Science a GoGo's Home Page Forums General Discussion Physics Forum Looking at gravity

https://www.youtube.com/watch?v=MTY1Kje0yLg

It's just another look at the rubber sheet analogy, but I liked this one, especially as it introduced dark energy.

Downside? It's stirred up all those unanswered questions about gravity.

Is it a force, or not?

Does mass expend energy in warping spacetime, and maintaining the curvature?

Etc, etc......

You can partly address some of your questions by realizing that in the video they had to clamp the fabric to a rigid frame to hold it taunt. Without that the whole thing would have collapsed in a bundle as would space collapse if there was not something holding space "stretched out" in their layman analogy.

That leads to the concept of a stress-energy tensor in relativity (Bill G and Rede didn't get that in a rather funny exchange on dark energy).

Background reading:
http://en.wikipedia.org/wiki/Stress-energy_tensor

So under Einstein relativity do you get what is proposed that stops the universe collapsing in on itself?

Hint: It's easy to see in EM and Radiation because they tend to radiate and spread out but not so obvious with matter because there are binding attractive forces to add in.

We could also tag two other pieces of information that will add in some useful things to consider in looking for a answer.

1.) Anything that moves gives off radiation. Your question to ponder is where does the energy come from?

2.) A not often understood fact from QM is that due to the uncertainty principle the bigger something is the tighter it can be packed. That is why the larger particles pack together in the nucleus of an atom. That is why even in a neutron star and beyond there are limits to the force gravity can exert as it tries to squeeze all the matter to a singularity and it must deal with QM. We refer to the process as degenerate matter (http://en.wikipedia.org/wiki/Degenerate_matter). If nothing else try to read and understand the concept section.


So there are things outside the simple picture and questions you asked to think about. Forces can be limited in really interesting ways that don't immediately come to mind in classic physics.

Thanks, Orac; quite a lot to think about, there.

The thing that “jumps out” of your post is the question: “…where does the energy come from?” You probably recall that I have been asking that question about gravity, in one guise or another, for some considerable time. I think I even proposed an answer once. I would like to come back to that when I have had time to follow your links.

In the meantime, I have taken the next step in my own (layman) thought process, and as usual, present it as though I were explaining it to someone else.

Let’s start with a 2D image. On a sheet of paper, draw a circular spot to represent the gravitating body. According to GR, this body causes spacetime around it to bend. At some distance from the body draw a smaller spot to represent an object approaching the body. It is in uniform motion, so draw a straight line to show what the trajectory of the object would be if the body were not there. Now draw a line to represent the trajectory of the object, with the body present, such that the object is diverted by the curvature of spacetime, but not captured. Next draw a line to show the object going into orbit around the body.

All this fits the spacetime curvature scenario quite well. There are a few questions that arise, but at first glance they may not be obvious. Before you part with your sketch, draw a line representing the trajectory of the object if it is travelling straight towards the centre of the body. In this case, the curvature of spacetime will influence the object equally from both sides – we are still working in 2D – so the line will remain straight, there is no change in direction. There is, however, a change in the objects progress towards the body. As gravity takes hold, the object will accelerate. This is where an alarm bell rings. Somewhere from the depths of memory a Newtonian equation begins to emerge. F = ma. Force equals mass times acceleration. Whichever way you rearrange this equation, the force is still there. What is that force, if it is not gravity?

Whether gravity is a force depends, I think, on how you look at it. If you think of it as something that pulls you toward a massive object then it is a force. If you look at it as curved spacetime then it probably is just considered as a natural path, no real force required. Of course either way you look at it it acts like a force. That is it causes movement vectors to become curved so I will probably keep talking about the force of gravity.

In regard to mass expending energy to warp spacetime, My first thought is yes, but I'm not sure about how it works. The thing is that in order to have a mass expend energy in warping spacetime I have to go back to a thought experiment that never happens(1). If a mass suddenly appears in an "isolated" location spacetime will be warped. In that case energy will be required to create the warp. I assume that the energy comes from the mass creating the warp. That is a small amount of the energy required to create the mass, wherever that came from, will be expended in creating the warp. Of course for existing masses no further energy expenditure would be required to maintain the warp.

Then there is the energy of motion. Any kind of motion will of course cause changes in the warpage. Such changes will require energy and that energy comes from the motion. In other words anything that is moving is losing some of the energy of motion and slowing down. That is the source of gravity waves. Of course the amount of energy lost to gravity waves is normally very small. We can effectively ignore gravity waves when calculating the orbit of the Earth around the Sun.

(1) I am ignoring the question of where the mass of the universe came from prior to the big bang. Let's not go there.

Bill Gill

http://en.wikipedia.org/wiki/Degenerate_matter

“Imagine that a plasma is cooled and compressed repeatedly. Eventually, it will not be possible to compress the plasma any further, because the Pauli exclusion principle states that two fermions cannot share the same quantum state. When in this state, since there is no extra space for any particles, we can also say that a particle's location is extremely defined. Therefore, since (according to the Heisenberg uncertainty principle) ΔpΔx ≥ ħ/2 where Δp is the uncertainty in the particle's momentum and Δx is the uncertainty in position, then we must say that their momentum is extremely uncertain since the particles are located in a very confined space. Therefore, even though the plasma is cold, the particles must be moving very fast on average. This leads to the conclusion that in order to compress an object into a very small space, tremendous force is required to control its particles' momentum.”

I have a problem here. In the case of a particle that is free to move, its momentum can be measured, but, because it is moving, its position at any given time will be unknown. If its position at a given time is known precisely, then its momentum will not be known, but it is reasonable to assume that a second measurement of its position would reveal that its position had changed. It would not be possible to infer its momentum from this change in position because there is now way of knowing how it moved from position 1 to position 2. E.g. it could have taken all possible routes, or only one.

Is that reasoning correct?

The quote from Wiki seems to be saying that the plasma is compressed to a point where no further compression is possible, so the location of each particle “is extremely defined”. In spite of this maximum confinement the particles are “moving very fast on average”. How can they be moving if they have no space in which to move? Alternatively; how can they be still and have their positions “extremely well defined” without violating the HUP?

We seem to be thinking more or less along the same lines. The next step in my process went something like this:

When we move from 2D to 3D the usual explanatory image is that of the gravity well, which emerges directly from the rubber sheet analogy. The mass (usually represented by a bowling ball) depresses the sheet, and any passing object that comes close enough is diverted from its straight line course and may enter orbit around the mass.

Newtonian mechanics tells us that diverting the object from its straight line requires input of energy. A force must act on the object in order to divert it towards the mass. Does relativity change this? Relativity says that in following curved spacetime the object is following a geodesic. A geodesic is defined as the most direct route in curved spacetime. A geodesic seems to have a lot in common with a straight line. Could it be that a straight line in Euclidian geometry is equivalent to a curved line in the non-Euclidian geometry of curved spaces? Would it follow from that that, given an appropriate change in geometry, no force, and therefore no expenditure of energy, is required to alter the course of the object?

In a way, that would be a convenient line of reasoning, but, unsurprisingly, it leads to other problems.

You are applying a very classical concept remember the particle movement is more than just the kinetic classic physics movement it includes oscillations, spins and quantum vibrations. To try to give some classical relationship think of the typical ice skater spin they come skating in with speed and turn lateral movement into enormous rotational spin speed.

That is the classical version there is the same possibility in the quantum modes and it was explained thus

So the particles are locked in your classical movement world but exhibit incredible vibration in the other degrees of freedom. If you like as in the ice skater example gravity is trying to lock the position to one physical location but the particle is then forced to shifting the uncertainty to the other degrees of freedom as the energy must go somewhere like spins and vibrations.

So in the classic world you would measure the plasma as cold as it's not moving in classic 3d space but there is still extreme uncertainty about which way it's spinning, vibrating etc. If you tried to touch the plasma as with trying to touch the spinning skater you would find out just how much energy it really contains.

That is exactly what it is

http://en.wikipedia.org/wiki/Geodesic
=> In mathematics, particularly differential geometry, a geodesic is a generalization of the notion of a "straight line" to "curved spaces".

The equator is the maximal geodesic of the earth.


So we could ask if the earth was all land does the amount of energy we require to walk or drive around it vary at any point if we are moving along a geodesic.


I would be interested in what problems you think there are because this is all very classical. If we had the all land earth above and there was no friction and I rolled say a ball what would happen?

If the Earth was all land and there was no friction the first thing that would happen is you would be propelled backward by an amount of energy equal to the energy you used to roll the ball. The ball would eventually roll back around to where you let go of it, and you would eventually slide back to where you were when you let it go. The ball, having less mass, will travel faster due to its greater momentum vs. mass. So you would pass the ball eventually, but at a point nearer to the origin than the ball.

When you specify no friction, all sorts of things become possible. :-)

The sillier among us have a large ball going forward and you going backward until the ball hits you behind the knees and knocks you flat. Of course this does not stop your motion, so next time it hits you on the head. Thank goodness for friction.

I’ll be happy to return to the problems, but they might constitute a digression from the current “flow”.



Discounting surface irregularities, no, but we are permanently following the geodesic. Even when we feel as though we are travelling in a straight line we are still following the geodesic. Is that the same as travelling in a straight line in space, then transferring to a geodesic?

That seems like a very reasonable view, but it links to the problems I hope to return to. Hold that thought.

Correct x 2

The key point is no energy was lost or gained while rolling around the geodesic and the balls energy is unchanging. So constant motion or stationary objects can both have a constant amount of energy. We could take the idea further and spin the ball and now roll it around the earth and now it has even more complex motions yet the energy remains constant.

So constant energy does not require simple straight line motion or no motion it can occur in the most complex movements.

Nothing changes in relativity with spacetime your ball is still rolling along a geodesic which has the same relative time and so no energy is lost or changed. However rather than need a force of gravity to hold the ball against earth like classic physics the ball is trying to run down the energy gradiant provided by the change in time towards the centre of earth and it is that energy gradient that holds it against the earth. The two situations are indistinguishable under classical physics tests you are simply replacing a force with an energy gradient.

You obviously need to do different tests like to see if time changes in the presence of a gravitational source.

You still aren't seeing the problem how would you ever know if you are traveling in a straight line in space

Even if I travelled directly at a close target say the moon. The milky way galaxy and our solar system are rotating and moving so I ask in what sense am I travelling to the moon in a straight line?

For the record:
The rotation speed of earth relative to the centre of the galaxy is 220 km per second, or 490,000 miles per hour.
The milky way is moving at around 600 km per second or 1,342,000 miles per hour.
The flight time for apollo 11 was around 3 days to the moon (259200 seconds) and its fastest speed was 11km per second or 25,000 Miles per hour.

Calculate the galaxy movement distances in that time

Bonus points: Can you work out what the true path looks like if you plotted it from some point outside the galaxy. Hint for every 11Km along the "straight line to the moon" it rotates 220km and moves laterally 600km.

This is the problem of trying to create a zero frame for the universe which is actually what you are trying to do so you can work your classic energy calcs from there .. fun isn't it

Straight lines don't really exist in space, they exist only in some relative sense to some reference point that has some general movement similar to you. So above we talk about a straight line to the moon because we are sort of moving in relatively similar way to the moon but the actual movement is anything but a straight line

ABOUT EM RADIATION

http://en.wikipedia.org/wiki/Solar_sail

How body is generating CZERENKOW's Radiation


IN UNIVERSE EXIST N objects
N objects are sending N EM waves

Czerenkow ?


please try move in universe it is very similar situation to
swim

If You swiming under water You are pushing EM preasure
Your body is full of atoms ( atoms Joust like eats energy - absorbtion process )

Body that is moving joust makes TRAP

http://2.bp.blogspot.com/-iNHYy6u9bRg/VF9En99DNmI/AAAAAAAACFA/vOX3fZYchx4/s1600/em.jpg

I am aware that one should not talk of a straight line without reference to something. However, if a moving object which, in our F of R, we measure as being in uniform motion, relative to something, changes course, relative to that same something, we deem it to have accelerated, relative to that something, and conclude that the object has been influenced by a force. Our conclusion may be erroneous if the motion, and change in motion, are considered relative to some other something in another F of R, but within ours, I think it does not conflict with the laws of relativistic physics.

Returning to the gravity well, we have to ask how well the rubber sheet analogy illustrates the real situation. The gravity well of the rubber sheet analogy is really only a 2D illustration partially translated into 3D. The full 3D image would be practically impossible to represent on a sheet of paper. The mass becomes a sphere subtending a quasi-infinite number of gravity wells, impinging upon it from every direction. It might be tempting to visualise this as being like a sphere made up of closely packed gravity wells, like one of those paper Christmas decorations composed of closely packed hexagonal cones. Such would not be the case. In fact, every gravity well would have to overlap a boundless number of other gravity wells, such that if one imagines a sphere of any size centred on the mass, every gravity well would have to intersect the surface of that sphere so that its “mouth” formed a great circle. Any other configuration would not permit a stable orbit to be established by the object, irrespective of its direction of approach.

That's a problem with all the analogies we use to help us visualize how the universe works. We start off looking at them and saying "OK, now I understand that". Then if we start looking more closely we find that things just aren't that simple. To see the way it really is I generally just look at the analogy, then remind myself that is not the whole story.

When you (Bill S.) ask some of your questions I wind up getting all tangled up trying to figure out what is really happening. I am not saying your questions are inappropriate, except that they make me have to thing about them. And I really don't much like to have to think.

Bill Gill

How You want to recognize

force = gravitation or force = Em preasure

can You feel problem ?

http://1.bp.blogspot.com/-spFELf_xcJ0/U_CBPKLmCEI/AAAAAAAAB5M/FfYELmw3M6c/s1600/pytanie1.jpg


p1..p2..p3..me ---> motion

Bulb and rocket was in point p1
p2,p3 now is in point p4 will be in point p5

Please evaluate 45 degree problem ( two source )
how fast is rocket if EM preasure can not push rocket ?

ABOUT EM preasure
http://en.wikipedia.org/wiki/Solar_sail

Don't just wonder about it, Bill, ask, criticize, throw rocks! Most of my questions are asked because I'm trying to figure out what's going on, so any and all input is a bonus.

Shouldn't that have been "Calculate the galaxy movement distances" relative to something?

But that's the problem. To "ask, criticize, throw rocks" I have to stop and think about what is going on. And as I said, I don't really like to have to think. You keep posting things that force me to think to try to come up with good answers. It is easier if people say things that I already know are wrong and all I have to do is point out their errors.

Bill Gill

HOW BIG DENSITY HAS GOT GRAVITATION ?

!!! see what it is EM preasure
> http://en.wikipedia.org/wiki/Solar_sail


http://3.bp.blogspot.com/-mfX1X9yDqDw/VLuo2Th_6_I/AAAAAAAACNQ/YaGD36e4PRk/s1600/mar.jpg



N OBJECTS AROUND ME IS PUSHING ME IN SPACE

http://2.bp.blogspot.com/-gBZZDFieaMw/VFTf-NSO4PI/AAAAAAAACC0/s3Tu8OWG0QM/s1600/CIMG3376.JPG

HOW BIG FORCE I'm REGISTERING IF I'm moving ?
HOW BIG FORCE I'm registering IF I'm not moving ?

moving ? respect to what ?

p1..p2...p3...me >>> motion


p1,p2,p3,p4,p5 - points in space where I was , I will be


N OBJECTS AROUND ME ( I'm satellite for all objects not only for stupid EARTH )

http://4.bp.blogspot.com/-4AWDWMgFt-A/VG3AE0YY6WI/AAAAAAAACJs/Sxn-BZ1lvWQ/s1600/xxx3.jpg


EXIST LINEAR MOTION ?
ME AND EARTH ARE MAKING ROTATION WHY WE NOT HAVE PI in famous
reduction ? FLAT LASER ? OR FLAT THEORY ?

https://3.bp.blogspot.com/-LtSyL-h9ASY/VGR7uuAyWhI/AAAAAAAACGQ/axraHLUxois/s640/f.jpg


WE HAVE ONLY ONE OPTION INSIDE ROCKET ?

http://4.bp.blogspot.com/-rIRCHBzHWoc/VHQjXwkfFVI/AAAAAAAACLw/8DkBbdQL0_A/s1600/Eistein.gif

http://1.bp.blogspot.com/-HEnn7T9o9cw/VHOZTzOjBBI/AAAAAAAACLg/CoXd_JoyeI4/s1600/22.jpg



NEW PROBLEM FOR CLASSICAL MECHANICA ?

mV ---> <--- mV

above idea is very simle and not exist in real world
( physics it is real world not mathematica )



HOW HEAVY IS MASS M ? SYMTRY IN PHYSICS ?

30 km/s respect to table ( below drawing )
please evaluate problem "now"
and 12 h later after 180 degrees. Earth is making own rotation .
How heavy is Mass m left /right ?

http://4.bp.blogspot.com/-z7Ki0fNtLrY/VCqMhjWmV1I/AAAAAAAACA4/W5lTo-22NrI/s1600/CIMG3345.JPG


HEW PROBLEM INSIDE ATOM ?
ATOMIC CLOCK WHY INSIDE AiRPLANE ELECTRON IS CHANGiNG PERIOD

http://1.bp.blogspot.com/-sS8HdZmjYV8/VCkOc9JKdEI/AAAAAAAACAo/POHBAwU4OZk/s1600/CIMG3341.JPG

NOBODY BEFORE ME DESCRIBED ABOVE FORCE INSIDE ATOM
it is not my problem that I'm person who saw problem before others

I CAN NOT UNDERSTAND WHY IF NASA SEE PROBLEM

THEY ARE TRYING TO USE NEW THEORY ( QUANTUM SPACE FLUCTUATION )


NASA's raport http://ntrs.nasa.gov/search.jsp?R=20140006052





WHY NOT NOT VERY OLD KNOWLEDGE and Si units system

MAROSZ

EM preasure
> http://en.wikipedia.org/wiki/Solar_sail


http://1.bp.blogspot.com/-spFELf_xcJ0/U_CBPKLmCEI/AAAAAAAAB5M/FfYELmw3M6c/s1600/pytanie1.jpg


ROCKET IS MOVING OR NOT ? ( NASA LAB IS MOVING EUREKA!!! )

respect to what ?
respect to place where Earth was short time ago and where
EM drive started signal ...

JOUL/cubic meters =

= Newton * meter / cubic meter

= Newton /square meter ( dear Nasa EUREKA it is pascall )

Excellent you have made the connection, always be wary about your frame of reference.

Again excellent you have got the issue.

If you think hard there is only reference you can use which is energy. That is what your big reply above is trying to say when trying to talk about acceptable frames of reference and relative motions etc.

Hopefully you can now join the whole lot together by reading about planks constant. Initially try to skip around the quantum mechanics and follow it's history back into classical physics and the "fixation section" at the end should help with understanding all the connections.

http://en.wikipedia.org/wiki/Planck_constant

If you make the connections you should now see you have a complete framework referenced to energy via planks constant but the whole system has a small issue can you see what it is

Problem Hint: Read the significance of value section carefully.

We are getting some good stuff here, Orac.

A nagging thought at the back of my mind says: the original subject was gravity, we seem to be talking largely about quantum scale objects. Do we have a quantum theory of gravity? I understand not.

I am not here to give you an answer, you need to work out an answer for yourself that makes sense to you. I don't like the idea of standard consensus solutions in science

As I said you can ignore the QM stuff and look purely at the classical physics side. Planck and Einstein create QM in trying to solve part of the puzzle but pretend you are in 1900 and look at the data you have in purely classic terms and stay with gravity. Whether gravity is based in or with QM is not important at this stage we are looking at the classical situation.

Let me throw you a hint to ponder.

At the plank scale in classical terms space must be flat, you see this happen when you look at the earth beneath your feet. No matter what curvature space may or may not have if you reduce the section small enough the curvature disappears. The second point in relativity terms is your frame of reference gets very compact.

Sabine Hossenfelder deals with this is a technical way in this article (http://backreaction.blogspot.com.au/2013/04/black-holes-and-planck-length.html). I want you to think about this part of her statement and see if you can work out what she means and if you agree with her.



Unfortunately wikipedia doesn't really deal with the subject well but it does help you understand why this question is the most important with what you are pondering and I encourage you to think more about it.

http://en.wikipedia.org/wiki/Planck_scale

Edit: Bit of squirreling around and thanks to NASA's education outreach try reading this
http://arxiv.org/pdf/1001.1205v1.pdf

Orac, I've not lost sight of the fact that I have not responded to your last post. Hope to get to it soon.

If you are still interested in going on I will give you another interesting recent experiment by Martin Ringbauer et al

https://medium.com/the-physics-arxiv-blo...ne-185a7cc9bd11

Full paper:http://arxiv.org/pdf/1501.05014v1.pdf

It is a really interesting experiment on links between GR, QM and causality and worth reading.

Just get round to following links. Started with: https://medium.com/the-physics-arxiv-blo...ne-185a7cc9bd11

The first thing that strikes me is this:

“In the early 90s, for example, cosmologists showed that a billiard ball entering a wormhole that leads to a closed time-like curve must always meet its older self coming out of the wormhole. What’s more, the resulting collision always prevents the ball entering the wormhole in the first place. In other words, the billiard ball would simply bounce off the entrance to a closed time-like curve.”

Isn’t that just replacing one paradox with another? If the ball cannot enter the closed time-like curve, how did its older self get in there in the first place? I can answer that in terms of my "infinity theory", but who's going to accept that?

One would expect clever computer stuff from David Deutsch, for whom I have great respect, but I sometimes feel he blurs the line between computer programs and reality. Are you familiar with his ideas on the Omega Point Theory? I don’t know enough about computers to know how a nondeterministic algorithm reflects reality, but I suspect it would be only loosely.

To my very non-technical mind, it seems as though this experiment uses a simulated pair of entangled photons and treats them as though they were one real photon. Doesn’t that have echoes of claims relating to teleportation?

Don’t think I am knocking the work. Not only am I not qualified to do that, but I am fascinated by any work on time/loops/travel, and am keen to understand as much as possible about them.

As discussed before sometimes looking carefully at the question and changing it tells you things


Yes but there is a problem we discussed it above no actual singularity can exist because of the planck distance and uncertainty principle, you looked at the QM evidence and experiments. Even in string theory which can generally do anything you have to do some pretty interesting things to allow a singularity.

The idea and theory is therefore falsified unless you can somehow restore a singularity and so add that to the theory scrap heap like many others.

Remember the only indication for a singularity is indicated from GR and that is fairly fuzzy Matt does a reasonable job in
http://profmattstrassler.com/2014/03/21/did-the-universe-begin-with-a-singularity/


So are you and your father one entity or two. As far as we know there are only a limited number of humans that spontaneously appeared out of thin air and the same with entangled particles

The dependency between the existence is what is interesting.

As I recall, Deutsch’s idea did not involve a singularity. I’ve succeeded in finding a quote from him. He treats the survivors at the omega-point as the ultimate virtual reality rendering. He regards them as computers, into which the last remaining intelligent beings in the Universe have downloaded their intellectual “essence”. He describes the dying moments of the Universe, according to the omega-point theory, as follows:

“The key discovery of the omega-point theory is that a class of cosmological models in which, though the universe is finite in both space and time, the memory capacity, the number of possible computational steps and the effective energy supply are all unlimited. This apparent impossibility can happen because of the extreme violence of the final moment of the universe’s Big Crunch collapse. Spacetime singularities, like the Big Bang and the Big Crunch, are seldom tranquil places, but this one is far worse than most. The shape of the universe would change from a 3-sphere to the three-dimensional analogue of the surface of an ellipsoid. The degree of deformation would increase, and then decrease, and then increase again more rapidly with respect to a different axis. Both the amplitude and frequency of these oscillations would increase without limit as the final singularity approached, so that a literally infinite number of oscillations would occur even though the end would come within a finite time. Matter as we know it would not survive: all matter, and even the atoms themselves, would be wrenched apart by the gravitational shearing forces generated by the deformed spacetime. However, the shearing forces would also provide an unlimited source of available energy, which could in principle be used to power a computer. How could a computer exist under such conditions? The only ‘stuff’ left to build computers with would be elementary particles and gravity itself, presumably in some highly exotic quantum states whose existence we, still lacking an adequate theory of quantum gravity, are currently unable to confirm or deny. (Observing them experimentally is of course out of the question.) If suitable states of particles and the gravitational field exist, then they would also provide an unlimited memory capacity, and the universe would be shrinking so fast that an infinite number of memory accesses would be feasible in a finite time before the end.”

Thus, in the F of R of the “survivors”, the singularity would never arrive.

I’m not sure I can agree with the second sentence. Consider the flip-side of your thought experiment. There is a mass distorting spacetime, if that mass suddenly vanished, spacetime would revert to its original configuration. Spacetime must be trying to revert all the time that the presence of the mass is keeping it distorted. If you compress a spring, and hold it in the compressed state you will probably soon become aware that you are expending energy, just holding it there. Would the same not apply to a mass holding spacetime in a distorted form?

When you compress the spring and hold it there the energy you are expending is not really being used to hold the spring compressed. The energy is being used by your muscles to maintain the position. If you substitute a clamp for your hand then you will realize that there is no extra energy required because the system is in a state of balance. It will be the same for a static mass in a static universe. Adding or removing the mass will cause a ripple to move outward from the location of the mass. The ripple will carry energy that comes from the total energy of the mass and the gravitational field.

For a realistic universe with many masses of course everything will be moving, so the gravitational field will be rippling all the time. Think of stirring water. There will be ripples. The energy to create the ripples comes from the motion of whatever you use to stir it. In the case of a mass in a gravitational field the energy carried away by the ripples comes from the motion of the mass. For most objects, such as planets, the ripples will be so small that they are, for all practical purposes, undetectable. The energy loss, and thus a change in the velocity of the mass, can be calculated. It takes a long time for a planet to lose a significant amount of energy to gravitational ripples.

Bill Gill

Slowly cut through your clamp. As you do so, the spring will first deform, then break the clamp. That spring pressure has been there all the time; you don’t increase it by cutting the clamp.

Alternatively, consider that while the spring is being held in tension its molecules readjust; energy is lost as heat and the shape to which the spring would "return" changes. Could it be that anything like that would happen to spacetime if it is held in a distorted shape for a very long time?

Just a “what if”.

But there is no energy expended by the clamp when it is holding the spring. In the mass/space system there is no way to cut the clamp.

Again, the energy lost is for the specific case of the spring and clamp system. That is not an isolated system. In the thought experiment with just space and one mass Spacetime is the whole system, there isn't any place for energy to be lost to.

Bill Glll

That’s true. However, suppose the mass is ice, and it can somehow be vaporized. As it goes, spacetime will revert to its normal configuration. Energy must be involved in this change. So, is it true to say that spacetime in its distorted form has potential energy that is converted to kinetic energy as its shape changes? Thus, distorting spacetime has something in common with picking up a stone in a gravitational field, and placing it on a shelf. I.e. there is an exchange of energy while the stone is being lifted, and, again, if it is pushed off the shelf so that it falls; but there is no energy exchange while it sits on the shelf.

Well, as the ice dissolves the configuration will change. But the mass will remain the same. It will just be spread out. The change in energy will just be converted into the energy of motion as the water molecules move away from the location of the ice cube. The dip in the rubber sheet will get smaller, but a lot more dips will appear, one for each molecule. They will be small dips, but they will be there. And of course the interactions among the molecules will become very complex. It won't be as simple as an ice cube on a rubber sheet.

Once again remember that the bowling ball on a rubber sheet is only an analogy. The analogy helps us visualize what is happening, but the reality is quite a bit more complex than is shown in the analogy.

Bill Gill

Thanks Bill. I think I have the necessary bits for the jigsaw; all I have to do now is put them together to see what the picture looks like. All I have to do then is see if I can link it to Orac's QM. That might be more fun than anyone should have.

If you can link it to QM then you are way beyond me. In fact if you can link it to QM you are ready for a Nobel Prize. That is one of the big tasks that physics has today.

Bill Gill

Bill G your answers were absolutely correct to each of Bill S proposal you made the realization there was nowhere for the energy to be lost in the classic physics world. Now even at your basic layman level it isn't hard QM INFORMATION IS ENERGY yet you fail to adhere to the same logic.

In 1905 Einstein published the paper which won him the 1921 Nobel prize .... so your stupid statement was correct ... you did give me a good laugh as it was past tense he won the Nobel Prize

try reading => http://en.wikipedia.org/wiki/Photoelectric_effect it is the point in history that connects classical energy to QM energy.

I sometimes think you chose to be obtuse because you don't like the answers or perhaps just because it was my statement

Bill S, QM is explicit in the theory that there are no hidden variables (http://en.wikipedia.org/wiki/Hidden_variable_theory) and there is nowhere for the energy to hide. This was the point I was trying to get you to realize you are directly violating QM. If a Quantum Gravity theory exists (and Bill G's says it must it's in his "in" box) then the same argument holds and there is nothing "tricky" or hard about it.

So the memo is in any Quantum Gravity theory not a thing changes in that argument you would need to prove QM is wrong and hidden variables exist to make your argument work.

Bill S, if I could urge you to understand one thing it is that QM has central tenets as a theory in the same way classical physics has. Suggestions that contradict those tenets you need to look at very carefully, if only because of the vast number of supporting experiments to them.

Jester noted something most missed in discussions Planck/Bicep data that was the type of cosmic inflation favoured and relevant to your thread here if you can work it out.

Worth a read: http://resonaances.blogspot.com.au/2015/02/weekend-plot-inflation15.html

You might want to brush up reading on R^2 inflation.

Orac, my qualification and background in adult education make me well aware that pointing students in the direction of information they can research for themselves is better than spoon-feeding. I appreciate what you are doing, but there is a down side. As you know, I lack the scientific/math background, so just following your links tends to involve quite a lot of fill-in work. At approaching 75, that work is slower than it would have been 50-60 years ago.

As the main carer for two disabled people I find that time is distinctly scarce, so I frequently leave the work undone. Whilst I am always happy to provide “a good laugh” (I’m too thick skinned to bother about that) I have to look for shortcuts if I am going to answer any of the multitude of questions in my head. Less riddles and more hard info would be greatly appreciated.

If Orac can point us to a solid link between QM and GR nobody on the Nobel Committee has noticed it. Yes, there are problems with GR when you get into the QM range of lengths and energies. But nobody has been able to make reasonable predictions of GR phenomena using QM. They both work wonderfully in their respective areas. But there is still no way to bridge the gap between them, despite the fact that Orac seems to think that QM is the answer to everything. I figure one of these days somebody will come up with a testable solution that actually does work in both areas. Right now I have not heard of anything that actually seems to have much chance.

As far as giving links instead of hard info, I have been somewhat guilty of that myself. I have been having a conversation with monica1 over on the science section and have been posting links to wikipedia that I didn't bother to read myself. I suspect that monica would not have much success in deciphering them, based on the way she phrased her questions. It is awfully easy to get to doing that instead of working on figuring out how to say it myself. And as I said to monica, I am definitely not a teacher.

Bill Gill

The safest way that cause me the least flak is to guide you by prompting rather than tell you ... you only have to look at the stupidity answer of Bill G to see the issue.

There is nothing magical or tricky about the energy involved in QM it can be measured, used and converted just like it's classical energy counterpart. The QM description of what is happening is complete in every sense and can be described by maths and equations. If you extend QM to a Quantum theory of gravity it has to obey all those same standards.

The alternate is that gravity is not related to QM in any way and then fine it could have different rules but you need to realize these two choices are mutually exclusive.

A quantum theory of gravity that violates the central tenant of QM is not a quantum theory at all it is the 2nd option ... is that blunt enough.

Our resident crazy and his theory of gravity is an example of the second option.

And again how many times do you need me to tell you I don't think that at all before it comprehends to you ... or is this one of your obtuse Bill G moments again.

SO LETS REPEAT IT FOR ABOUT THE FIFTH TIME

QM PROVIDES NO ANSWERS AT ALL IN IT'S CURRENT FORM IT SIMPLY PROVIDES A DESCRIPTION OF WHAT IS HAPPENING IN THE UNIVERSE. IF YOU WANT ANSWERS YOU NEED A THEORY DEEPER AND CLOSER TO A THEORY OF EVERYTHING THAT EXPLAINS AND INCLUDES QM.

SO PLEASE DO NOT MISREPRESENT ME AND SAY THAT I THINK QM ANSWERS EVERYTHING .... THAT IS A BLATANT LIE AND COMPLETE RUBBISH

I try to not misrepresent your layman classic physics and beliefs and I would appreciate if you did the same with me. As this is not the first time you have made this wrong comment, it would be appreciated if you take time and let this sink in so you don't make the mistake again.

If QM is complete in every sense, then how does it apply to gravity? It seems that it must be incomplete if you can't explain gravity, in detail, using it. Therefore I don't see how you can claim that.

My claim is that neither QM or GR is completely correct and we need a new theory that encompasses both of them. Calling that theory quantum gravity seems to be a good thing to do, at least for now.

Bill Gill

Pointing the way is good, if it is done correctly. Unfortunately the way you are doing it is kind of like a swimming instructor who takes new students to the pool, throws them in the deep end and starts demonstrating the breast stroke. You need to start off with the basics. In swimming that would be how to float, how to breathe, and the basic strokes. In physics that would be the basics of physics, not the deeper math.

Bill Gill

You have assumed QM has something to do with gravity, last I looked it appears nowhere in the theory

Following your logic, can I ask the question is the theory of evolution incomplete because it does not explain gravity?

Evolution is linked to gravity in about the same way as QM, I mean gravity acts on objects that are part of the theories doesn't it.


That is your personal view but it is also just as likely wrong and both theories could be perfectly correct and simply merge in a currently not understood way

I have no problem with you calling it Quantum Gravity just don't claim such a thing is Quantum Mechanics. You can say it contains parts of QM or is based on QM etc but as you intimated you have to break something in QM for it to work.

So again I have given you the answer QM does not answer everything in the universe which was your rather stupid claim that I believed. I think it is entirely likely based on the current state of science that gravity has nothing to do with QM. String theory is/was the only contender to join the two theories and that has run into experimental failings thus far.

The problem is the questions Bill S is asking are not shallow end of the pool questions. Using your analogy it is like going out into the middle of the Atlantic ocean and say teach me how to swim just like the shallow end of a pool

I know of no science communicator who can get answers to the questions Bill S is asking without Bill S needing to learn more. If you know someone please recommend them to him.

In the next 6 months there will be some rather interesting developments on black holes and gravity as a huge gas cloud called "G2" is heading straight for the black hole at the centre of the milky way. A lot of observatories will be watching what happens with keen interest and there is a possibility of new discoveries to do with black holes and perhaps his questions will be more direct observation answerable but it is a hope not a guarantee.

But you are the one that started spouting about QM in the middle of a discussion of GR. So it appears that you think QM is an integral part of GR.

I was discussing GR with Bill S. when you came along with your attempts to "educate" Bill S. on QM subjects. Since what we were discussing was specifically related to the usual analogy between GR and a bowling ball on an elastic sheet I don't see what relevance your references to QM had to do with the discussion. They implied, as usual, that you are still on your QM is master kick.


And no decent teacher tries to teach a student the advanced material without first leading him/her through the preliminary steps. If Bill S. needs to know more he needs to be given the basic knowledge that he needs to understand the advanced material. In other words work through his questions, and help him understand, don't just say here study all this advanced material and then you will be able to answer the question yourself.

I have been trying to help Bill S. see just how the bowling ball analogy fails by taking his questions one at a time, as he brings them up. I don't think he needs to have a complete understanding of either QM or GR, he just wants some help in figuring out how to view them. I doubt if he is interested in getting a PHD at his age.

Bill Gill

With regard to the swimming analogy: I am self taught, and my first “lesson” came when, as a child, I fell overboard at sea; real deep end stuff.

Orac, I have probably given the wrong impression about links and background learning. The problem arises when I ask a question, you give a link that at first sight seems unconnected, and add a cryptic comment. I look at the link and the comment and think “this must somehow relate to my question, but I don’t know how; I’ll come back to it when I have time.” Chances are I never get back to it. Perhaps a link with a clear indication as to how it is relevant would be most valuable.

It may be that you suspect some of my questions are deeper than they are. For example, Bill's contributions to the gravity/force/energy provided the impetus for me to sort out the thoughts that were responsible for my OP.

Again another blatant lie ... at least have the decency to go back and read what was written.

Basically you have got your bee in a bonnet with me (like your 3rd world science mag reader mate) and are now getting continually caught out because you are inserting lies and claiming I said them

So we are clear I am explicitly saying QM has nothing to do with GR. You can however show they are mathematically consistent with certain assumptions which was done as part of string theory research.

You are the one who keeps bringing up this place holder you want to call "Quantum Gravity" whatever that pink elephant is. Mysteriously you believe in it but are unable to enlighten us as to what and how it is going to work.


The problem is you aren't helping him you are telling him complete garbage by repeating science media trash that is either so far out of date or just plain wrong. Unfortunately the quality of most of the "science writers" is very topical this week with many launching broadsides at them with them promoting complete crackpot low quality papers that struggled to get published and many suggested should not have been.

So let me be clear as it stands today there is no known connection at all between gravity and QM. String theory was and remains the only player that can encompass that connection and so for most scientists the possible connection relies on their belief in string theory. There are no observations and no experimental results that can seperate the two theories.

This week the current record for the sensitivity for looking for a difference was done here is the layman write-up
http://phys.org/news/2015-02-michelson-morley-electrons-quantum-information-techniques-explore.html

The short version memo is QM/GR remain consistent down to that level which is now the new limit they have been tested.

I have no issue with that and as I said Bill G's initial answers were also correct.

As we had discussed the only constant you have to reference everything is energy, I even gave you the steps to follow


Did you manage to make the connections and see the problem?

This is sort of why I took exception to Bill G and his lies and rubbish because I actually tried my hardest to keep QM out of it.

Hint to problem as quoted in article:



If still stuck read the Newtonian section in this and we will discuss:
http://en.wikipedia.org/wiki/Friedmann–Lemaître–Robertson–Walker_metric

I am hoping it will help you seeing universe inflation shown in purely classical newtonian terms.

I have never claimed that you did say it. I do claim that everytime we start a discussion of GR you bring in QM, even though it doesn't have anything to do with the particular application of GR that we are discussing.

I agree that Quantum Gravity is a place holder. It happens that the term makes an excellent place holder.


Good, then tell us what is the 'correct' garbage. I have not seen anything new that changes what I have been saying.

And of course for a lot of people string theory is highly suspect. So I agree that QM and GR are separate. They do work together in that effects of one will affect the other. For example GR tells us how clumps of matter formed in the early universe. QM tells us how those clumps of matter became stars.


I'm not sure just how that consistency leads to anything different from what I have been saying. Yes, there appear to be universal laws that are active in both QM and GR, but that doesn't change anything I have said about the special case of GR concerning a bowling ball on an elastic sheet.

Then you throw in Planck's constant. I'm not sure what this has to do with the bowling ball. Nothing I said approaches the Planck level.

Then you say there is a problem and ask Bill S. and by reference me and all of our other readers to figure it out. We can't do that. You need to explicitly explain that for all of us dumb stupid people that believe that scientific knowledge evolves but that the basics stay the same, unless you have a major break through like Einstein.

And then down at the end you bring in the inflationary universe. I can think of nothing that that has to do with the OP, which was about the bowling ball and the elastic sheet.

So Orac, if you are going to comment, please provide clear concise statements that answer the questions asked. Don't go off on tangents that just seem to show that you aren't really interested in telling us how the world works, you just want to show off how smart you are.

Bill Gill

Well then you might try and work it out hey, who knows you may learn something ... this is all 1905 to 1930 stuff.

So lets give the history lesson shall we.

1905 Einstein connects energies via the PhotoElectric effect.
1915 Einstein publishes General Relativity
1920-1930 People actually try to calculate if the energy is compatible between those two

We name the calc after the 4 people who independently calculated it in different ways. It is called then Friedmann–Lemaître–Robertson–Walker_metric.

It is the very thing that Bill S is asking does the energy conserve and you with you layman basic examples are trying to answer but without being able to put any equations together.

You will note it covers a static universe, an expanding universe and a contracting universe and shows the energy relationships between them according tor your pet GR.

I believe that is the bit Bill S was trying to understand was it not?

You will also note there are some assumptions to the calculation which Bill S may or may not decide are valid I leave it up to him.

The assumptions are

1.) The universe has homogeneity or so called isotropy
2.) Energy has negative pressure, equal in magnitude to its (positive) energy density

Number 1 you will be probably able to talk your way around. Number 2 is going to give you some problems so I would like you to deal with that please. Maybe scientists randomly made that up so perhaps you would enlighten us how that bit works.

I know you don't understand the connections and your layman ignorance caught you out yet again

This stuff is stock standard cosmology Bill G, pretty much as main stream as you can get

Ok, now you have told us all the problems we have. No explain them to us in words that we can understand. And also explain clearly how they affect my explanation of the bowling ball on the rubber sheet Bill S. and I have been discussing.

Bill Gill

Bill S was asking about deformation energy and in that he at least realized the rubber sheet example is very very limited. If either of you had turned the problem to a bowling ball on a water bed at least conceptually you would be closer to the reality.

Basically you might as well discuss the whole thing properly at that point ... oh but this is SAGG I forgot sorry.

So yeah I apoligize for trying to discuss any actual real world physics with you ... my mistake won't happen again and I will leave you with it

If you don't know how to explain what you claim to know why don't you just admit it?

Bill Gill

LOL you got me Bill I don't know your version of science at all and my byline admits everything doesn't it, I put it on every post. Perhaps you would like me to add some more to it

Seriously I think you mistake me for someone who cares what you think and that is a bit like worrying what Marosz thinks. Perhaps go for the appeal to the audience that is what those who need a crutch usually do next. I am sure there is a huge audience out there hanging off your every thought, Marosz is sure of it.

You really don't read anything I write and distort and lie what is actually said anyhow, so seriously why would I waste my time explaining anything to you. I am just really enjoying you explaining the real science my little "Bill in the box" and I am learning so much

Now back on topic you need to explain to Bill S how the energy pressure thing works as it really is the basis of his pondering about deforming space energy.

So Energy has negative pressure, equal in magnitude to its (positive) energy density explain the "real science" to us please

As you say I know nothing of this stuff so I really can't help or offer any hints

I'm willing to learn, if you will explain it in simple terms that I can understand.

Bill Gill

I assume you are making a distinction between "energy pressure" and "pressure energy". If not, there is a vast amount of research to do; if so, can you point in an appropriate direction?

Nice to see someone thinking on this forum so lets first do the standard science.

So the standard GR version basically has at the bottom of it the concept of dark energy (this is the hole that Bill and Rede fell down), you can't believe in GR but not in dark energy they are joined at the hip

There are two ways that it is conceptually taught as either a cosmological constant or as quintessence depending on the scientist you ask and what they believe/promote

The cosmological constant version goes that there is a cost to energize a portion of space. Why the cost exists involves a bit of hand waving and saying that is just the way it is. The key criteria it sets out are

1.) The vacuum energy density is constant because there is nothing for it to depend on. This fits back to the original premise of uniformity of all space.

2.) Using classical thermodynamics and assuming the constant exists and you consider the volume of space is finite. A change in volume (dV) requires work done equal to a change of energy E = -P*dV, where P is the pressure, E being energy. However as your space volume has increased and you assumed a cosmological constant for space then the total energy must have increased. So the conclusion is that P must in fact be negative to give you a positive energy value for (E) ... We don't allow negative energy in classic physics !!!!!

Now there are a number of problems in all that, some you will immediately see others are not so obvious. One important not so obvious problems is the cosmic constant is incompatible with the standard model at low matter denisities, how problematic this is depends on your faith in the standard model.

If the cosmological constant is your thing then the favoured model is called Lambda-CDM.

Your second choice quintessence conjectures a fifth unknown scalar force which is varying slightly over time. Paul J. Steinhard's cornerstone work on the idea is technical but should be somewhat understandable by even a layman

http://physics.princeton.edu/~steinh/steinhardt.pdf

Scalar fields are predicted by the standard model and string theory but there are problems with renormalization of a slow changing scalar field. Which set of problems is worse well that is in the eye of the beholder.

If you get excited by quintessence you may care to look at the most favoured model at the moment called slow rolling inflation.


So how do you distinguish between the two ... well in short detailed and prolonged measurement of the fundemental forces

We weren't discussing the implementation of GR. We were discussing the analogy of a bowling ball on an elastic sheet. We never got any place close to dark energy, just the one simple analogy and how it worked. The only hole I fell down was the one created by the ball. And of course your farfetched claims about what I am saying.


That's what all science is. All science, including QM basically is a description of "how it is". It doesn't tell us anything about why. Planck in particular wasn't trying to invent a whole new branch of physics. He was just making up something that made it work. I don't think he even really believed in it as anything other than a gimmick.

Bill Gill

So what is it an analogy of .... this should be interesting

You may also care to note Bill S asked specifically how it worked under GR but obviously you don't bother reading what he writes either

The fact you didn't realize you had to introduce dark energy speaks volumes of your ability to answer the question asked. I am waiting for the "Bill in the box" corrections to my undoubtedly wrong views on Dark Energy


Ridiculous claims about what someone is saying, do you find it irritating ... you never do it to me do you


That may be how "Bill in the box" science works. I guess I should be fair and ask do you believe this is a standard science consensus view?

Perhaps a hint of a warning from janitors who definitely don't practice "Bill in the box" science and it is usually expressed in a very precise phrase ..... Correlation does not imply causation

Bill S with his latin would recognize it as "cum hoc ergo propter hoc".

I assume that you are saying that QM does indeed tell us why things are the way they are. I believe that QM is a set of equations that can be used to determine what will happen under certain circumstances. So given that you can tell me why, for example, entanglement happens. I know that the equations tell us that it will happen, but I don't know where in the equations we can find WHY. As far as I know modern science is descriptive. It doesn't go into why things happen, just how they happen.

Bill Gill

Ummmm if you bothered to read anything I ever said that is pretty much what I dislike about QM in it's current form (according to the science media) if we are forced to throw out string theory.

So yes to what you said and I pretty much complain that in it's current form QM is going down the GR/dark energy path. You may call that a janitorial criticism of both and the process

I don't feel compelled to believe everything that brain dead science media likes to propel as some sort of agreed take on things and which are bordering on crazy anti-science garbage. You can call it my janitorial license to do so and I can tell you I am not alone in my criticism.

You still never told me what the rubber sheet and ball was an analogy of ... perhaps worst ever Newtonian gravity model

Anyhow lets see if Bill S is any closer to his answer.

Well, now you have me completely bumfoozled. First you are saying that our bowling ball on a rubber sheet analogy for GR is incomplete because we don't include QM, now you say that QM is bad for some strange reason.

String Theory is probably going away some day just because nobody can make it give us any kind of a good match to what we see around us.

The bowling ball on a rubber sheet is the widely used analogy for GR as I said in the first paragraph above. That was part of Bill S' question at the start of the thread. So I don't see why you think I need to explain it to you again. It is after all what we started off talking about.

You still haven't answered my question about what dark energy has to do with the bowling ball. As far as I know dark energy wouldn't apply to the static case of the bowling ball. Dark energy would apply to dynamic systems, such as the universe. The bowling ball analogy is just a way for people to visualize the warping of space by a mass.

Bill Gill

Perhaps go back and read .. can you read Bill?

I never mentioned QM at all, in fact my only mention of it all was to tell, Bill S to ignore it

You really need to actually start reading what people say because I am starting to think you have signs of an age problem.


And there in lies your problem ... you don't get it


Really so dark energy only applies to a dynamic universe ... wow that is an amazing claim

Perhaps think about the positive pressure example Bill and an inflated car tyre and the car weight sitting on it .... or perhaps even a bowling ball

Shall I give you a historic hint:http://en.wikipedia.org/wiki/Static_universe
Einstein's static universe is closed (i.e. has hyperspherical topology and positive spatial curvature), and contains uniform dust and a positive cosmological constant


That is because the rubber sheet provides elasticity, perhaps think about what provides the elasticity in space Bill. We don't really call it elasticity but it has the same deform behaviour (using Bill S words and idea) and something has to snap the deformation back which Bill S was wondering about and even if a partial deformation could remain. We give the thing doing this a name under GR, want to guess what it is?

Lets see if the penny drops yet. The incompleteness had nothing to do with QM ... do I need to repeat that 20 times so it sticks ... wait let me make it red.

However you left something else out, a name we shall not speak apparently

So your question is under GR the mere act of putting energy and/or matter into a bit of space (static or moving) does something ... what is it?

OK, I give up. You really don't see that Bill S. had a simple question about the analogy of a bowling ball on a rubber sheet. And that the problem was that it was a simple analogy. I answered his questions about it based on the fact that it is an analogy and analogies are always imperfect. But the bowling ball analogy is just that and it is an extremely simplified analogy. It does not embody the whole of GR. GR is much more complex than the analogy. The bowling ball is a simple analogy that allows somebody to envision how space is deformed by a mass. That is ALL it does. It doesn't get into any of the other aspects of GR. You, in your usual manner, have tried to invest this simple analogy with a huge load of mystery that only you can understand.

Bill Gill

Bill S's question was asking the question of deformation of spacetime and while your analogy setup may provide basic child similarities it can't and doesn't answer the questions you need to deal with the issue properly and that means talking about dark energy and Stress–energy-tensors.

GR defines that putting energy and/or matter in any form into space creates gravity and is opposed by a repulsive dark energy force ... that is what GR says and how it works.

So your static bowling ball moving or not is opposed by dark energy just by the fact it exists as a clump of matter. You never got that originally and you still didn't get that in your answer above in fact you insist the opposite

In some ways gravity creates dark energy but I have edited and steered away from that terminology because it can lead to some very wrong conclusions and so I have used the term opposed being more in line with classical physics.

Bonus point question: A photon contains energy and exists in spacetime does it create gravity under GR, even though it is mass less

My first thought was "yes", but then I thought "Although energy can, seemingly, create gravity; isn't it more to do with the stress-energy tensor, than just energy?"

Tensors are a bit mathematical for me, but I suspect the answer might be "no", because there are lots of components to the S-E T and I don't think they are all appropriate to a photon.

Another thought that has just struck me is, would we need a quantum theory of gravity to answer that question?

We have a bonus question winner ... and yes you got all the various components and pass with an A+.

I did limit the question specifically to GR for a reason

So the answer is sort of conditionally yes under GR although as you said you can sort of argue condition exemptions etc. One of the problems is under GR there are many possible distinct definitions of the gravitational stress–energy–momentum pseudotensor because it is a very mathematical process which you also got. So the GR answer you derive may actually hinge on what definition you selected and it's funny watching two scientists go at it with different definitions

You got the final part that the actual true answer probably needs a full theory of gravity, so at the moment all we can say is probably yes without the full theory or an experimental result.

So you got every component that the question poses and did better than some scientists I have seen tackle the question. It is a really challenging question that usually sets of furious debate and is really fun to ask a particular group of physicists

Now I should say my GR is not up to date and it really isn't my thing and this may be a really interesting question to put to Ethan Siegel to get a really modern view on this.