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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Le Repteux on 22/09/2018 15:25:01

Title: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 22/09/2018 15:25:01
Here is wiki on tidal acceleration: (https://en.wikipedia.org/wiki/Tidal_acceleration)
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Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon), and the primary planet that it orbits (e.g. Earth). The acceleration causes a gradual recession of a satellite in a prograde orbit away from the primary, and a corresponding slowdown of the primary's rotation.

The similar process of tidal deceleration occurs for satellites that have an orbital period that is shorter than the primary's rotational period, or that orbit in a retrograde direction.

The naming is somewhat confusing, because the speed of the satellite relative to the body it orbits is decreased as a result of tidal acceleration, and increased as a result of tidal deceleration.
Here is the problem: if the orbital motion of the earth around the moon is able to slow down the earth's rotation speed, then shouldn't the orbital motion of the earth-moon system around the sun be able to slow down the earth/moon's orbital speed, or on a larger scale, shouldn't the orbital motion of the solar system around the galaxy core be able to slow down the solar system's orbital speed?

Of course, there is a difference between orbital rotations and proper rotations of planets, but as it emerges from this actual discussion on tides (https://www.thenakedscientists.com/forum/index.php?topic=49715.new#new), the tidal bulges are not affected by that difference since they depend only on gravitational forces, so if it is true, I think that the two kinds of rotation should produce the same tidal effects. Unfortunately, the tidal theory says that the deceleration of the proper rotational speed of the earth is due to tidal friction opposing it, and that the deceleration of the orbital speed of the earth/moon system is due to the tidal bulges being dragged sideways by that friction. Since the proper rotation speed of the earth is working against the bulges, I can imagine how it would decelerate, but I can't imagine how the resultant offset of the bulges would decelerate the orbital speed of the earth/moon system. As they are presented on the wiki page (https://en.wikipedia.org/wiki/Tidal_acceleration#Effects_of_Moon's_gravity), those offset bulges would on the contrary accelerate the orbital speed of the moon, which is probably why it has been confusedly named "Tidal acceleration".

I looked for a more precise explanation of the mechanism but I didn't find any. Does anybody know how it works exactly?

 
Title: Re: Is Wiki right about tidal acceleration?
Post by: Halc on 22/09/2018 16:31:20
Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon), and the primary planet that it orbits (e.g. Earth). The acceleration causes a gradual recession of a satellite in a prograde orbit away from the primary, and a corresponding slowdown of the primary's rotation.
It requires one or both bodies to be spinning faster than the orbital angular velocity, so Earth transfers this kinetic energy to the moon, and it recedes.  The tides on the sun transfer the sun's rotational energy to the Earth, so it recedes from the sun.  The solar tides on Earth do drag the total angular momentum of the Earth/moon system down, so yes, eventually that effect will be greater and the moon will turn around and begin to approach Earth again and the days will begin to grown longer, with no lunar tides at all.
Of course before this happens, the earth will get swallowed by the sun as it expands, so don't mark it on your calendar.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Janus on 22/09/2018 17:01:00
. Since the proper rotation speed of the earth is working against the bulges, I can imagine how it would decelerate, but I can't imagine how the resultant offset of the bulges would decelerate the orbital speed of the earth/moon system. As they are presented on the wiki page (https://en.wikipedia.org/wiki/Tidal_acceleration#Effects_of_Moon's_gravity), those offset bulges would on the contrary accelerate the orbital speed of the moon, which is probably why it has been confusedly named "Tidal acceleration".

I looked for a more precise explanation of the mechanism but I didn't find any. Does anybody know how it works exactly?

 
The offset of the bulges produces a net forward pull or acceleration of the Moon in its orbit.  The key here is that the Moon is in orbit.  Giving something in orbit a forward push causes it to climb higher in its orbit, but in doing so, it trades off kinetic energy for gravitational potential energy. 
So let's say that you are trying to move a satellite from one orbit to a higher one.  This can be done by a two step process. 
First you give the satellite a forward boost. This changes its orbit into an elliptical one with its present orbit at perigee and the new orbit at apogee.  Wait for 1/2 orbit, and the satellite will be at apogee.  But in climbing away from the Earth, it loses speed. By the time it gets to apogee, it is moving slower than it needs to be to hold a circular orbit at that distance (even though this speed is less than the speed it had in the original orbit.).
so now you give it another forward boost to get it up to circular orbit speed.   Two forward boosts gets you to a higher orbit but moving at a lower speed.
With the Moon, it is under a small constant thrust.  It is an acceleration because this forward push always has it moving just a bit faster than it needs to for its altitude,  which causes it  to climb away.   And because of the trade off between climbing and speed, it loses orbital velocity in the process.( Though its velocity always remains a bit more than circular orbital velocity at any time.)  It's total orbital energy increases even though the kinetic energy portion decreases.

With the Interaction between Earth and Sun, it would be the tidal bulge created by the Earth on the Sun that would have an effect on the Orbit of the Earth around the Sun.  There are a number of factors that come into play here.  The Sun is a gaseous body, Which changes the drag between Sun and bulge, also the Sun doesn't rotate all in one piece.
There are also other planets orbiting the Sun creating their own bulges.  Jupiter, 5 times further away and with 333 times the mass, has 2 2/3 more tidal effect on the Sun than the Earth does.  Venus, Though slightly less massive is close enough to the Sun to have twice the tidal effect of the Earth. Since these tidal bulges will be following their respective planets, (sometimes complimenting each other and sometimes opposing) and not the Earth, you have a complicated scenario.
With the Galaxy you are dealing with a structure that is entirely composed of Orbiting objects.    There is no equivalent of the tidal friction you get with a planet.   And even if you had a central body to raise tides on, since the stars of the galaxy are even distributed around the center,  you wouldn't get a bulge  with unidirectional lobes ( like those pointing towards and away from the Moon)  All the stars would be trying to create a bulge in their direction and they would cancel each other out.  No lobes, no tidal acceleration.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 23/09/2018 14:08:11
So let's say that you are trying to move a satellite from one orbit to a higher one.  This can be done by a two step process.
First you give the satellite a forward boost. This changes its orbit into an elliptical one with its present orbit at perigee and the new orbit at apogee.  Wait for 1/2 orbit, and the satellite will be at apogee.  But in climbing away from the Earth, it loses speed. By the time it gets to apogee, it is moving slower than it needs to be to hold a circular orbit at that distance (even though this speed is less than the speed it had in the original orbit.).
so now you give it another forward boost to get it up to circular orbit speed. Two forward boosts gets you to a higher orbit but moving at a lower speed.
Hi Janus,

The theory says that when the first boost is forward, the second one must be backward because the satellite is then going too fast to execute a circular orbit at this new higher altitude, and that this second boost must also happen immediately if we want the orbit to immediately get circular.

With the Moon, it is under a small constant thrust. It is an acceleration because this forward push always has it moving just a bit faster than it needs to for its altitude,  which causes it to climb away.
That's what I thought too when I saw the offset bulges at Wiki.

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And because of the trade off between climbing and speed, it loses orbital velocity in the process.( Though its velocity always remains a bit more than circular orbital velocity at any time.)  It's total orbital energy increases even though the kinetic energy portion decreases.
Your trade off between kinetic energy and gravitational potential energy looks as if no backward boost was needed to slow down the speed. It is so if we want the trajectory to become elliptic, but adding constant tiny forward boosts to a satellite which just got at the perigee of an elliptic trajectory doesn't slow down its speed. To increase its altitude constantly while slowing its speed constantly, we need to accelerate it a bit and immediately decelerate it to its new orbit, and do it over and over constantly. That's what we would need to do with a satellite, and that's also what we would need to do if it was at the place of the moon.

To me, that tidal acceleration theory looks a bit circular: it means that the force exerted by the moon on the earth would finally profit to the moon. I wouldn't mind if it was clear, but I still don't get it. If I would simulate it for instance, it certainly wouldn't produce a recessing, and if a motion can't be simulated, it can't be calculated either, which is actually the case of the calculations on the wiki page: they are only about the constant forward torque produced by the offset bulges of the earth on the moon, nothing about any backward one.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 23/09/2018 16:39:52
The solar tides on Earth do drag the total angular momentum of the Earth/moon system down
Hi Halc,

What you say means that the boost from the moon's offset tides on the earth's orbital speed has to be equivalent to the boost from the earth's offset tides on the orbital speed of the moon. But is it really? In principle, the bulges get forwardly offset by the forward proper rotational speed of the planets, and the proper rotational speed of the moon is far from being the same as the earth's one, so its bulges get lot less offset while also getting a lot less massive. Of course, the earth needs to get less orbital speed than the moon for them to stay inline with their common barycenter because it is nearer to it, but it is a lot more massive than the moon too, so it is a lot more difficult to move around. If the moon's offset bulge was the same as the earth's one, the two boosts might be equivalent, but with less offset, I don't think they could. Besides, I explained to Janus how a backward boost was lacking in the "tidal acceleration" explanation, and it would still be lacking even if both accelerations were equivalent.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Halc on 23/09/2018 17:03:07
Quote from: Halc
The solar tides on Earth do drag the total angular momentum of the Earth/moon system down
Hi Halc,

What you say means that the boost from the moon's offset tides on the earth's orbital speed has to be equivalent to the boost from the earth's offset tides on the orbital speed of the moon.
The comment above refers to the solar tides on Earth, not tides caused by the moon.  That friction slows down the spin of Earth but has no immediate significant effect on the moon.

The lunar tides transfer momentum from Earth to the moon.  Total momentum must be conserved, but not total energy, which gets lost to heat of tidal friction.

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Besides, I explained to Janus how a backward boost was lacking in the "tidal acceleration" explanation, and it would still be lacking even if both accelerations were equivalent.
Your comment about backwards boost is mistaken.  Two forward boosts are required to move a satellite to a new higher orbit, as Janus correctly conveyed.  The moon on the other hand gets a small but continuous forward force which slowly adds to its mechanical energy, stealing away Earth’s mechanical energy.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Janus on 23/09/2018 19:03:08
So let's say that you are trying to move a satellite from one orbit to a higher one.  This can be done by a two step process.
First you give the satellite a forward boost. This changes its orbit into an elliptical one with its present orbit at perigee and the new orbit at apogee.  Wait for 1/2 orbit, and the satellite will be at apogee.  But in climbing away from the Earth, it loses speed. By the time it gets to apogee, it is moving slower than it needs to be to hold a circular orbit at that distance (even though this speed is less than the speed it had in the original orbit.).
so now you give it another forward boost to get it up to circular orbit speed. Two forward boosts gets you to a higher orbit but moving at a lower speed.
Hi Janus,

The theory says that when the first boost is forward, the second one must be backward because the satellite is then going too fast to execute a circular orbit at this new higher altitude, and that this second boost must also happen immediately if we want the orbit to immediately get circular.
No.   You always end up with less speed when you reach the higher orbit altitude then needed to hold a circular orbit there.    Orbital velocity at any point of an orbit is found by
 V = sqrt(u(2/r-1/a)
Where u is the gravitational parameter ( 3.987e14 m^3/s^2 for the Earth)
r is the present radial distance of the orbit
a is the semi-major axis

start with a circular orbit with r= 8,000,0000 m
you want to move to an circular orbit of r = 10,000,000 m
This makes a=9,000,000 m
Circular orbital velocity at original orbit = sqrt(u/r) = 7059.6 m/s
Perigee velocity of orbit with perigee at 8,000,000 m(r=8,000,000m) and apogee at 10,000,000m = 7441.4 m/s
Meaning a delta V requirement of + 381.8 m/s to leave the original orbit and enter the transfer orbit.
Apogee velocity of transfer orbit (r=10,000,000) = 5953.2 m/sec
Circular orbital velocity at 10,000,000m = 6314.3 m/sec
Meaning a delta V requirement of +361.6m/sec to achieve that circular orbit.
a total forward delta V of 742.9 m/s  but a net loss of 745.3 m/s in terms of orbital velocity.
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With the Moon, it is under a small constant thrust. It is an acceleration because this forward push always has it moving just a bit faster than it needs to for its altitude,  which causes it to climb away.
That's what I thought too when I saw the offset bulges at Wiki.

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And because of the trade off between climbing and speed, it loses orbital velocity in the process.( Though its velocity always remains a bit more than circular orbital velocity at any time.)  It's total orbital energy increases even though the kinetic energy portion decreases.
Your trade off between kinetic energy and gravitational potential energy looks as if no backward boost was needed to slow down the speed. It is so if we want the trajectory to become elliptic, but adding constant tiny forward boosts to a satellite which just got at the perigee of an elliptic trajectory doesn't slow down its speed.
Increasing velocity at perigee increases the apogee. Increasing speed at apogee increases perigee.  If you are at apogee and want to circularize your orbit, you want to raise the perigee up to your present altitude. This requires an increase in velocity.
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To increase its altitude constantly while slowing its speed constantly, we need to accelerate it a bit and immediately decelerate it to its new orbit, and do it over and over constantly. That's what we would need to do with a satellite, and that's also what we would need to do if it was at the place of the moon.
Once again, NO. 
Total orbital energy is Kinetic energy plus Gravitational potential energy or mv^2/2-um/r  where m is the mass of the satellite.
Assuming a unit mass for m, we can use v^2/2-u/r
It can also be given as -u/2a  where a is again the semi-major axis. (for a circular orbit a=r)
Starting in a circular orbit, increasing v increases the KE while GPE remains constant, it also raises a.  Total E has increased. But as the mass starts to climb from its original altitude its total energy remains the same, but its GPE increases. This means it must lose KE and thus velocity.
Again going back to our 8,000,000m to 10,000,000m change in altitude.
We start with a total  specific(per kg) energy of  7059.6^2/2 - 3.987e14/8,000,000 = -24918524 j/kg
We boost the speed to 7441.4 m/s pumping up the energy to -22150283 j/kg ( less negative means an increase)
This total remains constant as the mass climbs to it apogee of 10,000,000 m so
-22150283 =  v^2/2- 3.987e14/10,000,000
v^2 = 2(3.987e14/10,000,000 - 22150283) = 35439434
v= 5953.1 m/s ( within 0.1 m/sec of the answer I got above  and well within the rounding error margin.)
Your conclusion that you would need to brake upon reaching apogee is completely the opposite of what the actual physics says.
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To me, that tidal acceleration theory looks a bit circular: it means that the force exerted by the moon on the earth would finally profit to the moon. I wouldn't mind if it was clear, but I still don't get it. If I would simulate it for instance, it certainly wouldn't produce a recessing, and if a motion can't be simulated, it can't be calculated either, which is actually the case of the calculations on the wiki page: they are only about the constant forward torque produced by the offset bulges of the earth on the moon, nothing about any backward one.

The only backward one is the drag the bulges produce on the rotation of the Earth slowing its rotation rate.  There doesn't need to be a backward force on the Moon.  Its orbital velocity decreases due to its climbing away from the Earth even though there is a constant "forward" pull.    As counter-intuitive as this seems, this is how orbital mechanics works.
"Forward takes you out, out takes you back, back takes you in, and in takes you forward"
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 23/09/2018 21:34:36
OK. I just realized that you were both talking about the Hohmann transfer orbit, whereas I was taking about an immediate one. To get a Hohmann transfer, we have to wait till the satellite gets to its apogee, and then accelerate it again to get a circular orbit, whereas if we don't want to wait, then we can decelerate it immediately after having accelerated it. If I understand well, you mean that the moon suffers a tiny boost, waits till it gets at its apogee, and then uses another boost to stay on a circular orbit. That would be fine if no other boost would be happening in between and if the moon knew what it was doing, but it is not the case. The boosts happen all along the trajectory, so how does the moon differentiate the first boosts from the second ones. Moreover, if I had to simulate that motion, I might probably get the same kind of slow spiraling trajectory, but I can't figure out how the speed would ever get down.
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Quote from: Le Repteux
To me, that tidal acceleration theory looks a bit circular: it means that the force exerted by the moon on the earth would finally profit to the moon. I wouldn't mind if it was clear, but I still don't get it. If I would simulate it for instance, it certainly wouldn't produce a recessing, and if a motion can't be simulated, it can't be calculated either, which is actually the case of the calculations on the wiki page: they are only about the constant forward torque produced by the offset bulges of the earth on the moon, nothing about any backward one.
The only backward one is the drag the bulges produce on the rotation of the Earth slowing its rotation rate.  There doesn't need to be a backward force on the Moon.  Its orbital velocity decreases due to its climbing away from the Earth even though there is a constant "forward" pull. As counter-intuitive as this seems, this is how orbital mechanics works.
As I just said, we can also decelerate a satellite immediately after having accelerated it, and it will also follow a circular trajectory. It takes more energy than waiting till it decelerates all by itself, but it works. This way, if we accelerate it continuously as it is the case with the tidal explanation, it will simply never slow down. That's what we do when we want a satellite to escape the earth's gravitational acceleration. To me, accelerating it as little as the tides would do (and also accelerating it less and less), would only take it more time to reach the same height: it would not slow it down. I have another explanation that looks promising, but I'll wait till I'm convinced that I can't understand the tidal one before talking about it, so thanks for digging it out further.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Halc on 23/09/2018 22:15:22
If I understand well, you mean that the moon suffers a tiny boost, waits till it gets at its apogee, and then uses another boost to stay on a circular orbit.
 That would be fine if no other boost would be happening in between and if the moon knew what it was doing, but it is not the case. The boosts happen all along the trajectory, so how does the moon differentiate the first boosts from the second ones.
The force on the moon is continuous, and so the orbit is technically a continuous spiral, never a circle.  The satellites could get to a higher orbit the same way, but rockets are typically not designed to run at low power like that, and the people that paid for it want it there more quickly I suppose.

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if we accelerate it continuously as it is the case with the tidal explanation, it will simply never slow down.
The speed of the moon is continuously slowing down due to gradually going into a higher orbit, as is pointed out in the last line of the wiki article you quote in the OP.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Janus on 24/09/2018 01:42:29
OK. I just realized that you were both talking about the Hohmann transfer orbit, whereas I was taking about an immediate one. To get a Hohmann transfer, we have to wait till the satellite gets to its apogee, and then accelerate it again to get a circular orbit, whereas if we don't want to wait, then we can decelerate it immediately after having accelerated it. If I understand well, you mean that the moon suffers a tiny boost, waits till it gets at its apogee, and then uses another boost to stay on a circular orbit. That would be fine if no other boost would be happening in between and if the moon knew what it was doing, but it is not the case. The boosts happen all along the trajectory, so how does the moon differentiate the first boosts from the second ones. Moreover, if I had to simulate that motion, I might probably get the same kind of slow spiraling trajectory, but I can't figure out how the speed would ever get down.
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Quote from: Le Repteux
To me, that tidal acceleration theory looks a bit circular: it means that the force exerted by the moon on the earth would finally profit to the moon. I wouldn't mind if it was clear, but I still don't get it. If I would simulate it for instance, it certainly wouldn't produce a recessing, and if a motion can't be simulated, it can't be calculated either, which is actually the case of the calculations on the wiki page: they are only about the constant forward torque produced by the offset bulges of the earth on the moon, nothing about any backward one.
The only backward one is the drag the bulges produce on the rotation of the Earth slowing its rotation rate.  There doesn't need to be a backward force on the Moon.  Its orbital velocity decreases due to its climbing away from the Earth even though there is a constant "forward" pull. As counter-intuitive as this seems, this is how orbital mechanics works.
As I just said, we can also decelerate a satellite immediately after having accelerated it, and it will also follow a circular trajectory. It takes more energy than waiting till it decelerates all by itself, but it works. This way, if we accelerate it continuously as it is the case with the tidal explanation, it will simply never slow down. That's what we do when we want a satellite to escape the earth's gravitational acceleration. To me, accelerating it as little as the tides would do (and also accelerating it less and less), would only take it more time to reach the same height: it would not slow it down. I have another explanation that looks promising, but I'll wait till I'm convinced that I can't understand the tidal one before talking about it, so thanks for digging it out further.

If the forward force is high enough, then, under a constant force, the satellite can both gain altitude and velocity.  However, below a certain threshold, the velocity lost climbing exceeds the velocity that would have been gained through the application of the forward thrust over the same period.  This is the situation that the Moon finds itself in.  The forward force is below this threshold and it loses orbital velocity as it spirals away from the Earth even though it is under a constant forward force,
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 24/09/2018 15:22:36
If the forward force is high enough, then, under a constant force, the satellite can both gain altitude and velocity. However, below a certain threshold, the velocity lost climbing exceeds the velocity that would have been gained through the application of the forward thrust over the same period. This is the situation that the Moon finds itself in. The forward force is below this threshold and it loses orbital velocity as it spirals away from the Earth even though it is under a constant forward force,
Interesting possibility, so let's analyze it. The boost from the tides is constant even if it is getting weaker and weaker with time since the altitude increases constantly and since the tides themselves get lower. A small portion of the boost does the same thing, and a portion of that portion too. The smallest portions we can analyze all do the same thing: they succeed to bring the moon at a higher altitude while increasing its orbital speed. There is no break between those boosts that could let the speed get down. If there was any, the moon would effectively slow down and get away from the earth a bit, but there is none. Each small boost is immediately followed by another one, so to me, those boosts can do nothing else than to constantly increase the speed even if their force is constantly getting down. If you got a link to the threshold explanation, can I have it so that I can study it more thoroughly please?
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 24/09/2018 15:35:57
The speed of the moon is continuously slowing down due to gradually going into a higher orbit, as is pointed out in the last line of the wiki article you quote in the OP.
I'm looking for a mechanism that I could simulate, and I'm afraid there is no way to simulate that kind of deceleration but to add an ad hoc equation to the coding that fits the data.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 25/09/2018 18:17:28
This thread on tides emerged from another one that I had decided to leave because it wasn't progressing, but unexpectedly, it did. Colin2B decided to answer an unanswered proposition that I had posted about the tidal phenomenon, and he agrees with it, so I refer you to it (https://www.thenakedscientists.com/forum/index.php?topic=49715.msg554997#msg554997) since it is precisely the one I was about to make here. Feel free to discuss it here though since this thread's subject is more specific than the other one.
Title: Re: Is Wiki right about tidal acceleration?
Post by: rmolnav on 27/09/2018 11:23:11
The boost from the tides is constant even if it is getting weaker and weaker with time since the altitude increases constantly and since the tides themselves get lower. A small portion of the boost does the same thing, and a portion of that portion too. The smallest portions we can analyze all do the same thing: they succeed to bring the moon at a higher altitude while increasing its orbital speed. There is no break between those boosts that could let the speed get down. If there was any, the moon would effectively slow down and get away from the earth a bit, but there is none.
Please kindly note that what in bold is what is actually happening !!
Orbiting dynamics is not my forte, but I think that, apart from transient changes in the direction of earth´s pull on the moon (along each quarter cycle between apogee and perigee), with each cycle moon changes some kinetic energy into potential energy (as Janus says), it gets a little farther, and orbits with a little lower tangential speed ... , despite the fact that initially increases in tangential speed (caused by the gap between actual moon´s and "sublunar" bulge´s locations) do happen, but the bottom line is a tangential speed decrease.
 
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 27/09/2018 14:19:23
but the bottom line is a tangential speed decrease.
It is, and it supposedly depends on the bulges being dragged forward by rubbing against the earth's daily rotation, what offsets them a bit, and what in return accelerates the moon forward on its orbital trajectory. It would work if the moon wouldn't have to slow down while getting to a higher orbit, but it has, and the only mechanism we have to explain that is math: the moon supposedly slows down because it transforms its kinetic energy into potential energy. That would be true if we would let it go after having accelerated it a bit, it would then slow down all by itself until it would have reached its apogee, but the forward pull by the offset bulge never stops, so I can't see where the speed would have the time to get down.
Title: Re: Is Wiki right about tidal acceleration?
Post by: rmolnav on 27/09/2018 18:38:55
... but the forward pull by the offset bulge never stops, so I can't see where the speed would have the time to get down.
The forward force is below this threshold and it loses orbital velocity as it spirals away from the Earth even though it is under a constant forward force,
You both are forgetting a small, but possibly important, detail.
Perhaps what I said on my post is not just to say "apart from ...":
...apart from transient changes in the direction of earth´s pull on the moon (along each quarter cycle between apogee and perigee)
I meant that sublunar bulge pull tangential component is actually not constant, due to the fact that only where apogee (and almost where perigee) the full pull vector is perpendicular to moon´s path ...
Perhaps the "effective" tangential bulge pull decreases from perigee to apogee more than what increases from apogee to perigee ...
Janus, your knowledge on this field is much deeper than ours (at least than mine ...). Any comment from you would be really appreciated. 

Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 27/09/2018 19:28:47
I meant that sublunar bulge pull's tangential component is actually not constant, due to the fact that only where apogee (and almost where perigee) the full pull vector is perpendicular to moon´s path ...
Perhaps the "effective" tangential bulge pull decreases from perigee to apogee more than what increases from apogee to perigee ...
Even when the trajectory is not circular, the pulling component cannot be anything else that perpendicular, and the inertial one tangential, so even if the strength of the radial force changes all along the trajectory, it is still there, and it doesn't stop accelerating the tangential speed forward.
Title: Re: Is Wiki right about tidal acceleration?
Post by: rmolnav on 28/09/2018 11:43:20
Even when the trajectory is not circular, the pulling component cannot be anything else that perpendicular, and the inertial one tangential
I can´t agree with that ...
Earth, located on one of the focus of an ellipse (moon´s trajectory), pulls the moon through a force vector with main component certainly perpendicular to moon´s trajectory, but also through other tangential one not null on most moon´s locations ...
The perpendicular component is the one which actually exerts as centripetal force, and points not towards the ellipse´s focus, but towards the center of curvature of the orbit at the considered point.
And the tangential component (by the way, I wouldn´t call it "the inertial one") tends to increase moon´s tangential speed along parts of the orbit, and decrease along the rest
SIMILAR THINGS can be said about the additional bulge pull we are discussing ... Its tangential component varies with the varying angle between the bulge´s center-moon´s CM and the elliptical trajectory ...
I won´t even guess whether at some parts of the orbit that bulge tangential pull can be "negative", but it´s quite clear it increases along parts of the orbit, and decreases along the rest.
And, as far as I can understand, that can affect the bottom line: after each complete cycle (28/29 days), moon is farther (though only a very tiny little bit), and its tangential speed is very, very little smaller !!
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 29/09/2018 20:34:39
Earth, located on one of the focus of an ellipse (moon´s trajectory), pulls the moon through a force vector with main component certainly perpendicular to moon´s trajectory, but also through other tangential one not null on most moon´s locations ...
You're right about the force not always being perpendicular to the tangential motion if the trajectory is an ellipse, but I still can't figure out how that tangential motion could slow down while constantly being accelerated. At least, with the idea that it is the orbital speed that raises the tides, the motion becomes an acceleration followed by a deceleration, and such a tangential action is precisely what is needed to change the height of a circular trajectory without waiting for the satellite to get to its apogee. This way, each point of the surface would be accelerated to a higher orbit during its transit, and then decelerated back to almost where its was at the beginning of the transit. Remains to determine why the "almost".

Let's try another explanation. One of the phenomenon we don't usually account for when studying orbital motion is aberration. We don't think of it because we don't study gravitation in terms of information traveling in void, thus in terms of light. We know that the motion of the earth produces aberration on the light from the stars, so it certainly produces some on the information from the moon. That information should pull the earth forward a bit since it is offset and it should also pull it stronger since it is blueshifted, but it is also sent backward a bit by the moon in order to hit the moving earth in time, which produces redshift, while the offset it produces is completely rectified by the one from aberration later on, so the blueshift subtracts from the redshift but not completely since the moon is going faster and produces more redshift than the blueshift the earth produces, thus when the earth uses that information, it is still redshifted a bit and so doesn't produce as much acceleration as it should to keep the earth at a constant distance from the moon. During that time, the inverse is happening to the moon: the information is sent backwards by the earth and the moon produces aberration on it, so it also appears to come at right angle but this time, the redshift produced by the earth is less important than the blueshift produced by the moon, and it should thus produce more acceleration than is needed to keep the moon at a constant distance from the earth. So it doesn't seem to work, but fortunately, since aberration is a relativistic effect, we can count on the increase in mass due to motion to justify the surplus of force applied on the moon, and to the less important increase in mass of the earth to justify the lack of force applied on the earth. This way, the orbital motion appears to be saved, but the recessing one is not.

Let's try another one then. What if the slow recessing of the earth/moon system was due to a constant slow shortening of the atoms' wavelengths? This way, the time a laser pulse takes to make a roundtrip might only appear to take longer, because it would simply be due to our clocks getting faster with time while c would stay constant. That phenomenon would produce redshift, which might explain some of the gravitational anomalies that we observe, from the probes getting slower to the galaxies fleeing away, but it would also explain gravitation itself, because all the bodies that are actually orbiting would have to use an information that looks redshifted to stay at the right orbital distance, so they would all need to accelerate towards one another to blueshift it a bit. The farther they would be from one another, the larger would be the shift but the weaker would be the force, because the shift would only increase with distance whereas we know that the intensity of the information diminishes with the square of the distance. That's my favorite explanation, but I admit it is a bit hard to swallow.
Title: Re: Is Wiki right about tidal acceleration?
Post by: rmolnav on 01/10/2018 12:35:08
Quote from: rmolnav on 28/09/2018 11:43:20
Earth, located on one of the focus of an ellipse (moon´s trajectory), pulls the moon through a force vector with main component certainly perpendicular to moon´s trajectory, but also through other tangential one not null on most moon´s locations ...
You're right about the force not always being perpendicular to the tangential motion if the trajectory is an ellipse, but I still can't figure out how that tangential motion could slow down while constantly being accelerated .
What in bold is not always so, I guess ... The "misalignment" of sublunar bulge´s pull is very, very tiny (moon is some sixty times earth radius away ...), and that could be insufficient to give a "positive" tangential pull where the lack of perpendicularity with the elliptical orbit is "negative" ...
AND REGARDING:
Let's try another explanation. One of the phenomenon we don't usually account for when studying orbital motion is aberration. We don't think of it because we don't study gravitation in terms of information traveling in void, thus in terms of light. We know that the motion of the earth produces aberration on the light from the stars, so it certainly produces some on the information from the moon. That information should pull the earth forward a bit since it is offset and it should also pull it stronger since it is blueshifted, but it is also sent backward a bit by the moon in order to hit the moving earth in time, which produces redshift, while the offset it produces is completely rectified by the one from aberration later on, so the blueshift subtracts from the redshift but not completely since the moon is going faster and produces more redshift than the blueshift the earth produces, thus when the earth uses that information, it is still redshifted a bit and so doesn't produce as much acceleration as it should to keep the earth at a constant distance from the moon. During that time, the inverse is happening to the moon: the information is sent backwards by the earth and the moon produces aberration on it, so it also appears to come at right angle but this time, the redshift produced by the earth is less important than the blueshift produced by the moon, and it should thus produce more acceleration than is needed to keep the moon at a constant distance from the earth. So it doesn't seem to work, but fortunately, since aberration is a relativistic effect, we can count on the increase in mass due to motion to justify the surplus of force applied on the moon, and to the less important increase in mass of the earth to justify the lack of force applied on the earth. This way, the orbital motion appears to be saved, but the recessing one is not.

Let's try another one then. What if the slow recessing of the earth/moon system was due to a constant slow shortening of the atoms' wavelengths? This way, the time a laser pulse takes to make a roundtrip might only appear to take longer, because it would simply be due to our clocks getting faster with time while c would stay constant. That phenomenon would produce redshift, which might explain some of the gravitational anomalies that we observe, from the probes getting slower to the galaxies fleeing away, but it would also explain gravitation itself, because all the bodies that are actually orbiting would have to use an information that looks redshifted to stay at the right orbital distance, so they would all need to accelerate towards one another to blueshift it a bit. The farther they would be from one another, the larger would be the shift but the weaker would be the force, because the shift would only increase with distance whereas we know that the intensity of the information diminishes with the square of the distance. That's my favorite explanation, but I admit it is a bit hard to swallow.
YOU ARE RIGHT on what in bold ...
And all those things relative to forces on earth and/or moon caused by "optical" phenomena caused their speeds are, to me, utterly absurd !!
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 01/10/2018 22:29:51
And all those things relative to forces on earth and/or moon caused by "optical" phenomena caused their speeds are, to me, utterly absurd !!
Optical phenomenon are measured with instruments made out of atoms, and since those atoms move according to the direction and the intensity of the gravitational force applied on them, then we can deduce that the direction and the speed they take while being accelerated depend on any optical phenomenon they suffer during that moment. When we observe a star, we have to tilt our telescope a bit in the direction the earth is moving to account for the aberration phenomenon, so it means that the atoms of the earth are actually accelerating in this direction with regard to the star because the pulling from the star is also bent by the aberration phenomenon. It wouldn't be the case if gravitation was instantaneous, but it's not.

What in bold is not always so, I guess ... The "misalignment" of sublunar bulge´s pull is very, very tiny (moon is some sixty times earth radius away ...), and that could be insufficient to give a "positive" tangential pull where the lack of perpendicularity with the elliptical orbit is "negative" ...
When the direction of the force is not perpendicular to the trajectory of a body, the tangential component affects its tangential speed, and the perpendicular one affects its direction. In the case of an orbital trajectory, these two components produce an elliptical trajectory whenever they are not perpendicular to one another. Adding a small offset force should affect the elliptical trajectory of a body the same way it produces it: where the body is moving away from the force, it should slow down its tangential speed a bit faster than it is actually slowing and curve its direction a bit faster than it is actually curved, and where it is moving closer, it should increase its tangential speed a bit faster than it is actually increasing and curve its direction a bit faster than it is actually increasing too. It's hard to tell what the resulting trajectory would be, but it helped me to realize that I did not account for the perpendicular component in my analysis of the tidal acceleration when the orbit is circular. In this case, while the tangential component would be accelerating the tangential speed, the perpendicular one would be pulling the moon stronger since it is closer to it. This way, the bulges would only produce a lower orbit, and the increased speed would be normal, but once in a lower orbit, the bulges would increase, and so would the speed and the force, which means that the orbital distance would contract instead of expanding, which is not what we observe.

Know what? I think it is clearer to consider that the cg of the earth is not affected by the bulges, and safer to discard the tidal acceleration hypothesis. Here is wiki's unclear explanation using the conservation of energy principle, which is not a mechanism anyway: (https://en.wikipedia.org/wiki/Tidal_acceleration#Angular_momentum_and_energy)
Quote
The gravitational torque between the Moon and the tidal bulge of Earth causes the Moon to be constantly promoted to a slightly higher orbit and Earth to be decelerated in its rotation. As in any physical process within an isolated system, total energy and angular momentum are conserved. Effectively, energy and angular momentum are transferred from the rotation of Earth to the orbital motion of the Moon (however, most of the energy lost by Earth (−3.321 TW)[citation needed] is converted to heat by frictional losses in the oceans and their interaction with the solid Earth, and only about 1/30th (+0.121 TW) is transferred to the Moon). The Moon moves farther away from Earth (+38.247±0.004 mm/y), so its potential energy (in Earth's gravity well) increases. It stays in orbit, and from Kepler's 3rd law it follows that its angular velocity actually decreases, so the tidal action on the Moon actually causes an angular deceleration, i.e. a negative acceleration (−25.858±0.003"/century2) of its rotation around Earth. The actual speed of the Moon also decreases. Although its kinetic energy decreases, its potential energy increases by a larger amount.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Halc on 01/10/2018 22:44:25
Quote from: wiki
As in any physical process within an isolated system, total energy and angular momentum are conserved.
Angular momentum is conserved yes, but a pure Earth/moon system is hardly a closed system.  Total energy is always lost to friction.  I'm surprised to find that wording on a wiki page.  Yes, angular momentum of Earth is transferred to the moon, and the effect is very measurable.  Discard the tidal acceleration hypothesis if you want, but then you need to explain the moon moving away a very measurable 4 cm each year.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Halc on 01/10/2018 22:52:40
OK, the wiki does admit that only a 30th of the energy is transferred to the moon, and the rest is lost to friction.
The initial comment sort of said otherwise, but I guess 'isolated' system doesn't mean a closed one.
Title: Re: Is Wiki right about tidal acceleration?
Post by: rmolnav on 02/10/2018 11:46:54
Adding a small offset force should affect the elliptical trajectory of a body the same way it produces it: where the body is moving away from the force, it should slow down its tangential speed a bit faster than it is actually slowing and curve its direction a bit faster than it is actually curved, and where it is moving closer, it should increase its tangential speed a bit faster than it is actually increasing and curve its direction a bit faster than it is actually increasing too.
But no force is actually added because of tides ... Total earth´s pull keeps constant, but very slightly changes "inclination" relative to the orbit.
Therefore, tangential component increases and decreases, with their corresponding decreases and increases of perpendicular component, the one which actually counts for curvature ...
And regarding:
Optical phenomenon are measured with instruments made out of atoms, and since those atoms move according to the direction and the intensity of the gravitational force applied on them, then we can deduce that the direction and the speed they take while being accelerated depend on any optical phenomenon they suffer during that moment.
I have to say that optics is not my forte ... But I consider thinking those interactions between optical phenomena, speeds taken by used instrument atoms (or other earth atoms), and gravitational forces applied on them, might have a not completely insignificant influence on orbits, tides, etc. is utterly absurd !!
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 02/10/2018 16:22:23
I have to say that optics is not my forte ... But I consider thinking those interactions between optical phenomena, speeds taken by used instrument atoms (or other earth atoms), and gravitational forces applied on them, might have a not completely insignificant influence on orbits, tides, etc. is utterly absurd !!
Take a look at this simulation (http://motionsimulations.com/Acceleration%20with%20four%20particles) I made of four bonded particles. What bonds them is a standing wave made of light. A photon is sent vertically and another one horizontally between them while they are accelerating to the right. When the photons hit the particles, they automatically send back another one. The left particles accelerate before the right ones because the acceleration comes from the left. The idea is to move the particles so that the two photons keep on hitting the left upper particle at the same time. This way, the particles stay on the nodes of their standing wave, which is precisely what any particle bonding is made of. While hitting the start button, look at the way the particles behave when a photon strikes them. When the photons leave the particles, they contain the kinetic energy the particles carry in the form of doppler effect, and they transfer this energy to the other particles later on, which then accelerate and print on the photons they are sending back their own kinetic energy. Since the left particles accelerate before the right ones, the system contracts horizontally, and for the vertical photon to stay on sync with the horizontal one, it must also contract vertically, so whenever the vertical photon is late a bit, the vertical distance automatically contracts a bit, and it does so until the system is back on sync.

Once the simulation is on, you will notice that the vertical particle leaves a trace of its previous location on the screen. The more the speed increases, the more this trace is at angle to the vertical. This trace indicates the direction the photon has to take to hit the other particle, so it is also in this direction that it goes at the speed of light. In the Relativity theory, that phenomenon is called "beaming", and it is accompanied by another one called "aberration", where the direction of a photon is affected by the transverse speed that an observer has with regard to it. In our case, it happens when the vertical photon strikes a particle. If it would strike it vertically, aberration would indicate that it came from the right a bit, but it strikes at an angle due to beaming, so aberration simply indicates that it came at right angle, as if the system was not moving, which is why the particles move vertically when the two photons are getting out of sync a bit. In this case, the light that keeps the vertical particles bonded seems to come from the actual position of the other particles, but it is not the case for the light from the stars because we are not going at the same speed and in the same direction they are going. Because of aberration, when we look at a star, we do not see it where it actually is, and since gravitation travels at the speed of light, we can consider that its direction is also affected by the speed of the celestial bodies. If aberration of light due to the different rotational motions of the earth was so negligible, we would not be able to observe it, and we are. On the other hand, the offset the bulges take while being dragged by friction is so tiny that it is unobservable, it's only theoretical, and it depends on an energy calculation, and so does the transfer of energy from the earth's tides to the moon's slow recessing.

That said, I still think that aberration is useful to orbital motion, but not to recessing, for which I prefer my slow shortening of the particles' wavelengths. In my simulation with four bonded particles, the distance between them is contracting when they are accelerated, and constant acceleration is precisely what gravitation is about. While the distances contract, the time the photons take to make a roundtrip is contracting too, which means that the wavelength of their standing wave is also contracting, thus shortening, exactly as what I am suggesting. I'm probably still far from the truth, but that kind of simulation is nevertheless helpful to our understanding of what may be happening if interactions are not instantaneous at any scale. You won't find them on the scientific forums that forbid us to criticize Relativity though, because to move a photon on a screen the way I do, we have to accept that it is not always traveling at a constant speed with regard to the particles, thus that motion is not as relative as we thought it was. In fact, we have to believe that light travels in ether, and that the screen is at rest relative to it, which makes it an absolute reference frame, thus contradicting the relativity idea that all the reference frames are relative. But simulations do explain Relativity very well. Take a look at the one illustrating the Twins paradox, (http://motionsimulations.com/Twins%20paradox) and you will see that with the same screen at rest in ether, the two clocks do not display the same elapsed time once they are brought back together at the end.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 02/10/2018 18:33:53
Discard the tidal acceleration hypothesis if you want, but then you need to explain the moon moving away a very measurable 4 cm each year.
My orbital speed hypothesis and my aberration hypothesis do not seem to work, but my slow shortening of the particles' wavelengths seems to work. If our atomic clocks are constantly speeding up with time while the speed of light stays constant, the time light takes to make a roundtrip to the moon would seem to lengthen, and we could easily attribute it wrongly to an increase in distance if we also consider that the speed of light is constant because we depend on light to measure that kind of distance. As I said, that phenomenon would produce redshift, so it could also explain the cosmological redshift, but I also think that it could produce gravitation itself since it would give the particles the false information that they are moving away from one another with time, so they would be forced to accelerate constantly towards one another for the strength of their bonds to stay constant, and whatever the kind of bonding. It is an extremely circular phenomenon, but it doesn't mean that it doesn't work. I made a simulation with two bonded particles (http://motionsimulations.com/Acceleration%20with%20two%20particles) exchanging light and trying to keep the strength of their bond constant while being accelerated, and I got the same circularity, but it works. In that case, doppler effect is not only an effect from motion, but it also causes it. When we stop the acceleration, the blueshift produced on the photon by the motion to the right of the left particle produces the motion to the right of the right particle later on, which produces redshift on the photon it emits backwards to the left particle, which produces the motion to the right of the left particle later on. It is circular, but it works: this way, the strength of the bond stays constant whatever the speed of the system and even if the information exchanged is not instantaneous.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Halc on 02/10/2018 19:03:12
My orbital speed hypothesis and my aberration hypothesis do not seem to work, but my slow shortening of the particles' wavelengths seems to work. If our atomic clocks are constantly speeding up with time while the speed of light stays constant, the time light takes to make a roundtrip to the moon would seem to lengthen, and we could easily attribute it wrongly to an increase in distance if we also consider that the speed of light is constant because we depend on light to measure that kind of distance.
If that were true, everything else (other planets, the sun ...) would all similarly be receding from us.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 02/10/2018 20:30:25
If that were true, everything else (other planets, the sun ...) would all similarly be receding from us.
They would seem to be receding, which is precisely what the tidal acceleration hypothesis implies too in the case of the solar system. The phenomenon is difficult to observe though. We don't have mirrors on the sun to tell us if the distance seems to be increasing. Another observation has to be explained too: the geological Rhythmites (https://en.wikipedia.org/wiki/Rhythmite). Those layers show that there was more days in a month and more months in a year than there is now, but they don't tell us if there was also more years in one cycle around the galaxy, and if it was so, it could mean that all those cycles seem to slow down with time, whereas in reality, they would all stay proportional to the period of the involved cycles. Since gravitation is not instantaneous, that phenomenon would not be instantaneous either, and it would thus be affected by distance, so it could also explain why the galaxies seem to be receding from us at an accelerated rate.
Title: Re: Is Wiki right about tidal acceleration?
Post by: Halc on 02/10/2018 22:20:19
They would seem to be receding, which is precisely what the tidal acceleration hypothesis implies too in the case of the solar system.
For that matter, the building across the street would seem to be receding.  That's a pretty easy falsification test your hypothesis.
Title: Re: Is Wiki right about tidal acceleration?
Post by: rmolnav on 03/10/2018 19:02:45
My orbital speed hypothesis and my aberration hypothesis do not seem to work, but my slow shortening of the particles' wavelengths seems to work. If our atomic clocks are constantly speeding up with time while the speed of light stays constant, the time light takes to make a roundtrip to the moon would seem to lengthen, and we could easily attribute it wrongly to an increase in distance if we also consider that the speed of light is constant because we depend on light to measure that kind of distance. As I said, that phenomenon would produce redshift, so it could also explain the cosmological redshift, but I also think that it could produce gravitation itself since it would give the particles the false information that they are moving away from one another with time, so they would be forced to accelerate constantly towards one another for the strength of their bonds to stay constant, and whatever the kind of bonding. It is an extremely circular phenomenon, but it doesn't mean that it doesn't work
Again: to me all that sounds like an utterly absurd idea ...
Most eminent scientists, the ones from NASA among them, have for decades been measuring enormeous distances, with all sort of advanced instruments using electromagnetic radiations (infrared included), and they master radiations and all those frequency shifts you talk about ...
Also with sound, and recently with gravitational waves ...
And they give unbelievably precise figures ...
Do you honestly think none of them has even imagined what you refer to could be making all their measurements actually erroneous ??
If so, you should contact some of them and expose your ideas ...
If you google "NASA" and then enter "astronomy distance measurements" on the "questions" window, you´ll get a long list of articles on the subject ... On many of them you´ll find email direction of the author. Choose one and send him an e-mail.
I´ve done that several times (mainly discussing tides and centrifugal force), and they usually reply received e-mails ...
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 03/10/2018 22:53:11
Again: to me all that sounds like an utterly absurd idea ...
You are probably right about that, so at last, we found a common ground! :0)
Title: Re: Is Wiki right about tidal acceleration?
Post by: Le Repteux on 04/10/2018 16:57:11
They would seem to be receding, which is precisely what the tidal acceleration hypothesis implies too in the case of the solar system.
For that matter, the building across the street would seem to be receding. That's a pretty easy falsification test for your hypothesis.
We don't feel it because it is too weak, but buildings do exert a gravitational force on us, and whenever there is a force between two bodies, information is involved even if we can't detect it. Curved space is not an information, so it doesn't help us to understand what gravitation is really about. To discover it, I think we have to think in terms of light, and ask ourselves how it could inform bodies on their speed or their direction with regard to other bodies. Light has an absolute speed and absolute direction, and since particles are exchanging some, they can certainly use it to determine whether they are moving or not with regard to other particles, and they can certainly use it to know the direction they have with regard to them also. Doppler effect and aberration are not only human discoveries, they also really affect the energy and the direction of the light the particles emit and absorb, so they could really be a cause for the direction and the speed they take with regard to other particles.