0 Members and 1 Guest are viewing this topic.
I'm a newbie here and don't have any credentials to speak of...
Quote from: jeffreyH on 16/05/2017 19:40:29Let's say I have an object on the top shelf of a cupboard. I reach up and pick it up and lower it very, very slowly down to the bottom shelf. All the time gravity is acting against my arm. Since I am lowering the object I am removing potential energy. However I am using a lot of energy over the extended time period. So how much potential energy have I removed?In the course of moving the object down from the top shelf to the bottom shelf, you've removed the same amount of potential energy from it as you added to it when moving it from the bottom shelf to the top shelf. The energy that you're losing while holding the object against the force of gravity is not coming out of that store, as we can see by comparing you holding the object out at arm's length and getting tired as you use lots of energy to hold it up while a robot could hold it up in the same way but lock its arm so that it can keep the object there without using up any energy.
Let's say I have an object on the top shelf of a cupboard. I reach up and pick it up and lower it very, very slowly down to the bottom shelf. All the time gravity is acting against my arm. Since I am lowering the object I am removing potential energy. However I am using a lot of energy over the extended time period. So how much potential energy have I removed?
Quote from: David Cooper on 16/05/2017 20:39:44Quote from: jeffreyH on 16/05/2017 19:40:29Let's say I have an object on the top shelf of a cupboard. I reach up and pick it up and lower it very, very slowly down to the bottom shelf. All the time gravity is acting against my arm. Since I am lowering the object I am removing potential energy. However I am using a lot of energy over the extended time period. So how much potential energy have I removed?In the course of moving the object down from the top shelf to the bottom shelf, you've removed the same amount of potential energy from it as you added to it when moving it from the bottom shelf to the top shelf. The energy that you're losing while holding the object against the force of gravity is not coming out of that store, as we can see by comparing you holding the object out at arm's length and getting tired as you use lots of energy to hold it up while a robot could hold it up in the same way but lock its arm so that it can keep the object there without using up any energy.If I keep my arm and the object it's holding stationary then I should be storing a constant amount of potential energy. In order to maintain that potential I inevitably lose energy in the fight against gravity. This is not a trivial point, though it does appear so upon cursory examination.
If I keep my arm and the object it's holding stationary then I should be storing a constant amount of potential energy. In order to maintain that potential I inevitably lose energy in the fight against gravity. This is not a trivial point, though it does appear so upon cursory examination.
Sometimes a force carrier would need to add energy to the object (e.g. a falling object) while at other times it would have to remove energy from it (a ball being thrown upwards). It simply doesn't make sense, unlike my new way of looking at things where the shift between adding energy and removing energy makes full sense.
Quote from: jeffreyH on 16/05/2017 23:10:36If I keep my arm and the object it's holding stationary then I should be storing a constant amount of potential energy. In order to maintain that potential I inevitably lose energy in the fight against gravity. This is not a trivial point, though it does appear so upon cursory examination.The robot with locked arm is able to hold the object without constantly putting energy in, so you need to think about why you need to expend energy when the robot finds it unnecessary to do so. (The Box has called this one right!) It's an interesting question though as to why we have to burn energy to hold things up. If we don't hold it at arm's length it isn't so hard - if you balance it on your head it is little trouble to hold it high up. It appears to have something to do with crushable things using energy to avoid being crushed. Once crushed, the forces balance without energy being expended. That would be the basis of an interesting discussion that should maybe have its own thread.
The robot also expends the energy it needs to run the robot.
Quote from: Thebox on 19/05/2017 13:56:24The robot also expends the energy it needs to run the robot.The robot can lock its arm and switch itself off, leaving the object held up for as long as you like without any power being used at all.
When you lift an object, you are causing the fabric of space to accommodate it differently, and that involves putting energy into that fabric. This is like with bubbles in washing-up water which can accelerate towards each other as the surface tension rearranges the shape of the surface in order to minimise the amount of energy stored in it - that stored energy is turned into kinetic energy in the same way, and then it becomes heat. Once we understand where the potential energy is stored, it's all becomes obvious - all we have is a stressed fabric trying to get to a lower energy state.
Think of a photon box. This box is a bunch of photons with mirrors on all sides. If time slows down on one side of the box or equivalently the frequency lowers then the energy of the photons hitting that side of the box will be LOWER. If the photons leaving the mirror further in the gravity well are red shifted heading up to the top mirror they will hit it with lower energy. If the photons heading down from the top mirror are blue shifted they will hit the bottom mirror with HIGHER energy.
Light does not have momentum. It neither slows down nor speeds up. That violates relativity's postulate.
Light does not change frequency once produced.
It can slow down, and it stops if it's at the event horizon of a black hole while "moving" outwards.
Quote from: David Cooper on 05/06/2017 17:16:23It can slow down, and it stops if it's at the event horizon of a black hole while "moving" outwards.You cannot create light within a BH and all light bends around a BH. Light is not attracted to or by gravity. Light bends around the dilation caused by gravity. A BH has the greatest dilation of energy since there is no energy within a BH. Its completely kinetic with no energy available to run a clock.
Light does not have momentum. It neither slows down nor speeds up. That violates relativity's postulate. Potential energy is just that. Tick rate and energy potential slows to the center of mass. Energy is dilated so energy particles are further apart. Light produced in lower energy potential has a longer frequency due to particles being further apart in the position of space more dilated. That approach is indistinguishable with momentum and does not violate relativity postulates. Light does not change frequency once produced.
I've heard a description along those lines before, but I failed to consider all the implications, perhaps because there's a key part of it that doesn't add up. If the photon speeds up as it climbs out of the energy well, that extra speed energy should exactly balance out the loss in energy from the reduction in frequency, leading to the photons hitting the top and bottom of the box with exactly the same energy. Perhaps I'm missing something?However, you've certainly shown me that the potential energy can be stored much more simply than I'd imagined - when you lift an object, it's functionality speeds up (and has to speed up) and you have to put the extra energy into it to enable that faster functioning. That's something I'd completely missed before.
(makes you wonder if the inside solution for a black hole in GR is just completely wrong)
The bottom mirror receives more force and the top mirror less force. This unbalance requires an acceleration to counteract the red and blue shift.
I discussed a lot of Relativity in my thread "Different View of Relativity." I did a thorough proof of how length contraction naturally arises when all particles are treated as waves (best done in the third post I did in that thread).
I don't know if anyone has a viable proposed account of what happens in black holes. I wonder if any information about how things behave inside them is coming from the gravitational wave data.
But the forces must be transferred through the material of the box from top to bottom and bottom to top to affect the whole thing and they surely must in the course of that transfer be amplified or reduced as they are passed down or up, leading to an equalisation for both directions and no acceleration of the box.
You could create light just outside the event horizon from a laser pointing directly upwards. That light would be very slow at moving upwards, but it would move straight upwards and not go round and round the black hole instead, although any error in the direction it's pointing could lead to it going round the black hole instead, but any part of the light that is aimed absolutely straight up should go straight upwards (at a crawl).
QuoteI don't know if anyone has a viable proposed account of what happens in black holes. I wonder if any information about how things behave inside them is coming from the gravitational wave data.Well many scientists think they do all the way down to a very close distance to the singularity. However, many other scientists admit they don't know. Inside of a blackhole is outside of science if GR is correct because we can't observe in there. No observation, no science. The physics community overwhelmingly agrees they don't have a full solution that makes sense yet. Many scientists and pop culture often raises some of the far out predictions of GR to fact when they're far from it. Questioning General Relativity is often seen as heresy which I find counter to the principles of science. Gravity is modeled as the curvature of spacetime that does not mean this model is fundamentally right just that it seems to work well because the model matches many experiments. Newtonian Gravity still works well but it's ideas aren't fundamentally right.Gravity waves just like anything else don't convey information about what's inside a blackhole. If they do then GR is wrong.
That's the key to this - the light isn't red-shifted or blue-shifted on the way out of or into a gravity well, but is merely perceived as being shifted by something that measures its frequency at different heights. That means that the photons are hitting the top and bottom of the box with the same energy and it's merely being perceived as being higher or lower in energy.
The robot with locked arm is able to hold the object without constantly putting energy in, so you need to think about why you need to expend energy when the robot finds it unnecessary to do so. (The Box has called this one right!) It's an interesting question though as to why we have to burn energy to hold things up. If we don't hold it at arm's length it isn't so hard - if you balance it on your head it is little trouble to hold it high up.