41

Flat Earth Theory / Re: Question about the Vomit Comet

« on: April 29, 2021, 01:28:26 PM »

The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.

Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

I entirely agree - I wasn't bringing relativity into this. I'm simply talking about an inertial reference frame - a frame of reference, or datum, that is not accelerating. So the surface of our earth is a good inertial reference point (ignoring very small error due to rotation and the centripetal acceleration towards the sun - barely measurable). You could also use a vehicle travelling at constant speed. To borrow from another thread, you and I could play table tennis on a moving bullet train, and the ball would fly just as it would if we were at rest in a station. To calculate the ball's motion we could choose the train as a reference point - a valid choice, as it is inertial (ie non accelerating),and a wise one, as it keeps things simple - we measure all velocities etc with respect to the train. We could if wished, choose the earth, but then things get complex, because all the velocities would have the motion of the train superimposed on them, meaning a negative velocity with respect to the train might still be positive with respect to the earth.

But it all breaks down if the train accelerates. If you hit the ball to me and the train brakes suddenly, then the motion of the ball with respect to the train will not be what we would expect at all - we would have to choose the earth as a datum, or perhaps compensate for the acceleration in our calculations - engineers sometimes use d'Alembert forces to do this. You sometimes see it being done with circular motion - they add a 'centrifugal' d'Alembert force, even though no such thing exists, to change an accelerating reference frame into an inertial one.

If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".
doesn't mean that a "falling object" is accelerated by UA, what does it mean?

Again, the FEers are sort of, oddly correct here. The whole thing is nonsense, clearly, but as a thought exercise it does work.

Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work. So we have to imagine ourselves outside the earth, stationary, watching it accelerate past our fixed datum point. The earth is accelerating 'up' at 1g. The earth's atmosphere will eventually achieve a steady state whereby it ends up with a pressure/density gradient just like our atmosphere does on our beautiful, globe-shaped earth. Once stabilised in that state, it too will accelerate at 1g - every small 'parcel' of air will experience a net 'mg' force pushing it up. So we have a planet and an atmosphere accelerating upwards at 1g. If you then drop a ball from a hot air balloon or similar, the ball will initially be stationary with respect to the balloon, so it will have whatever velocity with respect to us observing that the earth/atmosphere/balloon did at the point of release. But it will retain that velocity, while the atmosphere and balloon etc keep accelerating, and so will appear to 'fall' from our perspective. As it falls it will start to experience a force, increasing with the square of the velocity difference, as the air rushes past it. At some point the drag force will reach mg, at which point the ball's upward acceleration will equal that of earth/atmosphere/balloon. However, it will retain a constant velocity difference. With respect to the earth's surface it is falling at terminal velocity. With respect to us, it is accelerating upwards at the same rate as the earth/atmosphere/balloon, but is at a slightly lower velocity. So the earth might be going at 1000m/s, and our ball might be going at 970m/s, with each adding 9.8m/s to their speed every second - the ball has a terminal velocity of 30m/s.

Note: none of the above obviates the numerous issues with the UA model, or indeed the many obvious flaws in the FE model generally.

Would quibble with a couple of points,  but none are relevant to this discussion.  The important point is that you acknowledge that an object in the atmosphere of an earth accelerating upwards, will also accelerate up. And it will accelerate up at 1g.

Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work.

I’m not using Newtonian maths.  In relativity, the worldline of an accelerating earth (or anything accelerating at relativistic speeds) will be a hyperbola. The worldline of an an object accelerating at less than relativistic speed will not be a hyperbola, but it will be diagonal.  The worldline of an object that is not accelerating will follow tbe straightest possible path through spacetime.  In flat space spacetime, the worldline will be vertical, as an object at rest is moving through time but not through space. In curved space time, it will follow the curve of time, but won’t travel in space.

Frame of reference is irrelevant.  First of all, the occupants in the plane are in the same frame of reference as the plane, so if the plane is accelerating in its own frame, the occupants will experience that acceleration.  But more importantly acceleration is not relative .  If something is accelerating, it has a force on it.  Changing frames of reference doesn’t make that force go away.  It’s either there or it isn’t and objects and if its there, people being accelerated will experience the effects of the acceleration.  The perception of the force and the resulting velocities may be different in a different frame, but the fact of the force and the fact of acceleration doesn’t change.  Something is either accelerating due to a force or its not.  That is an absolute. No change in frame of reference changes that.  Clear enough?

So if, no matter what frame of reference you are in, the atmosphere is accelerating the plane up, at 1g, and is the only force on the plane how is it that the floor of the plane is not pushed against the occupants?

42

Flat Earth Theory / Re: Question about the Vomit Comet

« on: April 28, 2021, 11:04:43 PM »

A question for anyone who can answer, but from an FE would be nice..

If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".

doesn't mean that a "falling object" is accelerated by UA, what does it mean?

43

Flat Earth Theory / Re: Question about the Vomit Comet

« on: April 28, 2021, 10:38:52 PM »

The plane and the person are NOT being accelerated by UA.

Well, like i said, that seems to be thrust of the issue .  The wiki implies that the plane and the person would be accelerated by UA.  It would be nice if an FEr would clarify.

The wiki defines terminal velocity as When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.  And note that it's in the "universal acceleration" section of the wiki.  To me that implies that under UA, a "falling object" is being accelerated.

I want to clarify this statement.

With that in place, all the maths makes sense

The maths only make sense if you are considering unaccelerated motion. GR divides all motion into geodetic, unaccelerated motion that is traveling along the straightest possible path under no force and non-geodetic, accelerated motion not along the straightest possible path and under a force.

No change of perspective, manipulation of coordinates or maths can change one into the other.  Geodetic motion will always have the straightest possible worldline, non-geodetic will not.  If you plot the worldline of an earth that is not under any force, you will get the straightest possible path through spacetime. If you plot the worldline of an earth that is under acceleration by UA, you will get something other than the straightest possible line.

That is what the maths show according to GR. An earth under acceleration will follow a hyperbola. An earth not under acceleration will not.

44

Flat Earth Theory / Re: Question about the Vomit Comet

« on: April 28, 2021, 08:50:41 PM »

The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.

Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

So FEers are correct (for a change!) on this one - were we to exist on a UA/FE world, it would be indistinguishable from our current environment.

Indistinguishable, that is, apart from the stars and planets rotating beautifully around our celestial poles, and the massive discrepancy between observed distances between known points, and all the many other things that, aside from the actual footage of our beautiful round earth viewed from afar, clearly point to it being globe shaped.

A lot of Rers seem to buy into this notion as much as the Fers and its simply not true. I think it come from the belief that the EP, and relativity in general makes all motion relative. It doesn’t, It only makes unaccelerated motion relative.  Which overall, accounts for a small portion of the motion we see in real life.

So if the occupants in the Vomit Comet were being accelerated by the UA force, they’d know it, just like the guy in the closed box floating around in space.  If the floor came up and hit him or the he hit the floor, either way he knows he’s being accelerated.  He may not know why, but he knows he is.

Terminal velocity, in that context, would be achieved when the drag force acting on the object was equal to mg - exactly the same as on the inertial 'normal' planet earth.

The difference is If terminal velocity is defined as “when the falling object is accelerating at the same rate as the earth”...then the falling object is still accelerating, which means its velocity continues to increase.  As opposed to the RE/gravity concept of terminal velocity… when an object is no longer accelerating and its velocity stops increasing. You’d have to use two different formulas to determine those two very different things.

Anyway, back to my original question.  It seems like it boils down to whether or not the UA force would cause the atmosphere to accelerate and the plane along with it.

45

Flat Earth Theory / Re: Question about the Vomit Comet

« on: April 28, 2021, 05:48:25 PM »

I think the point you are missing is that the UA 'force' is deemed to only act on the earth - everything else is then pushed up by the earth. You are correct, in that if UA pushed on everything, then the parabolic flight profile wouldn't work

.

Well, maybe it is the UA/FE model I don't understand.  But from other discussions, mostly about skydiving, I thought that the UA force accelerated the atmosphere along with the earth and that anything in the atmosphere accelerates along with it.  And that the reason that the earth eventually "catches up" is because drag slows down the acceleration of whatever is in the atmosphere.  It is accelerating at a slower rate, so eventually the earth is able to cover the distance between them.

The wiki defines terminal velocity as ‘When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.’

A “falling object” is being accelerated...by something other than gravity.  The Vomit Comet is a “falling object” what’s accelerating it? The whole concept of terminal velocity in UA makes it impossible to use the same formula in UA than gravity, but that's a different thread.

All the things you might have actual experience with, like rocks, plants, animals, water, air, planes, etc. aren't apparently affected, for some mysterious reason. Otherwise, you'd get rocks that hover when they're dropped, something which I don't recall ever seeing.

The UA force doesn’t work directly on thing on the surface of the earth, but it does effect them.  Otherwise, the “pinning force” that is described in the wiki wouldn’t be necessary.  That’s their explanation for why we don’t see things hover.

Go back to the often used analogy used to describe the EP.  The closed box has no other force on it other than it is being accelerated up by some force and that causes whatever is in the box to become  pinned to the floor.

A plane in parabolic flight is the equivalent of the closed box.  It has no other force on it other than it is being accelerated up by some force.  If that force causes the person in the box (who isn’t being directly accelerated) to be pinned to the floor, the same thing should happen to people in the plane, who also aren’t directly effected by the accelerating force.


EDIT: Another thing to consider is that even if the plane is neither accelerating upn or accelerating down, its going to take a lot less than the 45 seconds or so that the plane is in freefall before an earth accelerating up at 1g to slams into it.

46

Flat Earth Theory / Re: Question about the Vomit Comet

« on: April 28, 2021, 02:58:51 PM »

In essence, UA is just another form of drag.  If thrust can overcome drag, there's no reason to believe it doesn't also overcome UA.

I was thinking more like UA is thrust...that you can never adjust or turn off like you can a rocket engine.  In order to be in free fall, thrust and drag must be equal.  Since you can't adjust the thrust UA causes, how do you equalize the drag so that the plane is in freefall?

Don't know enough about how it works, which is why I asked.

47

Flat Earth Theory / Question about the Vomit Comet

« on: April 27, 2021, 09:57:51 PM »

Hoping one of you good people who are familiar with how the Vomit Comet works can clear something up for me.

My understanding is that during parabolic motion, thrust and drag cancel each other out and lift is reduced to zero because of the angle. That leaves just gravity working on the plane and since the plane and the occupants are falling together, there is a sensation of weightlessness.

I don't see how this could work with FE/UA.  Without any other forces to counteract it, the UA force should continue to accelerate the plane up, pushing the floor of the plane up and creating the sensation of weight.

Essentially, no different than our friend in the enclosed rocket ship that can't tell if he's being accelerated up or gravity is pulling him down.

48

Flat Earth Investigations / Re: Cavendish experiment

« on: April 27, 2021, 02:00:07 PM »

Incorrect. The entire article is about how gravity is difficult to measure and how they have been getting different results. He said that "This has, however, been VERY difficult to prove! Measurements of the gravitational constant over the past 200 years have been erratic.". Not 'can', not 'sometimes', he said 'have been'. I would suggest that you  try to present something that supports your case, rather than plugging your ears and pretending that the author said something else and is being misquoted.

What difference does it make if the measurements aren't exact?  The fact that it can be measured at all is proof of its existence.

If lack of consistency in the measurements is a problem, it is a bigger one for FE/UA.  RE embraces the idea that the gravitational force can vary, FE/UA rejects the idea.

49

Flat Earth Investigations / Re: Cavendish experiment

« on: April 26, 2021, 07:40:13 PM »

It has to do with a earth being stationary. If you travel 9 m/s, your kinetic energy is 8.100 joule (at 200 kg), at 10 m/s, it's 10.000 joule, and at 11 m/s, it's 12.100 Joules. Now if you move at 10 m/s, and your environment (earth) does so too, what they claim with the spheircal earth, you would perceive as standing still. But it would cost more energy to change speed in one direction, than that it would in the other direction.

I think Bob beat me to it. Still not sure I understand what you are getting at, but it seems like you are missing the fact that because velocity is relative, so it kinetic energy.  If it seems like it takes it takes more energy to change speed in one direction, than in the other, then its because you are using two different reference frames.

50

Flat Earth Investigations / Re: Cavendish experiment

« on: April 26, 2021, 05:21:52 PM »

Now the second argument is about kinetic energy ((1/2)mv^2, m being mass, and v being velocity). If you are 200 kg and go 10m/s steady state together with your environment (this is just an example to make calculation easy), then, to change speed with 1 m/s in one direction would take 2100 joules whereas changing speed by 1 m/s in the other direction would take 1900 joules. (Huh? nobody ever could explain me this. If you're a physicists reading this, please explain).

I don't understand the question.  What do you mean by "change speed with 1/ms in one direction"? And what does the question have to do with the shape of the earth?

51

Flat Earth Theory / Re: Simple Experiments

« on: April 25, 2021, 03:17:08 AM »

That flips the discussion on its head

Not really. Conceding that Gravity/RE can work doesn’t solve the problem of how UA/FE needs to cherry pick from competing concepts to argue that what we see in reality is UA and not gravity.

If what we see in reality is UA, then gravity cannot be the force that causes the downward acceleration of objects.  If gravity causes it, then it is impossible that UA causes it.

The easiest way to dismiss the idea that gravity is the force that causes downward acceleration is to reject the idea that it is a force at all.

52

Flat Earth Theory / Re: Simple Experiments

« on: April 24, 2021, 04:14:59 PM »

Could you perhaps show an example of FE'ers wanting to say that? Keep in mind that your current conversation is a bunch of RE'ers unable to agree on the fundamentals of the model they claim to support - FE'ers have long abandoned this mess.

Point well taken.  I don't recall ever seeing it explicitly stated that way.  However, I would argue that is the only logical reason for rejecting the idea that gravity is a "force".  If gravity is a force, then the motion of falling objects can be contributed to gravity and there is no reason to come up with UA as an alternative theory to explain why things fall.

53

Flat Earth Theory / Re: what is your weight?

« on: April 24, 2021, 03:53:03 PM »

What we perceive as weight is nothing more than the normal force pushing up.

Disclaimer: I'm sticking with Newtonian concepts of gravity/RE concepts to avoid confusion.

On an RE with gravity, gravity is pulling you down onto the ground.  According to the action reaction principle, the force of your feet pushing on the ground causes the ground to push back up.  That's what you perceive  as your weight.

As long as you are perfectly perpendicular to the ground, the two forces will be equal.  The force of gravity pulling you down onto the ground will be equal to the force pushing you back up.  As long as those two forces are equal you remain stationary.

You don't "fly off" at the equator, because no matter where you are on the earth, gravity and the normal force will "equalize" in response to one another, keeping you on the ground.

If you aren't perfectly perpendicular, and the gravitational force and normal force aren't exactly equal, you don't fly off, but you will fall down, again equalizing the two forces, keeping you in place.

54

Flat Earth Theory / Re: Simple Experiments

« on: April 24, 2021, 02:59:01 PM »

Yes, but equivalence allows acceleration and gravity to cause motion in two different ways in the two differing views.

Gravity doesn’t cause motion in GR. That's where the disconnect is. In GR gravity isn’t a force and only a force can cause motion.  FE wants to say, “In GR gravity isn’t a force, therefore in GR gravity doesn’t cause motion.”  but GR doesn’t say that gravity causes motion.  They are disputing a conclusion that GR doesn’t make. 

Does FE state that the effect of acceleration is the warping of spacetime?  I don't believe it does but admittedly don't know.

Tom I know rejects it, but I don’t think I’ve ever seen an “official position”.  Logically, they have to reject it (so at least Tom is consistent in that) because if acceleration warps space time then the EP as justification for UA goes out the window (no pun intended).  It allows for not just an alternate, but a better explanation for gravity than UA.

If you accept that acceleration warps spacetime and maintain consistency between Newtonian and GR concepts, this is where a coherent argument leads...acceleration causes spacetime warp, acceleration and gravity are the same thing, therefore, gravity is the warping of spacetime, not some force that accelerates the earth up.

IF the earth were flat and accelerating upwards due to UA the water and bottle would behave exactly the same way as under GR.  Which one happens to be true is irrelevant to the test.

Since the EP doesn’t apply, there is no reason to assume that, and other reasons to assume that it would not be the case.

55

Flat Earth Theory / Re: Simple Experiments

« on: April 23, 2021, 04:00:00 PM »

Isn't it that force in UA that would create the water pressure? The bottle is accelerating up, so water in it which would naturally stay at rest is pushed to the bottom of the bottle by the bottom of the bottle accelerating upwards

If the bottom of the bottle is accelerating up, it wouldn't push the water to the bottom of the bottle. It would push it up to the top.  Like I said, that would create water pressure and explain the results of the demonstration.

But it is also contrary to everything we observe about how water behaves in any other circumstance.  On earth we observe that water's, natural motion downward.

56

Flat Earth Theory / Re: Simple Experiments

« on: April 23, 2021, 03:49:59 PM »

You've got to admit that on the surface curvy space time is as absurd a concept as bendy light.

I disagree with that.  Curved spacetime is validated by Einstein's field equations (not to mention experimental evidence).  It works exactly as predicted by the field equations.  As far as I know, there are no equations that can be used to validate bendy light.

No contradiction.  Equivalence doesn't mean my force equals your force.  Equivalence means my force equals your spacetime curve.

What the equivalence between acceleration and gravity means is that they produce the same effect.  If the effect of acceleration is motion, then the effect of gravity is motion.  If the effect of acceleration is the warping of spacetime, then the effect of gravity is the warping of spacetime.

Your response just makes my point.  Use the Newtonian definition of force to explain why gravity is not a force in GR.

Fers claim that gravity is not a force in GR, but completely ignore the reasons why.  Accept the conclusion, but not the reasoning that leads to the conclusion.  Does that make sense to you?

Not only is that cherry picking, its wanting to eat your cherries and have them too.

57

Flat Earth Theory / Re: Simple Experiments

« on: April 23, 2021, 03:28:41 PM »

But the point is as soon as you let go of the bottle the force you were applying on it stops, no force is acting so what would make the water leak out of the bottle?

That’s the million $ question.  What force acts on the bottle while you were holding that does not act on it when you you let go?

The only thing that comes to my mind is water pressure.  The real reason the water stops flowing when there is no gravity is because without gravity, there is no water pressure.  So I suppose you could say that without acceleration there is no water pressure.  But that’s just another way of saying the EP applies and raises a whole bunch of other questions in the process.  Not necessarily saying there aren’t answers to those questions, but its just another example of how every answer raises another question and every solution causes another problem when one tries to understand UA.

So if we go with the water pressure answer, we have to ask what caused the water pressure in the bottle when you were holding it? On RE water pressure is created because of water’s natural motion to “go down” aka “seek it’s own level”...because of gravity.  Without gravity, with UA, is water’s natural motion up?  That would solve the problem of what causes the water pressure in the bottle why you are holding it...but raises new questions about how we observe the behavior of water in any other situation.

If water’s natural motion is up, it doesn’t “seek its own level” and there goes an argument for the flat earth.

See what I mean?  It’s just one big rabbit hole.  Fers want to waive the EP flag like a magic wand and pretend that it solves all the problems with UA, but that is far from the case.

58

Flat Earth Theory / Re: Simple Experiments

« on: April 23, 2021, 01:30:54 PM »

It is under constant acceleration. If you ignore air resistance and terminal velocity, it's accelerating constantly at 9.8m/s2 towards the earth, no?

It is under constant acceleration. If you ignore air resistance and terminal velocity, it's accelerating constantly at 9.8m/s2 towards the earth, no?

Then you are conceding that the water bottle is in a gravitational field, and UA can't account for the water not  flowing.  Once you determine that the bottle is accelerating in a gravitational field, you eliminate UA as a cause.   

For the EP to apply, you need to be able to say that it could be true that the water is not flowing because of UA and it could also be true that water is not flowing because of gravity. If the bottle is at rest, you can say that.  But in order for the bottle to be at rest in a gravitational field, it has to be supported by something.

EDIT: Just in case the dots are connecting for some people...since the bottle isn't supported, it is accelerating at 9.8m/s2 and we can conclude that UA is not responsible for the water not flowing.

59

Flat Earth Theory / Re: Simple Experiments

« on: April 23, 2021, 12:10:24 PM »

So let's take UA under GR.  UA says earth accelerating upward.  Bottle and water without holes aren't allowed to follow their geodesic because the force of the person holding the bottle is causing them to both accelerate upwards and the impermeability of the bottle is the force that prevents the water from following its geodesic.  With holes, the force of impermeability is removed allowing the water to follow its geodesic until the time that the upwardly accelerating earth applies the force to stop it.  When the bottle is released, both water and bottle are now allow to travel the same geodesic until the upwardly accelerating earth meets them.  Again, reads an awful lot like old school physics.  Either way, the bottle and water behave exactly the same in both cases.

The concept of geodisics only apply in the context of curved spaces.  FE/UA (as far as I understand) rejects the idea that spacetime is curved.

But your response is interesting in that it is exactly how FE will cherry pick certain concepts from both Newtonian physics and GR and try to marry them into one "theory".  Some things, that's not a problem.  Others end up causing obvious contradictions in their own theory.

FErs love to point out that under GR gravity is not a force. Somehow that supports FE/UA. Then they use the EP to explain how UA works as a "force".  Do you see the contradiction?

If gravity and acceleration are equivalent and gravity is not a force, then neither is acceleration.  There can't be any "force" pushing the earth.  EP doesn't make UA possible, it makes it impossible. 

60

Flat Earth Theory / Re: Simple Experiments

« on: April 22, 2021, 11:16:40 PM »

 

In RE, gravity is still acting on both the bottle and the water equally while it is in freefall.  If it weren't, the bottle and water would cease to fall.

I would ask what part of GR don't you understand, but apparently its all of it.