Weightless is a misnomer

micro gravity is more appropriate

first weight is the pull of gravity, on or near Earth it pulls mass toward the center of Mass for the system,

in orbit that pull still is present it just presents as a constant change in motion(ie acceleration) whose vector carries it in a path around the CoM, In a car going around a corner you inertia wants to keep you and the car in alignment with the motion vector of the car a force applied by the tires to the wheels to the chassis to the seats to your body and eventually to your neck is indistinguishable from the pull of gravity except for it's direction

when falling the same applies, there is a gravitational pull, but here here the motion vector is more closely aligned w/ the acceleration vector, the less alignment the more sideways motion

In a descending elevator the force of gravity is reduced by the acceleration of the elevator, if it accelerated own at 9.8m/s2 then you would feel no weight(till you hit bottom where the neg accel hits all at once making you weigh tons for a micro sec)

similarly when going up on the elevator the acceleration of the elevator adds to the pull of gravity causing increased weight on your legs

These inertial forces are all indistinguishable from the force caused by gravity except for the mechanism and vector

[QUOTE=island911;11898316]Do I?

.....
Your explanation of how F_g=mg=ma (g=a) "is backwards" seems a bit non sequitur and does not flip these relationships. Not even in Newtonian physics.

A..[/QUOTE}

F_g=mg
is just a mathematical relation between 3 things
F_g is a subset of all other forces in that it specifically names the force caused by gravity, aka weight

mass is the affected mass

g is the local acceleration caused by the local gravitational field, which for a planet varies w/ height and specifics to your location there are many causes for g to vary local mass concentrations contribute as well as the inertial spin forces which lower g at the equator of the Earth to 9.76 m/s² and to 9.83 m/s² at the poles

F = ma is just the more generalized superset that describes the effect of any force on a given mass

It does not specify the source of a force only its effect on one particular thing


it could correctly be written

m = f/a or a = F/m

Wait, you previously (scolding) said it was backwards and that I should go back to school for a refresher for calling gravity (g) an acceleration.

Nice to see you come around on that.

I get that people call out centrifugal force as a force, even though it is not a force. Yet it is handy to have that relative reference frame.

But what is this about inertial spin at the equator changing the gravitational (or space-time) field?

Seems an asteroid pulled into a pole or the equator would 'see' the same planetary mass-induced acceleration.

No?

I set off a maelstrom of nerdiness!

Gravity has always been described as the weak force, IIRC.

Right Bill?

That is string theory.

Seems Bill prefers his gravity loopy.

:)

no sir
Gravity, capitol g is a force

little g in Newton's second law quoted in your post is the acceleration caused by Gravity, capitol G

This is why I chose chemistry instead of physics.

This is why I chose lithography instead of physics and chemistry.

again don't confuse forces and accelerations

any change of motion can only be caused by a force,

change of motion aka acceleration can be speeding up, slowing down or changing direction

net acceleration is always in the same direction as and proportional to net force applied

net force is the summation of all the forces acting on the body

the force between the asteroid you mention and Earth is defined by this formula
F = Gm₁m₂/r²

F is the force acting to pull the 2 masses together
G is the universal gravitational constant
m₁ is the Earth's mass here or any other generic mass
m₂ is the asteroids mass here or any other generic mass
r is the distance between the gravitational centers of the 2 masses, which in the case of a homogeneous masses is also their geometric center

That formula also applies to the person standing at the N pole or at the equator, but that is not the only force being applied to a person standing on the surface of the Earth, Such a person is also having the direction of his motion continuously being changed by an additional force, in this case the friction( + less important forces like air resistance) between the person and the surface he/she is standing on. The net Force applied is the summation of all the forces being applied and again will be aligned the direction of the summation

In the case of the person on the equator there is a considerable change in the direction of motion, w/o G the person would continue to go in a straight line at ~460 m/s soon leaving the Earth on a tangent, w/o friction the person would be stationary and slam in to any any on coming vertical surface connected to the Earth at ~ 450m/s, The summation of all the forces keep the person planted moving along at ~450 m/s w/ a path the curves parallel to the Earths surface

as one approaches either pole the spin velocity of the Earth's surface asymptotically approaches 0, so the net acceleration asymptotically approaches g caused by G(capitol G, Earths force gravity) and the person's weight adjusts correspondingly

The analogy of a car going around a curve is apt, w/o a force to change direction, the car or you will go straight off the road, the tires generate a friction force(the basis of which is mostly electro-magnetic force, remember there are only 4 fundamental forces) this additional force alters the straight line inertia(aka momentum) to change the direction of motion. You as a passenger cannot sense any difference between this phantom inertial force and gravity other than the direction of action

Bill- are you a physicist or scientist?

Bill, I'm not confusing forces and accelerations. Did you watch the vid I posted?

I also get all that you posted.

BTW, "spin velocity" is not the best wording as the spin at the pole is actually the same as the spin for an Ecuadorian (1rotation/day).

Of course the Ecuadorian has a curvelinear path that contains both translation and angular rotation (spin) whereas the Santa has only spin.

IOW- curvelinear translation goes to zero, not the spin.

This is why I chose astrophysics instead of lithography, chemistry and physics. :p


I'm not going to get into the semantic mishmash about forces, but I'll go back to the original question.

There is not a "center" on the Universe, which things are expanding away from. I know that's a bit non-intuitive at first, but think of this...

Imaging a large rubber band. Maybe, 10 miles across? Now, put a few ants on the rubber band. Each can see other ants along the band, maybe they can see how far other ants are because there's pen marks al around the band. So, ants have some sense of space, and distance.

Now, you, as a malevolent god, pull on the rubber band, stretching it. EVERY ant will see EVERY other ant moving away from them. Naturally, EVERY ant will look at that and say "if every single other ant is moving away from me, I must have some special place in the Universe, the center of expansion!". However, every single ant can say that, and therefore, they do NOT have any special place, by definition. The problem comes from the fact that the rubber band is a 1 dimensional world expanding in the second dimension, and that makes it SEEM like every single ant is at the center of expansion. In fact, none are, and the rubber band Universe is far more complex than the ants think it is.


We are in a 3 dimensional Universe which is expanding in the 4th dimension. Every single spec of dust in our Universe sees everything moving away from it, and therefore makes the logical mistake that they are at the center of expansion, which is false.

So, no center of expansion of the Universe, therefore, no point at the center where gravity goes to zero simply because of being at the center.

OK, to answer post #22, it is hot down there. I know, because I'm a geologist.

Al Gore says it is millions of degrees. ;)

The Big Bang Theory says the universe exploded outward in all directions from a single point, but according to Mike there is no ‘center’ of the universe so the BBT doesn’t hold up?

No, the big bang theory says that we are in a 4 dimensional spacetime region, and we are seeing 3 dimensions of it. That region expanded from a quantum fluctuation in the primordial Higgs field, which crested over the Mexican hat potential barrier and then rolled down the potential well, expanding in 4 dimensions. The expansion was rapid (many times faster than the speed of light) for several seconds, which was called the Inflationary Era. Then, the total energy density of the Universe dropped enough for matter decoupling, which was the moment that the energy soup shattered into matter and photons. The photons have been traveling around ever since, and are seen as the Cosmic Background Radiation. Matter has been expanding into the 4th dimensions ever since, which is the Hubble expansion that we see with telescopes.

Wild thought, for brains more informed than mine:
Would the concept of gravity, and all things exhibiting it, be explained if everything was, at one time, a solid mass? Some force blew it apart, and gravity is the force being exhibited because the mass is trying to get back to the form it once had?

angular velocity is the same at the poles and equator, instantaneous linear velocity(spin velocity, because the instantaneous v is accelerated into a curve following the arc of the earths surface) is not. At sea level at the equator, your instantaneous linear velocity is ~460 m/s on top of a mountain on the equator it is a bit faster. This is why the preferred orbital launch direction is to the east and the preferred location is a mountain top on the equator, Kilimanjaro or somewhere in the Andes , like Quito

Oh yeah! I forgot about the Mexican hat potential. Things are gonna get really weird because we are definitely in another Inflation Era. It’s amazing how everything is connected!

string theory posits 10 dimensional spacetime, 9 physical and 1 time, the 9 physical ones are the 3 we are familiar w/ and 6 curled up ones that are needed for consistency w/ the reality we observe unfortunately there are 5 viable versions of string theory.

all 5 can be contained in an 11 dimensional mathematical construct called M Theory

one of the really fascinating things explained w/ all these extra dimensions is the conundrum of the disparity of the strengths of the 4 fundamental forces,

gravity @ 10^-64 of the strength of the E-M force is a real outlier.

one of modern Physics main goals is a Theory that unifies all 4 fundamental forces into 1

Electro-magnetic and Weak have been successfully unified, M Theory looks to be one of the better theories to unify the Strong and Gravity w/ Electro Weak forces

I've always gotten a kick out of how time and space moved thru... wait, what did space move into faster than the speed of light? And did this for how long? ;)

Yeah, I get all of that, and know that you understand that too.

It's just that how you had written that point prior was ambiguous if not confusing (backwards?) for the typical reader.

It may be that our apelike brain is not yet sufficiently developed to cope with the reality of the universe......yet.

It’s definitely shorts and flashlight weather down there. One of those scarves you soak in cold water is worthwhile, too.

Space was not moving INTO anything. The anything ITSELF was what was expanding. It wasn't a case of an existing region, and the Universe was just taking up a larger section of it. There was no region, all of "region" was bundled up into the thing that was expanding. So, therefore, there is nothing "outside" of space, there was no pre-existing "thing" that space moved into, and no need for a prime mover. ;) wink back at you.

As for faster than light, things cannot move faster than light though spacetime. Spacetime ITSELF has no such restrictions. The only problem with spacetime expansion is that information is lost when two sections of spacetime expand away faster than the speed of light...there was no communication across the Universe when Inflation happened. This was part of the decoupling, and why we cannot talk about what is beyond the Visible edge to the Universe. There's stuff out there, but any information has been lost between it and us, since spacetime stretched faster than light between it and us.

I might wear long pants...my legs burn easily.

This is the part that makes my head hurt. It's difficult to visualize space being the entirety of existence with no borders up against anything else. I accept the red shift of the universe but how can it expand into nothing thereby creating more of something?
I'm accustomed to a finite existence. For the universe to expand my mind says that it must expand into another space or dimension.

As stated my ape brain is better at defining the limits that I will work within whether it be confidence limits or an LoQ specification.

I thought we just discovered that gravity waves also move at speed of light - which is just space moving right?

I played this through in my head a few times and don't see why expansion had to be faster than C. Do you happen to have a thought experiment handy that explains why its necessary that expansion happened at more than c?

OK. Think of it this way, flatty.

You are in a room with furniture, lights, floor. A typical room. You know you are in a room because your body is sending information to your brain which interprets what your body is sensing. Information. Sounds, smells, images, temperature, even the passage of time, etc. Now as man has developed, our ability to gather information has expanded. Suddenly we can see further with a spyglass and see smaller with a magnifying glass. We can measure time and temperatures way beyond what we’ve ever imagined. Our ability to gather information grows. So now we are able to receive information beyond our own bodies’ abilities. We can detect electromagnetic radiation, magnetism, x-rays, infinite degrees of wavelengths of light, and so on.

Now imagine a place where there is no information. Not information that is out there that we don’t know how to receive yet. But rather no information. No gravity, no light, no radiation, no time, even. No nothing. There is nothing to be detected and no amount of technological advances can ever be able to detect it. Even if our most powerful telescope was on the edge of our known universe looking into space it would see nothing. There is nothing to see. There is no information. Just space without limit.

That is what the universe is expanding into.

Yeah, I wasn't trying to suggest a prime mover of some sort.

I mean that's just not believable.

Obviously... there was nothing, and then it exploded. ;)


https://media3.giphy.com/media/mrn71...giphy.gif&ct=g

;)

We cannot visualize it at all, but mathematically it all makes sense. 4 dimensional spacetime, and we are a 3 dimensional universe within it. Dots drawn on the surface of a balloon (3D spacetime, 2D universe) all see the other dots moving away as the balloon expands, but none of them can calculate the size of the 2D universe, nor the edge of the 2D universe, nor the center of the 2D universe. Their 2D minds and basic geometry simply won't let them see or understand that their 2D universe is wrapped around a 3D object.

We are a 3D universe wrapped in 4 dimensions. We cannot see the edge, cannot find the center, nor can we determine the size of the universe, but it is still finite in size, and expanding in a mathematically understandably way.

Inflation didn't HAVE to happen, but it did happen. That flattened the Universe (make a circle, then make the circle REALLY BIG, and the surface starts to appear flat, not curved). Inflation make the Universe appear flat, not curved. It made the somewhat chaotic stew of matter very homogeneous, since quantum fluctuations which might have appeared as very high density regions got smeared apart under inflation. The distribution of matter that because galaxies and such was spread so thin, that it is now basically equal in every direction.

There was the Higg's Field. That's not nothing, it was an energy field of negative potential energy that had a high enough value to spawn the Universe. How can you call that nothing?

;)

Wait wait... you just said there was no pre-existing "thing" that space moved into

Space and time didn't exist before the Big Bang. There was simply nothing before that event.

n'no, there was Higg's field all the way down. :cool: (a little reference to the elephant tortoise explanation.)

It does not matter what any creation theory one prefers of the nearly infinite creation stories that every single group of people have. There was always a mysterious and un-explainable beginning. If you believe some entity was the creator, where did that entity come from? What created it? Same issue for all creation theories. With the current big bang theory, that there just was nothing before, as space and time did not yet exist. For all of human existence we have asked where did I come from, and where did the Earth and the stars come from.

The big bang is the only one with any math and physics to try to explain it, but the physics of the first few trillionths of a second all break down. No one has yet figured it all out with math. There is no way to test the theory. No one can say with any real proof one is the "Truth" and it all comes down to faith in math or the mystical. You get to chose what best fits your views.

https://upload.wikimedia.org/wikiped...00_no_WMAP.jpg

The inflationary period is when the Universe expanded faster than the speed of light, causing local domains to lose contact w/ each other. We live in one such domain referred to as the observable universe as opposed to the total universe.


Things pop into andout of existence all the time.

It's called Random Quantum Fluctuation

https://upload.wikimedia.org/wikiped...uctuations.gif

In quantum physics, a quantum fluctuation (also known as a vacuum state fluctuation or vacuum fluctuation) is the temporary random change in the amount of energy in a point in space, as prescribed by Werner Heisenberg's uncertainty principle. They are minute random fluctuations in the values of the fields which represent elementary particles, such as electric and magnetic fields which represent the electromagnetic force carried by photons, W and Z fields which carry the weak force, and gluon fields which carry the strong force. Vacuum fluctuations appear as virtual particles, which are always created in particle–antiparticle pairs. Since they are created spontaneously without a source of energy, vacuum fluctuations and virtual particles are said to violate the conservation of energy. This is theoretically allowable because the particles annihilate each other within a time limit determined by the uncertainty principle so they are not directly observable.

usually

one place they do become real is at the event horizon of a black hole, where 1/2 of the virtual pair escapes and the other 1/2 is absorbed into the black hole, This observable effect is called Hawking Radiation and eventually leads to the total evaporation of the back hole.

One Theory of the Big Bang is that it is at least similar in nature to such a quantum fluctuation.

Ok. So if all physical laws break down at the quantum level, doesn’t that mean that something other than what can be described by physical laws happened?

What does one call something that happens outside physical laws?

The many Universes Theory posits multiple universes each of which may have it's own unique laws

In our universe based on what we know now there are 26 constants that define the universe
https://imageio.forbes.com/blogs-ima...=jpg&width=960

If any of these are the least different it changes the entire universe and other universes can have different values

So are you suggesting, Bill, that because there may be multiple universes is cause enough to conclude ours doesn’t exist? This universe, the one we live in, appears to be the result of something outside this universe’s (the one we live in) physical laws.

The multiverse theory looks to me to be a clever way to rationalize the inability of quantum physics to explain how we got here. Here, in the universe we live in.

Even then, since we are talking theory, what if all those other universes also appeared from their own definitions of nothing?