Dark Light Does Not Endanger Grandfather

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />Taking one detail here-does a body falling in a gravity field gain kinetic energy? The reason I ask is all orbiting bodies are falling. And yet there seems to be no gain in energy.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">All orbiting bodies are accelerating, but not necessarily "falling".

When there is one dominant mass such as the Sun, bodies in orbit around it have constant energy at all times. For a circular orbit, both kinetic and potential energy are each constant.

In elliptical motion (the norm), planets give up potential energy and gain kinetic energy as they get closer to the Sun, and reverse that process as they pull away again. The total energy (potential plus kinetic) always remains constant. -|Tom|-

You have stated kepler's laws in different words here but the Earth is being accelerated toward the sun. Why does this not generate energy over and above those laws?
Kepler's laws remain at the center of all the things that have gone wrong in astronomy-or so it seems to me. The sun is 99.9% of the mass in the model and so its OK to assume the sun's center is the center of mass but that is not true of the universe. The BB model assumes centers of mass exist in the universe too. How does the MM explain centers of mass?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />the Earth is being accelerated toward the sun. Why does this not generate energy over and above those laws?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Why do you associate "acceleration" with "energy gain"? If we throw a ball straight up, it is accelerating toward the Earth but not gaining energy in the sense you seem to imply (kinetic energy).

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The sun is 99.9% of the mass in the model and so its OK to assume the sun's center is the center of mass<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Only as a crude first approximation. The solar system barycenter is sometimes outside the Sun's physical body.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The BB model assumes centers of mass exist in the universe too.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Not to my knowledge. The BB specifically denies that any place in the universe is special or qualifies as a "center".

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">How does the MM explain centers of mass?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">MM explains them for what they are: mathematical fictions that are sometimes useful in models.

For example, if we consider a closed system consisting of the Sun and its planets, we have a certain center of mass. If we discover a new planet, that center of mass shifts, perhaps greatly. If we include Alpha Centauri in our closed system, the center of mass shifts half-way there. But none of these choices have any physical significance -- only mathematical significance. -|Tom|-

Earth is accelerated by the force of gravity-right? Force changes the path of the Earth from what it would be, isn't there reason to wonder if energy is required? In the universe mass is centered at billions of points. Would that render Kepler's laws useless in figuring out motion in structures like star clusters, galaxies and anything larger yet? It seems to me the BB model assumes what you call the barycenter is a mass center even though no mass exists at that center. Does this assumption also exist in the MM? In a galatic structure, for example, there is no other reason to make assumptions about mass existing at the geometric center.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />Earth is accelerated by the force of gravity-right?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Right.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Force changes the path of the Earth from what it would be, isn't there reason to wonder if energy is required?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">I can't see how it would be useful to you to describe what causes orbital motion by using the energy concept. First, I'll explain what's wrong with thinking in terms of energy. Then I'll explain a more useful concept.

Consider the energy of a 1 kilogram baseball thrown at 30 meters/second. Its kinetic energy is defined as 1/2 m v^2, which works out to 450 kg-m^2/s^2 (staying is kg/m/s units). But that same baseball is traveling around the Sun at 30,000 m/s, which means the same baseball has an energy of 450,000,000 kg-m^2/s^2 from the Sun's viewpoint. So why can't we tap into the baseball's vast energy for use here on Earth?

The answer is that "energy" is another fictional concept used for mathematical convenience. It is not a real, physical property of any body in isolation. It is instead a measure of how much work that body could do if it encountered some other body. But an orbiting baseball or planet is not encountering any other body, so the amount of work it could do is not useful information for understanding its orbit.

The properties that bodies of all sizes have that are physically meaningful and useful are LOCATION, MASS, and RELATIVE VELOCITY. And the concept that is most useful for describing why bodies orbit is MOMENTUM, which is simply the product of mass and relative velocity. For any body to affect any other body, it must either make contact with the other body directly, or send intermediaries to make contact with the other body. Either way, momentum is transfered from one body to another via the contact.

So if a single air molecule hits a wall, a tiny amount of momentum is transferred. But that is normally balanced by other air molecules hitting from other directions. OTOH, if many air molecules traveling in the same direction hit the wall, that "wind" produces a force against the wall that could eventually blow it over. FORCE is just the time rate of change of momentum as many momentum transfers are continually occuring in any situation.

In MM, the reason gravity exists is because innumerable tiny, ultra-fast "gravitons" are striking bodies everywhere, transferring their momentum and creating a force. The Earth orbits the Sun because gravitons striking Earth on its nightside always outnumber gravitons striking Earth on its dayside because the Sun blocks some gravitons that would otherwise have struck Earth's dayside.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">In the universe mass is centered at billions of points. Would that render Kepler's laws useless in figuring out motion in structures like star clusters, galaxies and anything larger yet?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Pretty much, yes. The same kinds of forces are acting between bodies, so more complicated laws (called "virial laws") replace Kepler's laws in clusters.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">It seems to me the BB model assumes what you call the barycenter is a mass center even though no mass exists at that center.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">??? There is no center of any kind in BB. Remember, BB is NOT a one-time explosion of matter into pre-existing space. (That would have a center.) Instead, it is an on-going creation of new space between all existing masses. So masses at rest get farther apart without moving because of the new space created between them.

There is also no edge either, so there is not even a geometric center. Every body in the BB universe sees an equal number of other bodies in any direction it looks.

If you don't like that theory, most of us think MM is your best alternative.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Does this assumption also exist in the MM?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">In MM, the universe is infinite, and there is no center to infinity.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">In a galatic structure, for example, there is no other reason to make assumptions about mass existing at the geometric center.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Single galaxies do have their greatest mass concentration at their centers. Perhaps you mean clusters of galaxies, which may easily have nothing at their geometric center? But with forces viewed as accumulated momentum transfers, there is no reason why centers should be important. -|Tom|-

These concepts always get too big to grasp after a few posts-anyway every star is a mass center and they are assembled is structures like clusters and disks in a way that no mass is at the geometric or barycenter. All the mass of the disk is in the individual stars. How can the major part of the total mass be be located at the center of the disk?