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Why Don’t Celestial Bodies “Fall” into the Sun?

If gravity was simply the attractive force of  bodies, with mass being the most influential factor, why would bodies in the “solar system” not be drawn into the Sun?

NASA answers this question as follows:

“Why is it so difficult? The answer lies in the same fact that keeps Earth from plunging into the Sun: Our planet is traveling very fast — about 67,000 miles per hour — almost entirely sideways relative to the Sun. The only way to get to the Sun is to cancel that sideways motion.”1

So, the reason why the earth, under the influence of the gravitation “pull” of the Sun, is because it has great “sideways” velocity. The earth is, supposedly, travelling 67,000 mph.

I’d like to make an objection.

If the earth had an initial velocity, that velocity would be in a certain direction. For the earth to revolve around the sun, the sun would need to be able cause that velocity to change 180 degrees to move around the opposite side of the sun.

How could the sun have the power to constantly reverse the lateral velocity of the earth, but never move the earth towards itself?

It would make sense why a high velocity body might move, in one direction, past the sun, but that’s not what the earth does according to the heliocentric model. Rather, the earth passes by the sun in one direction and the sun completely reverses its momentum, and then reverses it again–but doesn’t move the earth towards the sun because the “sideways velocity” is too great.

That explanation makes absolutely no sense for a revolving object–unless, of course, I’m just crazy.

Moreover, since the earth does not generate its own velocity but is said to continue in motion as a result of an initial velocity, wouldn’t the sun actually have to be the cause of its velocity in the opposite direction, since the earth’s initial velocity had been lost?

When I played baseball, I was a pitcher, and catcher when not pitching. When I caught a ball thrown 90 mph and then threw it back to the pitcher, I never imagined the ball’s velocity on its way back to the pictcher to be its intial velocity.

Then, again, I’m not a heliocentric astrophysicist, so my understanding of baseball could be wrong and I could be giving catchers way too much credit.

WCM

  1. “Source: “It’s Surprisingly Hard to Go to the Sun”. NASA, 2018. https://www.nasa.gov/solar-system/its-surprisingly-hard-to-go-to-the-sun/#:~:text=Why%20is%20it%20so%20difficult,to%20cancel%20that%20sideways%20motion. []

8 Comments

  1. Roy Roy April 15, 2024

    I’m definitely no astrophysicist but I do have some knowledge of these things from schooling and stubborn research. I believe your probing boils down to investigating the concept of circular motion as understood in modern physics. Which is derived from Newton’s laws of motion.
    So it goes. The velocity of a rotating body is tangential to the circumference of its rotation. This means the velocity is continually changing direction. What causes this changing velocity? A centrally pointing force, which in the case of the earth and the Sun is asserted to be gravity.
    The analogy they use is: Imagine a ball on a string. If you first get the ball spinning and then cut the string (which represents gravity), it will fly off tangentially in a straight line.
    However, this analogy simply begs the question – what is this invisible spinning hand? Why is the Earth moving in a straight line to begin with? They are forced to appeal to some arbitrary original motion, which is not scientific.
    On the contrary, I believe Aristotle divides natural motion into linear (which is found among earthly bodies) and circular (which is found among heavenly bodies). I’m like you, I can’t see how you can arrive at circular motion from purely linear motion.
    Finally, Newton himself knew that this concept of a stationary Sun and a rotating Earth was false. Since every object is subject to gravity, the Sun itself is rotating, so too is the Moon and everything else in the Universe. Newton grappled with the so called 3-body problem, trying to calculate why it is the Sun, Moon, and Earth maintain a stable dance-like orbit (neither without colliding, or spiraling into space). He failed. Even today this problem is unsolved, and it is known to have no analytical solution. And that is just 3 bodies.

    • William C. Michael, O.P. William C. Michael, O.P. Post author | April 15, 2024

      You’ve provided the norma high school illustration of the idea, but it really doesn’t answer the question. A satellite stays in by use of an engine that constantly drives it away from the planet. It is not kept in orbit by its initial velocity.

  2. Jared Haselbarth Jared Haselbarth April 16, 2024

    It seems to me that in order for orbit to take place, there would have to be from the very start the exact present speed of the earth and the exact distance between the earth and the sun. Any deviation from this exactness should’ve cause the earth to fall to the sun or more likely keep going past the sun in the straight line it was going, maybe with a slight change of direction.

    Newton making it a law that all motion is straight unless acted upon seems to make it impossible for anything to become “in orbit”. NASA and scientists say that “eventually” moons will crash into their planets, or planets into their suns….it just takes millions of years. This is never actually observed, it’s only speculated.

    Why should the law be that all motion is naturally straight? What is the basis for that? Wouldn’t that depend on the nature of the mover? Everything seems to be in orbit, yet Newton says that natural movement is straight. Besides, a more recent idea is that space/time is curved, and so things which appear “in orbit” are actually just going in a straight line, it is space that is bending. https://youtu.be/wrwgIjBUYVc?si=zkoyj0H7-BlA8UPe&t=640

    There are so many questions that are left unanswered. What about that they posit that the Sun is moving at 450,000 miles per hour…in an orbit?

  3. Jared Haselbarth Jared Haselbarth April 16, 2024

    Another curious point here. How do we calculate the mass of an object in space? NASA says this is done by observing how long it takes nearby bodies to orbit that object, given that you know the distance between the two! Isn’t that circular? Do we know any of the initial data? How do we know gravity is a relationship of the given masses of objects? We don’t know the masses of any of the objects or their distances.

    What if earth has the greatest mass? Their answer would be…well then everything would be orbiting earth.

    • William C. Michael, O.P. William C. Michael, O.P. Post author | April 16, 2024

      This gets back to the issue I raised the other day about what “downward” means in Einstein’s theory of gravity. “Mass” assumes gravity. The strength of gravity would be quantified in terms of “mass”. On earth, we understand “gravity” just means motion towards the center of the earth, but in space? It makes no sense.

      I know we’re all supposed to assume that all of these questions are answered, but if you ask, you will never find anyone who knows the answers. Yet, they’re all asserting the ideas and appealing to some unknown prover.

      • Jared Haselbarth Jared Haselbarth April 17, 2024

        Yes, “Mass” assumes gravity.

        To calculate the mass and distances of objects in space, we…use the mathematical formula of theory of gravity. To calculate the gravitational force of objects in space, we use their mass and distance.

  4. Jared Haselbarth Jared Haselbarth April 23, 2024

    Bill,
    I was thinking about this again today, because it seems to raise so many questions.

    First, it seems that the only way something might possibly go into “orbit” is if the body orbiting originated from the body it orbits. For instance, we can see how satellites orbit the earth, but they were launched apparently with the same orbital velocity as the earth. Even so, these satellites eventually fall to earth if they are not occasionally sped up, as I think you’ve mentioned. For a body to attain orbital motion relative to another body appears to be impossible given modern physics. This is, I think, the point of your post. How would any body attain an orbital motion around another body if it wasn’t already doing so? No modern physics appears able to account for that.

    Secondly, Newton’s first law of motion is “a body at rest will remain at rest unless an outside force acts on it, and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force.”
    What do they mean “outside force”? If one says, well, like another body moving towards it, that is an outside force. But, in the second part of this law, an object in motion is not an outside force, but another object not being influenced by any outside force. Sal Khan for instance says “A force is not required to keep an object in motion.” When the two bodies come near each other, the one at rest and the one in motion, which one is the outside force and which is the object remaining in its present state? Each are uninfluenced bodies considered as a subject relative to the other, and each are the thing influenced by outside forces when considered as the object of the other. This law does not seem to make any sense.

    Further, how can Newton account for the movement of his own body? What force is the cause of the movement of his body at rest? We can say, muscles. But what moves the muscles? Nerve cells. What those? The “outside force” in the case of one’s body is obviously the intellect, a thing non-corporeal. How could it not also be the case for bodies moving in space that the outside force is non-corporeal, something Aristotle I would think would say is its “nature”.

    • William C. Michael, O.P. William C. Michael, O.P. Post author | April 23, 2024

      Yes, the modern “materialists” are trying to come up with an explanation other than Aristotle’s “Nature”, which is equivalent to the Christian’s “Providence”. Modern science (i.e., philosophy) begins with two unjustified assumptions, namely: (1) all causes in the material world are knowable, and (2) all causes in the material world are material.

      After those assumptions are received (by faith), all the theories and laws are attempts to explain these assumed material causes. These assumptions are not tested, but used as premises upon which to build the next set of arguments and this continues, endlessly.

      The fundamental challenge, in my opinion, is that an object “in orbit” is constantly changing in velocity. Any Physics textbook will explain that “Velocity is a vector quantity that describes the speed and direction of an object.” It is not merely a measure of speed, but of speed AND direction. Thus, the “velocity” of a body moving at one time in one direction, and at another time in another direction, is not constant. To be so, the object would need to continue moving in the same direction.

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