energy and momentum I don't find those two situations equivalent, and that's my headache.

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Physics, Astronomy & Cosmology / Re: Why does double the velocity double the momentum and quadruple the KE?

« on: 29/09/2021 21:48:05 »

I will need to ponder that one.
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Not here though. It will take too much place.

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Physics, Astronomy & Cosmology / Re: Why does double the velocity double the momentum and quadruple the KE?

« on: 29/09/2021 21:42:23 »

And how do would I get to a kinetic energy without a momentum involved BC?

Hmm, okay, depends on definitions. https://www.sarthaks.com/454279/a-can-kinetic-energy-of-a-system-be-changed-without-changing-its-momentum

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Physics, Astronomy & Cosmology / Re: Why does double the velocity double the momentum and quadruple the KE?

« on: 29/09/2021 21:41:00 »

How can that be BC?
What about the momentum?

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Physics, Astronomy & Cosmology / Re: Why does double the velocity double the momentum and quadruple the KE?

« on: 29/09/2021 21:12:26 »

Heh, missed the second page. It seems that you do? Assume that the the momentum of something isn't there if it is of a speed, equal to what it collides with?

Is that correct?
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Both cars use earth as their relative frame of no motion. and both cars are moving at a same speed relative earth. You put up a rock in front of any of those cars and the kinetic energy will exist, being the same for both occasions, assuming the cars to be identical clones :) as well as the speed etc.

So that kinetic energy must exist as a momentum for both cars and will transform into kinetic energy at a collision. So it should be the same as if you collide with that rock at a hundred, or crash head-on, doing fifty, into that other car, it too doing fifty although in the opposite direction.

But it is weird, momentum and kinetic energy. You could define something else than earth as your 'stationary point', some patch of space that earth swish by in its 'relative motion' through the universe. At least in relativistic terms. Then vectors and speeds relative that motion will come in and play a role for how that collision will be interpreted etc. But it won't change the kinetic energy involved in the 'system' colliding. So suddenly it's not relative anymore, or is it?

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Physics, Astronomy & Cosmology / Re: Why does double the velocity double the momentum and quadruple the KE?

« on: 29/09/2021 20:49:16 »

I not entierly sure Mr cat but it seems the culprit is in this " Why is it that if a car doing 100K crashes into a stationary car, it's a gonner, and yet if I have a head-on with another car doing 50 each, I would expect to walk away, unscathed, in my big car "

It depends on how one read it possibly but are you assuming that there is a difference between those two scenarios, in the kinetic energy experienced by the driver? As if one could assume one of those cars, regardless of which one you choose, as representing something unmovable, as a rock? In which case the ´kinetic energy' experienced then will be 'halved', represented by just one side, no matter which side you choose?

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Physics, Astronomy & Cosmology / Re: Do quantum computers imply a many-worlds interpretation?

« on: 12/09/2021 11:22:14 »

And no, quantum computing relies of superpositions, entanglements and in some motto the use of spin.  And then there is those 'probability amplitudes' and interference. It doesn't discuss what happens to those 'unused' outcomes that might had been. Maybe this is closer to what you thought of Halc?

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Physics, Astronomy & Cosmology / Re: Do quantum computers imply a many-worlds interpretation?

« on: 12/09/2021 11:10:40 »

Now you got me confused Halc?

https://plato.stanford.edu/entries/qm-manyworlds/

" The Many-Worlds Interpretation (MWI) of quantum mechanics holds that there are many worlds which exist in parallel at the same space and time as our own. The existence of the other worlds makes it possible to remove randomness and action at a distance from quantum theory and thus from all physics. "

the point is that you can't avoid them as I understands it, if you want it to hold.

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Physics, Astronomy & Cosmology / Re: Lagrangian Mechanics - Why is Nature lazy?

« on: 06/09/2021 15:22:31 »

It made me think of two things ES. Conservation of energy and the 'reason' given to how a ray choose the best path meeting a water surface. And when I think of conservation of energy I really think it 'conserves' it, any action defined..

https://en.wikipedia.org/wiki/Fermat%27s_principle
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Thinking of it, it always struck me as strange that transformations doesn't 'cost'. As far as I've seen that's the whole idea of conservation of energy when describing a 'isolated system' transforming. But to me something should be lost in each step, the end result becoming heat. If it transforms something must change. The only definition I know of there is 'useful energy' relative 'non useful energy'. JP (physicist) called it a 'coin of exchange', energy, and that one stuck in my head.

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Just Chat! / Re: Quality of discussions

« on: 25/08/2021 15:50:32 »

I think I will agree with BC. Let people do what they do, and let BC, and me, do what we does :)  It keeps it alive. TNS used to be even more lively, having a lot of spirited and knowledgeable persons in the beginning, but people dropped off by different reasons. It depends also on the direction of the site, from being something of a 'free for all', to then changing into a site primary meant for answering questions. It killed it somewhat in my opinion. No slight meant for the guys and gals longstanding here, trying for those sensible answers. It's still one of my absolute favorites.

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Physics, Astronomy & Cosmology / Re: What will be the next emerging space technology?

« on: 12/08/2021 07:09:59 »

Yeah, I agree, miniaturization will be the next field of study for space explorations.

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Physics, Astronomy & Cosmology / Re: Is "Space" distinct from "nothingness"? (and the Vacuum)

« on: 08/08/2021 21:54:38 »

No Es, that's not true. 'A (differentiable) manifold' is quite interesting but also rather hard to melt for those of us not used to to the nomenclature :)   I'm checking it out for the moment and I think it would be nice with a overview, maybe in another thread as this ones origin is quite old, just as you say.

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

as far as I'm concerned that is. Mathematics is what relativity builds on. Also, I'm afraid that it actually was me that Geordief answered to, although, I can't help finding it quite complimentary suggesting it was Collins :)

don't hesitate in using mathematics ES, just break it down for us if it gets too esoteric.

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New Theories / Re: An essay in futility, too long to read :)

« on: 22/07/2021 11:31:28 »

Your smartphone

" I found the child, a girl caked in dirt with an ailing newborn strapped to her back, hacking at the ground for cobalt at Lake Malo, not far from Kolwezi. Her limbs were like sticks, her face was crusted with mucus and she had a rib-cracking cough. The horror of her wretched existence could never be remedied by an academic report, I decided. An attempt had to be made to hold someone accountable.

I returned home and tracked down Terrence Collingsworth, a human rights lawyer and expert in strategic litigation. Together with my Congolese colleague, Roger-Claude Liwanga, a professor at Emory University, we coordinated with partners in DRC to approach families deep in the cobalt territory. We finally found 14 families who wanted to tell their stories. By September 2019, Terrence, Roger, and I were sitting down in DRC to meet Bisette.

On Monday, Bisette and 13 other families have launched a landmark legal case in DC Federal Court in the United States against Apple, Microsoft, Dell, Google and Tesla for what they consider to be the companies’ complicity in the injuries and deaths of their children. In documents filed with the court, the plaintiffs claim that the defendants are liable for forced labour under US federal law, which they allege took place at some of the biggest industrial cobalt sites in the Congo – Mashamba East, Lake Malo B-5, Commus and Tilwizembe. I am acting as an expert witness in the case. "

https://www.theguardian.com/global-development/commentisfree/2019/dec/16/i-saw-the-unbearable-grief-inflicted-on-families-by-cobalt-mining-i-pray-for-change

And those supporting it, amongst them the EU and the UK

https://www.theguardian.com/global-development/commentisfree/2021/jul/21/the-uk-has-been-linked-to-congos-conflict-minerals-where-are-the-criminal-charges

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Physics, Astronomy & Cosmology / Re: Is space in, beyond and around the universe?

« on: 01/07/2021 20:51:20 »

This will have to be a guess, but no, not as I know. A inflation, later called expansion only differs in that a inflation is assumed to go 'FTL'. And the reason why it might be able to do such a thing is that it's not mass we're talking about, it's space. Mass can't, as far the mathematics goes, but space?

The expansion also can be thought of as going 'FTL' if you look far enough out in the universe. The further away the more 'new space' can be created, and every little patch adds up to expand the distance between you and that star. and so also the 'speed' of their recession, receding relative yourself.

and most everything is made of 'space', even mass.

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Physics, Astronomy & Cosmology / Re: Does the cosmological principle dictate isotropy?

« on: 29/06/2021 15:28:44 »

I guess that's up to the definitions and scale you use Chiral. But it is still more homogeneous and isotropic than the opposite, well, as far as I know. If it wasn't one could get preferred directions in space, and relativity too should be able to be questioned, I think?

https://physics.stackexchange.com/questions/24881/what-is-meant-when-it-is-said-that-the-universe-is-homogeneous-and-isotropic
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It gets confusing very quickly if you look at mathematical models. They can allow all sorts of things if I remember right, as a 'rotating universe', or as the link refers to, as something not being isotropic still obeying GR.  http://www.scholarpedia.org/article/Bianchi_universes

Or             https://physics.stackexchange.com/questions/1048/what-if-the-universe-is-rotating-as-a-whole

But if it would rotate, wouldn't it have a preferred direction too?

"  It would be a weird place. Being non-isotropic would mean there is a preferred direction in space, for example, if the entire universe were rotating. Then the axis of rotation is a special direction. You would then see Coriolis- and Centrifugal-like effects, and the motions of planets might not even obey Newton’s laws.

Strictly speaking, it IS non-homogeneous already so that is less of an issue. Homogeneity is only an approximation that applies on a very large scale. It would be weirder if the universe actually were perfectly homogeneous as it would then be a uniform gas — no planets, no stars, no galaxies, no nothing. "  by Paul Camp, Ph. D. in theoretical physics and 30 years experience

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Physics, Astronomy & Cosmology / Re: Does the cosmological principle dictate isotropy?

« on: 28/06/2021 08:35:33 »

Myself I think it's a sane approach to the universe. Assuming that what you find here should be applicable on 'there' too. That is what we do with constants, and with conservation laws too. Then you have relative motion that 'moves us' through the universe, well presumably, and everything seems to work the same way as always when it comes to experiments and physics. Assuming the opposite moves us to something that we don't know, where whatever physics we find here being a local expression, on a 'global scale'.
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As for the scale the homogeneity in the link I gave first, relating to relativity, was defined this way

" To say the Universe is homogeneous means that any measurable property of the Universe is the same everywhere. This is only approximately true, but it appears to be an excellent approximation when one averages over large regions. Since the age of the Universe is one of the measurable quantities, the homogeneity of the Universe must be defined on a surface of constant proper time since the Big Bang. Time dilation causes the proper time measured by an observer to depend on the velocity of the observer, so we specify that the time variable t in the Hubble law is the proper time since the Big Bang for comoving observers"

And in this     https://assets.cambridge.org/97805218/47049/excerpt/9780521847049_excerpt.pdf

"  It turns out that the scale at which the galaxy distribution becomes homogeneous is difficult to determine. From the analysis of the Sloan Digital Sky Survey (SDSS) it has been concluded that the irregularities in the galaxy density are still on the level of a few per cent on scales of 100 h−1 Mpc (Hogg et al., 2005). Fortunately, we know that the geometry of the Universe shows only small deviations from the homogeneous and isotropic background, already on scales of a few Mpc..

The geometry of the Universe can be tested with the peculiar motion of galaxies, with lensing, and in particular with the cosmic microwave background (CMB). The small deviations from homogeneity and isotropy in the CMB are of uttermost
importance since, most probably, they represent the ‘seeds’, which, via gravitational instability, have led to the formation of large-scale structure, galaxies and eventually solar systems with planets that support life in the Universe. (  If ‘analyticity’ is not assumed, the matter distribution could also be fractal and still statistically isotropic around each point. For a detailed elaboration of this idea and its comparison with observations see Sylos Labini et al. )  "

Actually both analyze it through the lens of relativity. And myself I think those two goes together as one principle, homogeneity and isotropy, when describing this universe. If one accept that, the way isotropy may differ becomes a connection to the Big Bang.


Maybe something of a simplification but if you find something to be homogeneous it should be isotropic too, and it doesn't state anything about a dimensionality, you standing on a sphere will find isotropy in all directions without a 'edge'.
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Turned the words around above, so I needed to correct it.  You don't get homogeneous from isotropic but you can get isotropic if you find it to be homogeneous.  Or maybe both can be correct?   Depending on definitions?

https://theeternaluniverse.blogspot.com/2009/08/what-is-homogeneity-and-isotropy.html

" Is there a space that is isotropic and not homogeneous?  The answer is no, isotropy implies homogeneity so I can't give a cool example of this unfortunately. "  Well, that's how I thought first.

Then you take this. 

"  If a region is homogenous then it's automatically isotropic around every point. If every point is the same then you can stand anywhere you like and look any direction you like and you're going to see points that are just like where you're standing. Therefore every direction is going to look the same.

The reverse does not apply. If what you see is isotropic then all you can say is it looks the same. Often, if your view is isotropic, then your surroundings are circularly or spherically symmetric, but there's no guarantee."

https://www.quora.com/What-is-homogeneity-and-isotropy-of-space-time-with-example

Soo :)                   Pick a choice.


(  well, I connect it to a lot other things in physics, and they all fit together to me. So I will call them two sides of the same coin. Which should mean that the sentence becomes   ' Maybe something of a simplification but if you find something to be Isotropic /or/ homogeneous it should be homogeneous /or/ isotropic too'   )

Physics :)

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Physics, Astronomy & Cosmology / Re: Is space in, beyond and around the universe?

« on: 27/06/2021 14:11:12 »

You might be able to define it as there are laws, properties etc that defines our universe. And as far as those exist, so do our universe. It doesn't say anything about a size or if it is inside or for that sake outside anything else. Looking at it this way a singularity is anything not obeying the laws and physics we know. So a 'black hole' is indeed a black hole to us :) And it expects this universe to behave much the same way everywhere and at any time.

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Just Chat! / Re: Mathematics is a decent science.

« on: 17/06/2021 14:42:39 »

You have a good point there Origin, but it's also about what type of mathematics one use. String theory has its own f.ex.. I'm no expert on in, but I've noticed elsewhere that the mathematics used seem to differ with what discipline you work under. And the ones wondering may not want it in pure mathematics, as you might lose them. Which is why I think, and as I noticed here, most people explain their variables and define them, as well as whatever equation might be involved. I think it's important to do it that way.
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That's probably the difference between what TNS wants to be and what f.ex physicsforum look for. Haven't checked but I would expect them to have a mathematical section there. That doesn't mean that TNS couldn't have it too, but I'm not sure it fits its guidelines?