Science Question, I'm stuck on

[vargo]

If the earth was billions of years old, the moon would be much farther away from the earth than it is, and its gently slowing rotation would have reached zero, The moon is still too close to the earth, and it still rotates at Approx. 1000 miles per hour, indictating that it is not billlions of years old??

[Ariphaos]

Not quite.

Remember, the moon's mass is only about 1% of that of Earth's, and gravitational tide locking isn't particularly quick. Last I checked, the Sun will scorch the Earth in its expansion and collapse into a white dwarf before the Moon has slowed Earth's rotation to once per ~30 days.

After which the Earth will drag the moon to it, break it apart and form a nice ring system.

Regardless, you may check
http://www.talkorigins.org/faqs/moonrec.html
For more information.

[Sriad]

It sounds like you're holding some misconceptions, or else are suffering from bad syntax. Anyway, here're your answers as far as I understood your questions:

"If the earth was billions of years old, the moon would be much farther away from the earth than it is, and its gently slowing rotation would have reached zero[...]"

The moon's "face" is now locked to the Earth and has been for some time. Gravitational systems defy normal intuitive understanding of entropy: as they decay the objects in the system speed up and appear to gain energy, but really they are losing the potential energy of seperation. As time goes on, the moon will get closer to Earth, not farther away.

The Earth's rotation is slowing down too; Dinosaur days were around 23 hours long, and highly accurate scientific time pieces insert leap-milliseconds every once in a while.

"The moon is still too close to the earth, and it still rotates at Approx. 1000 miles per hour, indictating that it is not billlions of years old?"

The moon will not get further from Earth unless giant rocket thrusters are attached, because the moon far away has more potential energy than the moon close up. I don't know what you mean by the rotation at ~1k mph, unless you mean the moon's orbit around Earth, in which case I'll reiterate that as gravity systems gain entropy, they also gain heat (ie speed), but loose enough potential energy to obey conservation of energy quite flawlessly.

[Wyrm]

Gravitational systems defy normal intuitive understanding of entropy: as they decay the objects in the system speed up and appear to gain energy, but really they are losing the potential energy of seperation.

In terms of GR, any orbital system loses energy to gravitational radiation, so what you say is correct, and that if you waited for the Earth to tide-lock with the Moon and then left the system to its own devices, the Moon will spiral down toward the Earth, eventually. However, such effects that pull the Moon in are utterly insignificant compared to other effects that tend to push the moon away from the Earth.

As time goes on, the moon will get closer to Earth, not farther away.

False. For the time scale, masses and rotation rates we're talking about, gravity for the Earth-Moon system can be treated as a perfectly conservitive force, for which entropy has no meaning at all.

Here, you are forgetting the fact that the Earth rotates much faster than the Moon orbits, which is the chief reservoir of extra energy for the system. Kinematical systems with friction settle into motions with the most energy dissipated as heat, yet conserve linear momentum, angular momentum, and total energy. In the Earth-Moon system (neglecting the sun), this happens when the rate of rotation with the Earth matches the revolution of the Moon about the Earth, which will match rotation rate of the Moon. Ie, when the Earth completes one rotation about its axis in the same time the Moon completes one revolution about the Earth.

Since the Moon's orbit is about 29 days, obviously the Earth turns faster than the Moon orbits. Study the figure 3 of this page. Notice that, because the Earth turns faster, the bulge of water gets ahead of the moon. The extra mass of the water applies a force component perpendicular to the lever arm: the water applies a torque to the Moon to increase the angular momentum of the Moon's orbit. At the same time, the Moon exherts a counter-torque on the water, which is in frictional contact with the Earth, resulting in the (current!) slowdown 0.0016 second/century in the Earth's rotation.

The friction between the water and the Earth results in heat, which is dissipated in the normal way. Meanwhile, the Moon's revolution has been given a bit of energy and angular momentum, so its orbit grows larger, and the Moon receeds.

Therefore, the increase in the total orbital energy of the Moon is compensated by much larger decrease in the rotational energy of the Earth. Entropy comes in as the excess rotational energy is dissipated as heat through friction.

However, in regards to vargo's question, there is very good reason to believe that the rate of tidal slowdown is unusually high, due to the fact that the tidal force and the response function of the oceans are near resonance, so this slowdown is unusual, and in the past much lower. Even if there wasn't, and the slowdown is typical, the recession rate is consistent with the orbital distance to the moon.

[Sriad]

Ah, ok. I haven't learned as much about planetary orbital systems as stellor, so I wasn't aware of the tidal torque force moving energy to the moon; I was only thinking in terms of Earth's rotation slowing as a function of heat lost in tidal friction.

Learn something new every day.

[Kuroneko]

Gravitational systems defy normal intuitive understanding of entropy: as they decay the objects in the system speed up and appear to gain energy, but really they are losing the potential energy of seperation.

In terms of GR, any orbital system loses energy to gravitational radiation, ... . However, such effects that pull the Moon in are utterly insignificant compared to other effects that tend to push the moon away from the Earth.

You're right, but I don't think that's what he is referring to. He's actually right about entropy in gravitationally-bound systems; the problem is that it doesn't mean what he thinks it means (those kinds of considerations are only negligibly applicable here, as you point out later). One the better examples is star formation. If a cloud is hot enough, it will not collapse because its thermal pressure balances its own gravity. As the cloud radiates away energy, it starts collapsing, but compressing gases raises the temperature. The end result is that the cloud radiates away energy and its temperature increases. In thermodynamic terms, gravitationally-dominated systems have a negative heat capacity: putting energy into them cools them, while taking energy out heats them. From a thermodynamic point of view, this almost looks like utter nonsense... until gravitational potential energy is accounted for.

[Wyrm]

Ah, yes, the Kelvin-Helmholtz process. It was never put to me in those terms, so I didn't realize the connection.

And the teacher becomes the student, although the previous student did not become the teacher.

[Darth Wong]

If the earth was billions of years old, the moon would be much farther away from the earth than it is, and its gently slowing rotation would have reached zero, The moon is still too close to the earth, and it still rotates at Approx. 1000 miles per hour, indictating that it is not billlions of years old??

Let me guess where you heard about this: a creationist website.

[vargo]

If the earth was billions of years old, the moon would be much farther away from the earth than it is, and its gently slowing rotation would have reached zero, The moon is still too close to the earth, and it still rotates at Approx. 1000 miles per hour, indictating that it is not billlions of years old??

Let me guess where you heard about this: a creationist website.

My science teacher who happens to be very religous I think. I was stumped when she said it and I'm trying to find ways to understand what she ment. I wanted to disagree with her, But I need to know what she said is correct.

[Darth Wong]

If the earth was billions of years old, the moon would be much farther away from the earth than it is, and its gently slowing rotation would have reached zero, The moon is still too close to the earth, and it still rotates at Approx. 1000 miles per hour, indictating that it is not billlions of years old??

Let me guess where you heard about this: a creationist website.

My science teacher who happens to be very religous I think. I was stumped when she said it and I'm trying to find ways to understand what she ment. I wanted to disagree with her, But I need to know what she said is correct.

Ask her to provide the base astrophysics data which she used in order to come to this conclusion, so you can present it to other people you know who can confirm her calculations. Watch her twitch.