How does time work?

[Cerveny]

As for your "growth/crystallisation", it's an interesting idea, but how do you account for the observed galactic redshift?

Universe crystallizes from the Future. Vacuum (its history) is an ideal crystal. Elementary particles are some structural defects in it (see screw dislocation, eg). The time of Now is some kind of (live) phase border between the History and the Future. The solid History is just setting, built during a rather accidental quantum interactions (“measurements!?”). Before “Big Bang” was only “Future” - the Platonic’s Empire if Ideas...

Again, it's an interesting idea, but how do you account for the observed galactic redshift?

Red shift perhaps indicates that remote galaxies move faster. It does not directly imply some “Expansion” of space at all. What should be expanding? Nothing? Aether cells? Elementary particles? Quantum foam? Why? What mediator/ agent should manage it? Modified time flow? How? I am afreid Universe “expansion” is hopless nonsense. I believe in cold, phase transition like, beginning of our Universe/History. I personally would never dare to defend the theory of Expanding Universe (from the Nothing) to ones, possesed logic, certain Physics knowledge and common sense. Hardly to believe such obscure “theory” would have had any chance to meet quantum physics environment:(

[uwot]

Another way of measuring mass is resistance to acceleration. The faster something is going, the more energy you have to give it to achieve the same acceleration.

Hate to disagree, but this seems misleading.

Feel free. It's always good when people who know what they are talking about pull me up on stuff.

Acceleration is a function of force and mass, not energy. F=mA, or A=F/m.

Yes, but E=mc2.

So for instance the ISS accelerates at all time due to the force of gravity on it, yet no exchange of energy is involved.

Not unless it crashes into Earth.

In frames where the object has relativistic speeds, the same force results in less acceleration because it is resisted by more mass. Newton's F=mA still works in under relativity. Energy again is not a factor. Kinetic energy is completely frame dependent and thus not really a property of anything.

Yes, but an objects mass is determined by its resistance to acceleration, which itself is frame dependent and not an intrinsic property of anything either.

At low speeds accelerating a particle a few mph takes very little energy, whereas at close to the speed of light, you need something as powerful as the Large Hadron Collider to squeeze the same few mph out of a particle.

The LHC needs all that energy because the particles get so massive in the frame of the LHC, and in addition, most of that force generated by the energy expenditure is wasted getting the particle to turn and not so much getting it to speed up. The larger the radius, the more force can be devoted to speed and less to turning. Still, the round ones get more speed than do the linear ones. I guess total travel distance makes more of a difference than does the percentage of force that is not orthogonal to the particle's velocity.

Well yes, a linear accelerator of the requisite length isn't really practical.

[Noax]

Acceleration is a function of force and mass, not energy. F=mA, or A=F/m.

Yes, but E=mc2.

How is that relevant? Does it invalidate F=mA? Doesn't seem to on cursory inspection, but I wonder. In an inertial frame where Earth is moving at .86c along the orbital axis of the ISS, 4x the force on the ISS if Newton's law of gravitation holds at relativistic speeds, which it apparently doesn't, but twice the mass and half the acceleration. F=mA might need relativistic adjustments. The gravitation law is clearly in such need, so my calculation of 4x force is wrong. I think it all works if Newton's gravitational law is adjusted for not the product of the two masses, but the product of the two rest-masses. Now F is unchanged. Frame independent F is = 2x mass * 1/2A. F=mA seems valid even under relativity.

Feel free to critique that. I just worked it out without consult a book or anything.

Still no energy expended anywhere to achieve that acceleration. Energy expenditure not required for acceleration. That was my point. Energy is needed to increase speed (and thus kinetic energy), but acceleration does not necessarily increase speed. The same kinetic energy increase in one frame is a kinetic energy decrease in the same object in a different frame. There is actually little connection between acceleration and energy expenditure because one is real and the other purely abstract.

Yes, but an objects mass is determined by its resistance to acceleration, which itself is frame dependent and not an intrinsic property of anything either.

I think I said that.

At low speeds accelerating a particle a few mph takes very little energy, whereas at close to the speed of light, you need something as powerful as the Large Hadron Collider to squeeze the same few mph out of a particle.

For multiple reasons, yes. The particle masses more at high speeds, so the same force yields less acceleration. Energy is work which is force*distance, and that increased force must be multiplied by ever increasing distance traveled by that high speed particle.

[uwot]

Acceleration is a function of force and mass, not energy. F=mA, or A=F/m.

Yes, but E=mc2.

How is that relevant? ... F=mA seems valid even under relativity.

Well yes, but relativity is just a model that deals with convenient variables like force, mass and acceleration. From an engineering point of view, how do you build a space station that can go round the Earth 4 or 5 times a second without blowing itself to atoms?

...There is actually little connection between acceleration and energy expenditure because one is real and the other purely abstract.

So which is which?

[Noax]

Yes, but E=mc2.

How is that relevant? ... F=mA seems valid even under relativity.

Well yes, but relativity is just a model that deals with convenient variables like force, mass and acceleration. From an engineering point of view, how do you build a space station that can go round the Earth 4 or 5 times a second without blowing itself to atoms?

I could compress Earth into a black hole, toss in the other planets and about 60 more solar systems worth of planets. That will getcha the ISS orbiting at about that pace (by whose clock??) at its current orbital radius, but its still going to get blown to atoms, and even if there was a material that could withstand that, the occupants would not survive it. Engineering failure it seems... but I didn't need E=mc2 to do that.

...There is actually little connection between acceleration and energy expenditure because one is real and the other purely abstract.

So which is which?

Poorly worded on my part. There is actually little connection between acceleration and kinetic energy because the former is real and the latter purely abstract. If something is accelerating, it is doing so in any frame (fixed force, not fixed A), and thus is real, but there always exists a frame where something's kinetic energy is zero, so assigning it that sort of energy is purely an abstract mathematical choice, not a real property of the object. There is a real (frame independent) kinetic energy relation between any two objects, which is zero if they have identical velocity.
As for energy expenditure, I can accelerate with or without it. The ISS expends no energy to accelerate. My house expends no energy to counter the force of gravity, but the rocket hovering right next to it does. So not abstract, but also not directly implied by acceleration.

[uwot]

I could compress Earth into a black hole, toss in the other planets and about 60 more solar systems worth of planets...

Let me know when you plan to do this. I'll make sure I'm down the pub.

There is actually little connection between acceleration and kinetic energy because the former is real and the latter purely abstract.

I take your point, but is that really the reason?

If something is accelerating, it is doing so in any frame (fixed force, not fixed A), and thus is real...

Ah, so we only feel a force if we are accelerating away from a massive object, but feel nothing if it accelerates away from us? Actually, forget the massive object. If the entire universe, even if empty (yeah, I know), drops from our feet, there is no force? What did happen to Newton's bucket?

...but there always exists a frame where something's kinetic energy is zero.

Its own, until it hits something else.

... so assigning it that sort of energy is purely an abstract mathematical choice, not a real property of the object.

Well yeah, what an object happens to be doing is not an inherent property.

There is a real (frame independent) kinetic energy relation between any two objects, which is zero if they have identical velocity.

That's the epistemological nature of relativity. There is no relation if they have identical velocity.

As for energy expenditure, I can accelerate with or without it. The ISS expends no energy to accelerate.

True, but it took a whack of energy to get it into an orbit that maintains its freefall, at least in our frame. Same with the Earth and Moon, neither of which need an input of energy to sustain their orbits, but if they bumped into a 'stationary' object (yeah I know), there would be a bit of a kerfuffle.

My house expends no energy to counter the force of gravity, but the rocket hovering right next to it does. So not abstract, but also not directly implied by acceleration.

If you do ever shrink the world to a black hole, you will quickly find out where all that gravitational potential was being stored. But when you really get into it, the the deformation of the atoms in your foundations will increase their energy, which, on the other hand, maybe offset by the greater centripetal force in your attic. Ya know? It's going to take a motherfucker of a computer to account for everything and work it all out.

[Noax]

I could compress Earth into a black hole, toss in the other planets and about 60 more solar systems worth of planets...

Let me know when you plan to do this. I'll make sure I'm down the pub.

https://xkcd.com/1680/

There is actually little connection between acceleration and kinetic energy because the former is real and the latter purely abstract.

I take your point, but is that really the reason?

Seems unintuitive, no? Angular kinetic energy is quite real, so why not linear kinetic energy? There's a symmetry that seems to be missing, the way I put it.

If something is accelerating, it is doing so in any frame (fixed force, not fixed A), and thus is real...

Ah, so we only feel a force if we are accelerating away from a massive object, but feel nothing if it accelerates away from us?

Presence of an imbalanced force (and the resulting acceleration from that) and ability to feel said force are two different things. You can't feel a uniformly distributed force, but barring a counter-force, you accelerate nonetheless.

Actually, forget the massive object. If the entire universe, even if empty (yeah, I know), drops from our feet, there is no force?

I don't think an empty universe dropping from our feet is distinct from it staying put. But if <everything else> does that, yes, there must be a force accounting for it. Principle of relativity doesn't say the two situations (me accelerating, or everything else accelerating) are equivalent.

What did happen to Newton's bucket?

Excellent example of angular velocity (and angular kinetic energy) being real.

There is a real (frame independent) kinetic energy relation between any two objects, which is zero if they have identical velocity.

That's the epistemological nature of relativity. There is no relation if they have identical velocity.

They are stationary relative to each other. That statement sounds like a relation to me.

Same with the Earth and Moon, neither of which need an input of energy to sustain their orbits, but if they bumped into a 'stationary' object (yeah I know), there would be a bit of a kerfuffle.

The process of the Earth acquiring its moon in the first place was itself quite a kerfuffle. I like the word. Yes, the ISS needed plenty of energy to accelerate it into its current trajectory. I spent a bit of time trying to figure out how it could be done without an increase in entropy, and it got weird, but could be done. Had to invoke chaos theory and 3-body problem to do it.

My house expends no energy to counter the force of gravity, but the rocket hovering right next to it does. So not abstract, but also not directly implied by acceleration.

If you do ever shrink the world to a black hole, you will quickly find out where all that gravitational potential was being stored.

Gravitational potential is negative energy, meaning there is no limit to how far you can fall, but you can only climb so high out of your gravity well before hitting the ground state of 0 potential energy. If the earth were compressed into a black hole, it would no longer hold the house at a fixed radius. The house would fall.

But when you really get into it, the the deformation of the atoms in your foundations will increase their energy, which, on the other hand, maybe offset by the greater centripetal force in your attic.

Quite right. The house would be torn apart by the tidal forces you describe before it fell into that black hole. I'm assuming it falls straight in, which is unrealistic. In fact it has some angular momentum, and so would assume an elliptical orbit, or it would if it could stay together. It happened recently on Saturn. Some moon got too close.

[attofishpi]

Everything you ever wanted to know about time: http://willijbouwman.blogspot.co.uk

Time is purely and only...the occurrence of an event. An electron emitting a photon for example.
In a moment of time, there is nothing occurring.

A moment in TIMe eMIT, and of course that includes whatever constitutes consciousness....in a moment of time.

If there is not an event, then there is not time.

[Impenitent]

if there is no spectator, there is no event

-Imp

[attofishpi]

if there is no spectator, there is no event

-Imp

I'm sorry to have interrupted an intelligent debate between two people where most of it barely made an itch to the crown of my head, but IMP, I disagree. If that was the case, evolution (of spectarors) would have a hard case.

[Impenitent]

if there is no spectator, there is no event

-Imp

I'm sorry to have interrupted an intelligent debate between two people where most of it barely made an itch to the crown of my head, but IMP, I disagree. If that was the case, evolution (of spectarors) would have a hard case.

a lack of immediate empirical evidence tends to do that

-Imp

[uwot]

Angular kinetic energy is quite real, so why not linear kinetic energy? There's a symmetry that seems to be missing, the way I put it.

I'm quite happy to concede that linear kinetic energy is real. While it is true that for epistemological purposes, you can in special relativity treat anything as if it were stationary, the chances of it be so are somewhere between nil and not much. So yeah, I think we agree on that.

There is a real (frame independent) kinetic energy relation between any two objects, which is zero if they have identical velocity.

That's the epistemological nature of relativity. There is no relation if they have identical velocity.

They are stationary relative to each other. That statement sounds like a relation to me.

Fair enough. Badly worded on my part.

[uwot]

if there is no spectator, there is no event

-Imp

How could we tell?

[uwot]

Red shift perhaps indicates that remote galaxies move faster. It does not directly imply some “Expansion” of space at all.

So where are they moving to?

[Impenitent]

if there is no spectator, there is no event

-Imp

How could we tell?

who could we tell?

-Imp