The Science Thread here

reply to post by Arbitrageur


If gravity is a stronger force then dark matter, in the early stages of the universe when there was less space then energy/matter therefore less dark energy associated with that space, why didnt gravity keep the universe from inflating and expanding?

reply to post by ImaFungi

I'm assuming you meant dark energy and not dark matter.

There's a theory but it's not confirmed, and probably won't be unless we can create something closer to big bang conditions than we currently are capable of:

The inflaton is a hypothetical scalar field (and its associated particle) that may be responsible for the hypothetical inflation in the very early universe.

Apparently that would have been far more powerful than gravity.

reply to post by Arbitrageur


Yes that was a typo, my bad.

So in the beginning before the big bang, there was only one kind of energy/field/particle type (or were there none?)? And then right when the big bang began there existed different types of particles/fields, what caused the different ones to exist? So the inflation field, is energy that cannot do anything but...cause space to inflate?

reply to post by ImaFungi

It's hard to say. There are models, but since we don't have the capability to confirm them in experiment since we are unable to create big bang conditions, they can rightfully be called somewhat speculative.

Here is a wiki article describing some of the speculative ideas, though the further after the big bang, probably the less speculative the ideas, as the physical laws would more closely resemble what we observe today:

Chronology of the universe

The very earliest universe was so hot, or energetic, that initially no particles existed or could exist (except perhaps in the most fleeting sense), and the forces we see around us today were believed to be merged into one unified force. Space itself expanded during an inflationary epoch due to the immensity of the energies involved. Gradually the immense energies cooled - still to a temperature inconceivably hot compared to any we see around us now, but sufficiently to allow forces to gradually undergo symmetry breaking, a kind of repeated condensation from one status quo to another, leading finally to the separation of the strong force from the electroweak force and the first particles.

Also, if time began with the big bang as may be the case, the concept of "before the big bang" would have no meaning.

reply to post by siliconpsychosis


Centrifugal force actually isn't a component of gravity but can be used to create artificial gravity. Basically though, if our feet remaining stuck on the planet solely relied on centrifugal force, we would have been jettisoned off of it a long time ago as centrifugal force actually pushes outward and doesn't pull in. An example of centrifugal force would be the Gravitron ride at your local fair. When the Gravitron is going (which is basically a big centrifuge), you're pinioned like a fly on a windshield as the Gravitron accelerates in speed. That push is actually pushing you against the external wall of the Gravitron instead of sucking you in. How it's used to create artificial gravity is due to a combination of centrifugal force and linear acceleration.

What happens on the planet is a combination of gravity and centrifugal force. It basically represents an equilibrium where we aren't sucked into the ground or jettisoned off into space. What would happen if the earth stopped spinning? Well, that's a super cool question and here's a link where the actual experts answer it: www.esri.com...

Originally posted by Phage
reply to post by jiggerj

 

Sure. But coal is a lot cheaper.

And coal consumes a lot less energy to make it burn than a diamond does so it'd be likely to consume more energy to burn than it would produce.

To jiggerj: Diamonds are basically a very compact and rigid form of coal. A really basic comparison to this would be boiling water (though not technically right as liquid water turning to ice expands and coal turning into diamond actually compacts). The molecular structure of diamonds is more complex and rigid than coal and, likewise, the molecular structure of ice is more complex and rigid than water. The application of heat to all of those things creates the disintegration of bonds and releases energy. So if coal was water and ice were diamonds, the amount of energy that would be consumed to boil water would be less than the amount of energy consumed to boil ice as the molecular structure of the water would be less rigid with less bonds to break than the ice as the energy for boiling ice would initially require the addition of melting the ice to a liquid state before bringing it to a boil.

reply to post by WhiteAlice


Could the force of gravity simply be the result of the centrifugal force via the planets rotation, along with the velocity of the planets revolution?

Originally posted by ImaFungi
reply to post by WhiteAlice

 

Could the force of gravity simply be the result of the centrifugal force via the planets rotation, along with the velocity of the planets revolution?

So you're asking if the force that's pulling us inward is the result of the force that's pushing us outward? Does that question make sense even to you?

Originally posted by WhiteAlice
centrifugal force actually pushes outward and doesn't pull in.

Yes that's the apparent effect we observe. It makes us weigh a little less at the equator than at the poles. That was an interesting article about polar oceans if the Earth stopped spinning.
Also from the perspective of a physicist, there is no such thing as centrifugal force, which is why it's called a "fictitious force".
But for the purposes of discussion outside of physics we can refer to that as an apparent force.

Originally posted by Arbitrageur

Originally posted by ImaFungi
reply to post by WhiteAlice

 

Could the force of gravity simply be the result of the centrifugal force via the planets rotation, along with the velocity of the planets revolution?

So you're asking if the force that's pulling us inward is the result of the force that's pushing us outward? Does that question make sense even to you?

I think that what ImaFungi is asking is that if we can produce artificial gravity through the combination of centrifugal force and linear acceleration, then they are intending that the "revolution" being referred to isn't defined as the spin of the planet but the revolution of the planet around the sun possibly acting as a form of linear acceleration. That question actually popped into my head, too, when I was thinking about centrifugal force and linear acceleration as to whether or not there would be some increase to gravity on the planet that would be the result of that specific combo (spin and the movement around the sun). I know that both centripetal force and linear acceleration are both factors in what reproduces the earth's elliptical orbit around the sun but it goes well outside my basic knowledge of physics to know if any of the gravity on earth could be construed as a mechanism of those same two forces. Maybe somebody could attempt to answer that re-framed question for both of Ima and I?

Yes that's the apparent effect we observe. It makes us weigh a little less at the equator than at the poles. That was an interesting article about polar oceans if the Earth stopped spinning.
Also from the perspective of a physicist, there is no such thing as centrifugal force, which is why it's called a "fictitious force".
But for the purposes of discussion outside of physics we can refer to that as an apparent force.

edit on 22-6-2013 by Arbitrageur because: clarification

Yep, that's why I'd rather move to the equator to shed a little weight than suffer the restrictions of a diet. I find it really very curious that physicists actually consider it to be a fictitious force when it's something that is readily observable in things like a gravitron or a centrifuge or like the time that I tossed the slime that I made in chemistry into a fan to watch it all splatter everywhere (I was a curious kid, what can I say and for the record, the slime really flew lol though that was probably more of a ricochet process than taking an object in a set position from the center and spinning it). Looking at it, I see that the argument is that what is viewed as centrifugal force is considered to be centripetal force supplied by gravity. The question is then, what would happen if you took off the external walls on a Gravitron (NOT suggesting this as an actual experiment!). I imagine that people would probably just tumble off and fall to the ground as there would be nothing fixing them in place?

Originally posted by WhiteAlice
I think that what ImaFungi is asking is that if we can produce artificial gravity through the combination of centrifugal force and linear acceleration, then they are intending that the "revolution" being referred to isn't defined as the spin of the planet but the revolution of the planet around the sun possibly acting as a form of linear acceleration. That question actually popped into my head, too, when I was thinking about centrifugal force and linear acceleration as to whether or not there would be some increase to gravity on the planet that would be the result of that specific combo (spin and the movement around the sun). I know that both centripetal force and linear acceleration are both factors in what reproduces the earth's elliptical orbit around the sun but it goes well outside my basic knowledge of physics to know if any of the gravity on earth could be construed as a mechanism of those same two forces. Maybe somebody could attempt to answer that re-framed question for both of Ima and I?

That sounds nothing like Ima's question but let me try to rephrase what I think you're asking, which is, is there an apparent effect on Earth due to "centrifugal force" resulting from the Earth's orbit around the sun?

The answer is yes. In the summer consider day versus night. In the daytime, centrifugal force from Earth's orbit is in the same direction as gravity so your apparent weight would be a tad more. At night, centrifugal force from Earth's orbit is in the opposite direction as gravity so your apparent weight would be a tad less.

Looking at it, I see that the argument is that what is viewed as centrifugal force is considered to be centripetal force supplied by gravity.

Not exactly, because centripetal and centrifugal forces are in opposite directions, right? The fictitious centrifugal force is simply the result of inertia, if you remember the saying that "an object in motion tends to remain in motion", so that is how physicists actually see centrifugal force in physics models, as an inertial effect.

The question is then, what would happen if you took off the external walls on a Gravitron (NOT suggesting this as an actual experiment!). I imagine that people would probably just tumble off and fall to the ground as there would be nothing fixing them in place?

Again an object in motion will remain in motion unless acted upon by an outside force. With walls in place, there are two outside forces, gravity and forces applied by the walls.
With the walls removed, the only appreciable outside force is gravity, in which case it becomes a simple calculation as is done in ballistics, combining the falling motion due to gravity with the inertial motion, which results in a trajectory.

reply to post by Arbitrageur


WhiteAlice correctly interpreted my question. Which was; is the reason things stay on the body of earth (gravity) because of the earths rotation, coupled with (linear acceleration) the earths revolution around the sun? I understand it relates to inertia. The thing is I can understand the viable reality of Einstein space-time curving gravity, it really seems like the only possibility for how gravity works, but I dont get why its not then seen that space must then be some type of energy field that is malleable. Or is this known and discussed?

Also in a non violent way, if the earths linear acceleration and rotation were stopped (not immediately halted, but lets just say the earths motion was completely stopped, then all the things and people were place on its surface.) first of all, is this even theoretically possible in our universe for an object in space to be relatively motionless (not talking about all the molecular vibrations and such) compared to an absolutely motionless reference frame? Or do the dynamics of the universe, prod all objects to move, like a river of space and time? Or if in that scenario of stopping the earth, would it be inclined to 'fall' in a particular direction, or if there were no bodies that could lend their gravitational extent it wouldnt fall at all? But the earth supposedly has its own gravity which is a distortion of space, and this distortion of space is what keeps all the things attached to earths surface? This is what I dont get really.

(And I have never been a proponent or researcher of electric universe theory; but is it possible gravity has to do with the electric and chemical bonds of the totality of matter of a body? the earth seems pretty solid, and this is due to the atomic bonds of the matter, if those bonds were all broken earth would no longer be a solid semi spherical body, but you are saying because of gravity, there is a chance the matter would be urged to all interact again and clump up, and the cause of this clumping is not the molecules and atoms themselves electrically or magnetically reaching for other matter and drawing it near, but because all the matter in an area is distorting space, and those distortions allow matter to with less of its own energy clump into other matter?)

Originally posted by ImaFungi
reply to post by Arbitrageur

 

WhiteAlice correctly interpreted my question. Which was; is the reason things stay on the body of earth (gravity) because of the earths rotation, coupled with (linear acceleration) the earths revolution around the sun? I understand it relates to inertia.

I thought the answer to this was too obvious which is why I ruled out this interpretation, but I guess it wasn't too obvious.

The reason things stay on the body of Earth is because of gravity. The Earth's rotation and revolution only add minor deviations to the apparent gravitational force, as do slight variations resulting from the gravitational pull from the sun and moon. All of those have only a fraction of a percent influence, so Earth's gravity is well over 99% the dominant reason we are attracted to Earth.

I think I already answered your other question, when someone asked if we could send a rocket/probe to be stationary (relative to the CMB). We don't have that rocket technology available, but if we did it, would be theoretically possible to do something like that.

reply to post by Arbitrageur


What is thought to be the mechanism of earths gravity? why/how do objects stay on earths surface? (you answer with the word gravity, but can you define what that word means or how it works, the most likely theory?

reply to post by ImaFungi

I wish I knew. That question is one of the reasons I studied physics, and I don't think I ever really found the answer I was looking for. Newton didn't really try to explain its origin, and Einstein's theory gives us more insights but I don't think the origin has really been fully explained, or if it has, someone besides me will have to answer. We can now say it "warps space-time" but then you could still ask "why does it warp space-time?"

There's an elusive topic called "quantum gravity". Perhaps if anybody ever develops a viable theory of quantum gravity or loop quantum gravity, I will finally get the answer I would like to have? Or maybe it will take a unified field theory or theory of everything if such a thing is even possible.

Quantum gravity (QG) is a field of theoretical physics that seeks to unify quantum mechanics, which describes three of the four known fundamental interactions, with general relativity, which describes the fourth fundamental interaction, gravity. The aim of quantum gravity is only to describe the quantum behavior of the gravitational field and should not be confused with the objective of unifying all fundamental interactions into a single mathematical framework. The two problems could be connected (as assumed in string theory) or could be separated (as assumed in loop quantum gravity).

The single mathematical framework would be a unified field theory (UFT). Einstein published some thoughts on such a UFT but I don't hear much about it, so apparently it wasn't useful like his theory of relativity.

reply to post by Arbitrageur


Hm, interesting, thanks.

About the 'warping space-time', I would more quickly ask; if space time is able to be warped, it must be something right?

It is thought that there are all sorts of 'fields' in/of space-time that are not made of atomic matter (higgs field for example, EM field too, potentially others too). So I personally really like the space warping Einstein idea, because I think its a physically viable explanation as to how an object can have a constant affect on another object at a relatively great distance, with relatively no sign of these 2 objects making physical contact with one another. To me it would then just seem like the energy density of space is lesser around a mass because of displacement, torquing, and warping compared to the energy density of space far from massive bodies, like in between galaxies. I would then say dark energy/spatial expansion/cosmological constant is the Yin to gravities yang, as gravity coalesces material closer and closer and causes those areas of displacement and less dense energy regions surrounding bodies, the other space in relation is subjected with more density.

so spatial expansion is the outgoing wave of gravity, and gravitational attraction is the ingoing wave.

I think gravity does have a lot to do with the motion and movement of bodies, rotation included. I think as earth travels through space around the sun it is creating a less dense pocket of space surrounding the earth, and this is its field of gravity. I think the earth rotating allows the extent of this less dense pocket of space to have a rotation of it, a spiral or spin, which aids the moon in revolving around the earth, and allows earth to have a gravitational extent in front of its path. If the earths rotation did not aid in this, I dont know how the earth could affect space infront of it it has not yet reached (im guessing this is why einstein thought space must be more like a fabric then a liquid or something, because if i drop a rock in the water it creates waves/rings that do travel in all directions, but if i were to move that rock a distance horizontally across the water, i dont think waves of energy will be equally extending in front of the rock as behind it...Back to dropping the rock however, the rings going out evenly in all directions, if the rock continued to fall after hitting the water with the same velocity, we can imagine its energy like the rings being projected evenly in all directions, and if the rock is spinning maybe even create a whirlpool, that if other objects were tossed in after it, would be inclined to orbit the rocks whirlpool path. So since it is said that because of gravity it is as if the earth is in free fall towards the sun, it could be like the rock falling into the water, creating a constant pocket of less density then what ultimately surrounds it, which can draw in other objects, to travel along the geometry of that pocket.)

A question. Is the sun held in orbit around the galaxy by the galaxies center black hole mass, or by all surrounding stars?

Originally posted by ImaFungi
About the 'warping space-time', I would more quickly ask; if space time is able to be warped, it must be something right?

Yes.

If the earths rotation did not aid in this, I dont know how the earth could affect space infront of it it has not yet reached

Gravity is thought to travel at the speed of light, so it should be no harder for the Earth to emit a gravitational field ahead of its path than for the sun to emit light ahead of its path. What about planets and moons that don't rotate or have slow rotation periods? Lots of moons are tidally locked. If there was a relationship between rotation and gravity it should be measurable, right?

Is the sun held in orbit around the galaxy by the galaxies center black hole mass, or by all surrounding stars?

Both. But hypothetical dark matter is thought to have a larger effect than either on the rotation of other galaxies. All objects in the galaxy interact gravitationally with each other, though obviously the strength of the interaction varies with mass and distance.

Originally posted by Arbitrageur
Yes.

Ok space must be something then. Are there any theories on what it may be?

Gravity is thought to travel at the speed of light, so it should be no harder for the Earth to emit a gravitational field ahead of its path than for the sun to emit light ahead of its path. What about planets and moons that don't rotate or have slow rotation periods? Lots of moons are tidally locked. If there was a relationship between rotation and gravity it should be measurable, right?

Gravity is thought to travel at the speed of light, thats very interesting. So maybe the reason light travels at the speed of light, and gravity (an aspect of space) travel at the speed of light are related to aspects of the nature of space (and of course energy I guess, but a combination of both to yield the final results and constants). Its not thought the space in the universe is an absolute or motionless space; its thought the big bang, cosmological constant (etc.) cause space to move, and of course mass causes space to move (gravity), so I wonder if there is an absolute 'grain' or motion to space outside of the gravitational extent of mass, and this absolute motion gets disrupted when mass is present and clashes, creating the potential for gravity.

About the sun emitting light ahead of its path, gravity is not some particle constantly shot out of all other particles to create an envelope in space (is this how light is imagined to be emit from the sun, like electrons shooting projectile like bullets? graviton theory is silly imo, it takes no effort to come up with that theory,(well we think everything that exists are particles or bits, and we dont really understand gravity, but thats probably particles too, oh and also nothing is really particles, everythings really waves, jk, everythings really fields, what are fields, well they dont really exist, and noone knows. So thats what is come up with? That every single subatomic particle even when its not emitting light, is constantly emitting particles at the speed of light (let me guess, infinite particles every smallest denomination of time) and the totality of these particles push all the space surrounding a mass out of the way?)

Is there a planet that doesnt rotate? Is there a planet that doesnt rotate with a moon? Is there a moon that doesnt rotate with a moon?

reply to post by Arbitrageur


Thanks!! I was thinking that inertia probably played a role but, as a visual based thinker, was getting dizzy trying to think about the subject of spinning and what if scenarios. Had to stop.

Originally posted by ImaFungi
Ok space must be something then. Are there any theories on what it may be?

Space is a different concept in relativity than in quantum mechanics. They don't really agree on exactly what it is which is why a theory of quantum gravity would be nice to have.

so I wonder if there is an absolute 'grain' or motion to space outside of the gravitational extent of mass, and this absolute motion gets disrupted when mass is present and clashes, creating the potential for gravity.

Well you do get "frame-dragging" around a rotating body. Even then you can't measure the movement of space, something has to be in the space and "dragged" by it to measure the tiny effect. But no luminiferous aether was ever found.

Is there a planet that doesnt rotate? Is there a planet that doesnt rotate with a moon? Is there a moon that doesnt rotate with a moon?

Wikipedia is a great source for looking this stuff up. As I said tidal locking is common. Ever notice the same side of the moon always faces Earth?

A day on Mercury is 2 Mercury years long, so it rotates, but not very fast.

Alright--this thread has gone pretty far off the deep end, so lets clear up a few random things from the last page or so.

Originally posted by ImaFungi
reply to post by Arbitrageur

 

If gravity is a stronger force then dark matter, in the early stages of the universe when there was less space then energy/matter therefore less dark energy associated with that space, why didnt gravity keep the universe from inflating and expanding?

Dark matter (and dark energy, for that matter) is not a force. It's stuff. It doesn't make sense to say thins like "if gravity is a stronger force than dark matter."

At any rate, in the very early universe the universe was expanding more quickly than gravity could pull things together. This is a standard part of the Lambda-CDM model of the universe, which has been confirmed experimentally to a very high degree of precision (and is theoretically very sound as well).

Originally posted by Arbitrageur
It's hard to say. There are models, but since we don't have the capability to confirm them in experiment since we are unable to create big bang conditions, they can rightfully be called somewhat speculative.

It's actually very easy to say, our models of the early universe are excellent and agree with measurements to very high degrees of accuracy, and are mathematically very simple and completely sound.

Originally posted by Arbitrageur
Yes that's the apparent effect we observe. It makes us weigh a little less at the equator than at the poles.

This is correct.

Also from the perspective of a physicist, there is no such thing as centrifugal force, which is why it's called a "fictitious force".

Not true. It's a perfectly good force. There is no meaningful distinction between forces and "fictitious" forces. This terminology is just an artifact of some people in the 1700s not understanding anything Newton said or did. Anything that causes a change in momentum (or more generally, blah blah blah Euler-Lagrange equations) is a force, the end.

Originally posted by ImaFungi
What is thought to be the mechanism of earths gravity? why/how do objects stay on earths surface? (you answer with the word gravity, but can you define what that word means or how it works, the most likely theory?

Originally posted by Arbitrageur
I wish I knew. That question is one of the reasons I studied physics, and I don't think I ever really found the answer I was looking for. Newton didn't really try to explain its origin, and Einstein's theory gives us more insights but I don't think the origin has really been fully explained, or if it has, someone besides me will have to answer.

This has been pretty well-understood since, uhh, the 60s or 70s at least? People already had the basic idea in the 40s or 50s.

From the low-energy point of view, gravity works the same way as any other force. The exchange of virtual particles. Just write down the Feynman diagrams describing the interaction of whatever particles you're interested in with gravity, the same way you do for QED or QCD or whatever.

This averages out, over large distances, to nice smooth Riemannian geometry. Why is well-understood, too. It has to do with the geometry of gauge theories, but is beyond the scope of a discussion on the conspiracy theory forums.

... an elusive topic called "quantum gravity".

If by "elusive" you mean well-understood, then yes... Again, the details of the various ways one can quantize gravity are beyond the scope of this discussion, but, despite what the internet claims, we know exactly how to quantize it and the answer is String Theory. We also know exactly why no other method works, or can work, even in principle.

What's not understood about it is a lot of the details--higher order corrections to cross-sections, details of behavior in various very short distance/very high energy regimes, the exact details of what constraints this puts on low-energy phenomenology, etc.