What is Gravity?

Sir Newton will tell you that gravity is the attractive force that exists between any two masses. Prof. Einstein corrected (or expanded) that idea, and today gravity is defined by the concept of relativity. It is still the attractive force between two masses, but it is also so much more.....

Gravity is often one of the more annoying features of our universe and this is rarely more true than when trying to explain it.

At best I can only direct your friend to look into M theory, gravitons, branes, loop quantum gravity and so forth. It shouldn't take more than a decade to do this thouroughly, but I recommend frequent alternnating breaks for aspirin and the ethenol-bearing beverage of his choice.

My personal suspicion is that gravity is merely a construct to keep all the dust down.

Gravity is what makes what goes up come back down.

The force of gravity becomes greater as you add more material to the 'main' object.

Add enough material, and the combined density of the materials will create enough heat and pressure to burn in a nuclear fashion.

Add even MORE material... a LOT more... and the space between the nucleus and the really heavy, but infinitely small electrons will decrease to the point where even photons of light will not reflect.

....add even MORE! and you have a universe that collapses with such force that it explodes and starts all over again.

It's cool stuff..

...of course all of this is my own dumbed down speculation. . no facts were harmed in the generation of this response.

...so i guess you could say I'm so full of it that I should carry a fire extinguisher.

Gravity is an illusion. It does not exist. The phenomenon we call gravity happens because everything in the universe sucks.

Yeahhhh, right!

Gravity...? Then why have we not observed tides in our atmosphere? ...or any atmosphere?

Bobguz

Actually, there are tides in the atmosphere, but we don't notice them because we are at the bottom of this ocean of air.

Likewise, critters that live on the bottom of the sea don't notice those tides unless they are near a coastline.

You are correct for atmosphere.

But on the other hand there are tides for the ground (earth surface). We are on the earth surface. Still we do not feel the tide.

Pardon, but, unlike fish, we would perceive tides in the atmosphere as a diurnal change in barometric pressure. That don't happen. Also a tidal change in the altitude of our atmosphere would quickly slow anything in low (??) orbit. I never heard of that either.

Bobguz

"If we all worked on the assumption that what is accepted as true is really true, there would be little hope of advance." -- Orville Wright

You apparently have never observed the output of a graphing barometer! I'm not at home right now, so I don't have any available to post, but when I get home in a couple of days I'll see if I can do that.

There IS a diurnal change in barometric pressure, and just like in the oceans, one of the highs is regularly higher than the other. The tides in the atmosphere tend to be masked by changes due to weather, but it does not take a meteorologist, just a careful observer, to see them.

All satellites have to be high enough to be above virtually all of the atmosphere, or they would (and eventually will, unless they are periodically boosted back up) be slowed by the atmosphere, tide or not.

Dick

Lets consider the gravitational attraction between a pretty girl and a boy.

If a 50 kg (110 lb) pretty girl sat 0.5 m (19.7 in) from a boy who was 75 kg (165 lb), what would be the gravitational attraction between them?

According to the Universal gravity equation we get:

F = GMm/R² = (6.67*10^-11 N-m²/kg²)(50 kg)(75 kg)/(0.5 m)(0.5 m) = 10^-6 N or one-millionth of a Newton

That is a very small gravitational attraction, but it can be measured on a sensitive instrument.

At least, thats what I would tell the girl.

Most engineers That are not in electronics at Component level are quite content to live in Newtons Universe.

Example calculation frm http://www.school-for-champions.com/science/gravity_universal_equation.htm where you should send your friend.

milo

But if girl is sitting on the laps of the boy, R becomes very small. Please let us know what will be the gravitational force.

Also if girl is of 75 Kg and a boy 50 kg. what are the effects in above case?

In the case of a 75 kg girl and 50 kg boy, the math formulas give the same answer, but the "sensitive instrument" usually fails to respond to any attraction.

milo

So you want to say a 500kg girl will be more attractive?

The numbers say that. I have a somewhat different answer...

milo

Science has yet found out how it works. But no body has yet understood why it is so.

So no answer to your question "Where does that....."

Ask Jorrie, he is the CE4 expert on the subject of relativity.

Get an ebook copy of "Relativity 4 Engineers."

Good post, Vermin! There is still a debate going on re "gravity waves" and Gravitons.

If a Graviton is essentially massless, like a photon, and if even photons can't escape from a massive body, such as a black hole, why do we think that black holes radiate gravitons? If matter (atoms) in a neutron star are basically collapsed atoms where the electrons and protons have been crushed together to produce neutrons, then what form of matter exists in a black hole (Singularity?) Because the black hole does have "gravity", matter / mass must still exist in the black hole.

This is where Relativity and Quantum Physics get in a fight and don't speak to each other for several days.

QM has been able to explain all the forces by the exchange of virtual particles... Except one - they just can't seem to find that "Damn elusive Graviton!"

Great post. Consise, percise, and to the point.

Thank you,

Orpheuse

You asked:

"What is gravity?" : It's the attractive force between masses or energies due to the curvature of the "space-time continuity" which is caused by the presence of these masses or energies (according to the General Relativity of Einstein)

"Where does that pulling force come from?" It comes from masses or energies (as I've already told you)

"What is it's purpose?" : What is the purpose of everything else???... Its existence is not more mysterious than the existence of everything else...

"Actually why it pulls & not repells?" : I could ask: why electric or magnetic force pulls or repells and doesn't, always, pull??? ... It's just the nature of the gravity as there are not positive and negative masses in order to have, correspondingly, attraction or repulsion (due to gravity)... It's not like i.e. electric force which is caused by positive or negative charges...

Although it is important to note that anti-matter acts the same way a regular matter in a gravitational field.

I understood Gravity in my own way.

There is always some analogy between the basic element & something that is made of that basic element.

E.g. Atom - It has a nucleus & electrons revolve around it.

Solar system – Sun is the center & all the planets revolve around it.

Milky way – Whole solar system revolves around its center.

Earth – Earth is the center & moon revolves around it.

It's the same pulling force that nucleus of atom exerts on electrons & it goes on increasing as the size of matter (of course, which consists of atoms) increases. Even we (human beings) are having our pulling force (there are some psychics who can actually use it and move objects without touching).

Am I going the right way?

Gravity is such a weak force with respect to other forces (i.e. electric forces)...

Even though the nucleus of the atom applies, theoretically, some gravitational force to the electrons around it, practically, this force is veeery close to zero... Practically, only the electric forces keep electrons close to the nucleus...

Gravity is sooooo weak that you need really big masses (like planets or galaxies) in order to be observed in a fairly large distance...

Planets are not attracted to each other due to i.e. electric forces as they have almost egual quantity of positive and negative charges (thus cancelation)... Although gravity is sooo weak it succeed to mutualy attracts planets because it can never been canceled and always is increased if more mass is added... So, when we have huge masses (or energies) the effect of gravity becomes significant...

(By the way another person standing close to you applies to you a gravitational force much bigger than the gravitational force which is applied to you by the moon... But in both cases, practically, you don't sense anything...)

You need to understand gravity of the gravity

You may be right about people having a "pulling force". For every force there must be an equal but opposite force. And I can prove it, for I have mastered anti-gravity!

I've tried...I mean REALLY tried...to focus my pulling force to attract pretty young girls into close orbit around me. And after decades of trying I have discovered that I can easily repel them to great distances away. Clearly all I have to do now is figure out how to reverse my polarity.

All you need to do my boy is to flash money at the sluts- they'll do anything for it- but never marry one- they'll take you for everything you've got(had!).

ah, lower your expectations?

"...there are some psychics who can actually use it and move objects without touching..."

You ask if you are 'going the right way'...not if you actually believe the above statement quoted from your post. There are NO psychics, only those who claim to be. Nobody can move objects without touching them in some way. I can blow on a sheet of paper and make it fly across a tabletop, but I am touching it with the air I huff at it. Please do not fall into the trap of believing there are people who can do everything they claim to do. Most of them are skilled illusionists, and the rest are just plain fakes.

NO!

I still hold with the idea that gravity, although a fundamental force, is really a problem with massive bodies interfering with the space-time continuum.

If the space-time continuum is imagined as a pliant flat surface, like a huge rubber floor, a planet makes a dimple in space -time into which matter tends to aggregate. That makes space-time the effect and gravity then becomes a matter (no pun intended) of perception. I.E. Things fall into a gravity well because space-time is warped by all the dimples.

Now are we looking at a force and wondering if it is really the effect of a process, rather than a force. Albert hated this, Hawking loved it. Go figure.

Ari

Orpheuse

What's your point? All forces are the effect of processes. The interesting thing is why does matter bend space-time? And it does not "interfere" with the continuum -- that's way to subjective. It's just an aspect of the continuum.

On the other hand, there is a physicist that has questioned the concept of a "continuum." This new model implies that far from a continuum, space-time is more like a fabric with many individual threads.

Hi, Vermin,

I am wrestling with the thought that "all Forces are processes". I understood that the 4 forces were intrinsic to the Universe. The Universe, as we know it, is dependent on the forces and the forces are dependent on the universe. One cannot exist without the other. One thing that appears to be true is that matter seems to attract light to the itself. That the more matter, the more material-attraction.

"On the other hand, there is a physicist that has questioned the concept of a "continuum." This new model implies that far from a continuum, space-time is more like a fabric with many individual threads."

What's the difference between that and "the rubber floor"?

Are you referring to "String" and Super String" theory? And while we are on the subject can you define "continuum". I know what I mean but I'm ain't sure what you mean.

Thanks V.

Ari (Orpheuse)

I said threads, not strings.

Yes, although the term "continuum" gets thrown around a lot to mean many things (like the Universe, for example), it does have an actual definition. The continuum refers to the concept that all of the space in the Universe is one, single, continuous thing. Unlike the rubber sheet, if you go down far enough, you find it made of molecules and atoms...

In the concept of the continuum, there is no substructure. And Yes, the very concept of the continuum is under attack from a number of directions, and may someday be an archaic term.

"This new model implies that far from a continuum, space-time is more like a fabric with many individual threads."

Are these threads 1 Planck-length apart?

This sounds like a thread theory competing with my own. Mine is to replace string theory and doesn't have a thread of truth in it. HeHe, just kidding.

S

I'm tired of your whining! Please put Eurydice on the phone.

While this is a good statement of what we know, the problem is that it is just a description of what it observed, not an explanation. The analogy of the dimpled rubber sheet with matter accumulating in the dimples only helps us visualize what it happening. The analogy depends on the still unexplained force of gravity, working perpendicular to the plane of the rubber floor, to 'pull' the matter 'down' into these dimples. So it is an elaborate visual representation that in the end relies on our conventional view of gravity as a downward force to make its point.

We still have no idea whether the space-time becomes warped in response to the presence of matter (or mass), or whether it is the warping of space-time that initiates the clumping of matter, or whether the presence of matter in the warped areas of space-time is a response to some other and as yet unknown force. We don't know if matter is in fact merely a property energy, or of space-time itself, that appears where there is an intense quantum-scale warping of space time. What we should consider is that there is some very important piece of the puzzle that is missing, or that we are trying to include a puzzle piece that just doesn't fit.

"The analogy depends on the still unexplained force of gravity, working perpendicular to the plane of the rubber floor, to 'pull' the matter 'down' into these dimples. So it is an elaborate visual representation that in the end relies on our conventional view of gravity as a downward force to make its point."

I agree. The analogy doesn't do much for me. I like to ask people what is the source of that perpendicular gravity - "a giant turtle, perhaps?"

First, the rubber sheet thing is just a 2-D representation of a 4-D phenomenon. Space is warped in 3 dimensions (not 2) and time is also altered by the same process.

Second, MATTER WARPS SPACE/TIME. Take a heavy object into space. Where that object resides, there is a gravitational field. Now, move the object to a different location... Guess what! The gravitational field is now there. If you go back to the object's original position, the gravitational field at that place is gone!

It's maaaagic!

According to Dr. Einstein, the three dimensions of space and the dimension of time are connected. A massive body like the earth bends this space-time. As you travel through time, if you are in free-fall, you follow the curved lines of space time. If you are constrained from falling (sitting in a chair, for example), you are being constantly accelerated, which you feel as a force, just like the force felt in an accelerating automobile.

Gravity is seriousness...as in, tending towards the grave...that pulling downward, into the ground, force that your friend was concerned about. Give him another glass of wine and tell him no one knows and, ultimately, no one cares.

The earth is spinning. Centrifugal force is trying to sling you into space. Gravity keeps it from happening. What more do you need to know?

No one really knows that it only pulls. That it doesn't actually push. After all, when you "feel gravity" you only sense weight, not bring pulled, any more than being pushed. In fact, from the perceptual point of view, pushing might better explain the thing we call gravity, for lack of any better word.

(PS. My wife made me a bet about this post...)

UG

Try jumping out of an airplane a mile or 2 up. You'll feel the pull.

Hmm. Felt more like the push of the wind.

What was the bet?

Ari (orpheuse)

Gravity always pulls.

Time also always pulls.

Probably for the same reason.

Someday we'll understand.

Then time travel will be possible.

Is this poetry?

I have heard it explained that according to general relativity, the decay of orbits over time is taken as proof that gravity (gravity waves of gravitons - both as yet undetected) must travel at the speed of light. I'm not yet convinced. I think that it is worth considering the possibility that gravity simply is - it does not travel -that it exists outside of time. Probably impossible to prove, since experimentally it would seem to require the almost instantaneous creation of destruction of matter to demonstrate.

Of course this is bald faced speculation, but then attributing gravity to undetected waves and particles is much the same thing. There has been quite a lot of time an effort spent looking for gravity waves, with no success as yet. Maybe we just need better experiments and equipment. Maybe we're looking for something that isn't there.

On the other hand I understand that there are experimental setups using 'circulating light' from carefully aimed lasers that appear to be able to at least slow time down. If this is the case your hypothesis may be more testable.

Hi John,

"I understand that there are experimental setups using 'circulating light' from carefully aimed lasers that appear to be able to at least slow time down."

Sounds interesting. Do you have any references?

regards,

S

Well the reference is pretty vague. This was part of a documentary on the Science channel on The Time Paradox. It featured Dr. Ronald L. Mallet, an astrophysicist, who had lost his dad at a young age and become fascinated with the idea of time travel. Fearing ostracism as a whack job for choosing this field of study, he studied black holes.

In the experiment in question he arranged four stacks of lasers positioned at 90 degree angles aimed into a cavity. They were positioned such that each stack of beams was aimed just to the left of center, so that it created a clockwise 'eddy'. It sounds far fetched, but the circulating curtains of light actually produced a rotating magnetic field, which according to his theory would, if strong enough, slow down time in the center of the cavity. I don't honestly remember that he claimed that in his rig that he was slowing time or how he proposed to demonstrate that he had - only that he had created the right conditions.

Sorry that this source is pretty weak. Here is a link to a youtube page that has some videos from the documentary, and some other sources.

http://www.youtube.com/watch?v=NS1-SZ2L81k&feature=related

It's close. But I got the feeling that time actually pushes. I know the older I get, the more I feel pushed into the future, rather than being pulled along by it. Perhaps my perceptions are skewed. How about this:

Gravity appears to pull.

Time however, pushes.

We may never know the reason.

If someday we understand,

We'll know if time travel's possible.

In reply to 42.

Definitely poetry.

I discovered that the chances of winding up on a flight with a bomb onboard is a billion to one. While unlikely, I prefer better odds. So, when I found out that my odds of boarding a flight with two bombs onboard was a trillion to one... Heck, I'm no fool! Now every time I fly, I carry a bomb with me!

Hi pc,

What is gravity? Many cosmologists would like to know. It's the opposite of that unknown force that is expanding our universe (assuming it is expanding - the jury is still out on that.) Send your friend to the library, to the children's section, and he can work his way up from there.

S

p.s. The force between a boy and a girl is electricity. It repels until puberty, and then starts to attract. After 50 it begins to repel again, depending on the woman's weight.

It has nothing to do with weight. It has to do with knowing someone too well

Orpheuse

"Most people are pretty sure that gravity exists, a smaller number is pretty sure what it does ...but nobody is at all sure of 'how' it works."

Gravity is produced by supermassive particles (as yet undetected) which flood our universe, moving in every direction. Most of them pass through our planet producing no effect. A fraction of them collide with the atoms in the earth, transferring momentum and creating a net inward force. When I stand on the ground the earth partially shields me from the particles that come from the "down" direction. This creates a net downward force on my body, produced by the particles that are coming from the "up" direction. When two bodies of similar mass come into proximity (such as two stars) each partially shields the other from the particles, creating a net force on the bodies which pushes them together.

Bill Morrow, Cosmology Heretic

To bmorrow:

I like!

Thank you, thank you. You're a wonderful audience.

Bill Morrow, C.H.

P.S., C'mon somebody, give me another "good answer". Pleeease!

Where the heck did you get that story from - I get better science advice from...

You're talking pure, weapons-grad balognium!!!

Vermie old pal,

I got my gravity explanation directly from Dr. Fry himself. I think he got it from Zoidburg.

Well, what the hay, at least I offered an explanation. Still, I simply threw it out as an (hopefully) interesting idea. The Newtonian formula is actually only a description of what is observed, not an explanation. While relativity seems to accurately describe what is observed, it is, so far, still a theory (yes, one that has held up exceedingly well).

That's my two cents worth. Perhaps I owe you some change.

Bill Morrow, Cosmology Heretic

Don't look at me. I'm still trying to break back into TV!

Interesting idea. I haven't yet taken the time to think this through so I'm probably missing something obvious, but I have a concern that this would not produce a gravitational gradient that conformed to the inverse square law. Do you have a diagram that would explain how this works out?

I think it would be more interesting to ponder Mag's idea that gravity is inertia in time. Hmmm?

Sorry John. What I said is all I have. Just some idle musing.

Bill Morrow, Cosmology Heretic

Bummer. I'll try to model it and see if it would follow the inverse square pattern. It's such a novel idea.

OK.. back to the atomic level.. and really simple..

There is a small electrical charge in all matter that holds it together like static...

Electrons really want to orbit their own nucleus in a very electrical way.

The same 'magnetic' force draws atom together in bunches, but the force is still rather weak.

The more of these atoms sharing space together, the stronger the 'static cling' (didn't i just say magnetic?)

The only thing that keeps us from falling to the ground at a greater speed speed is the thick goo of atoms that don't stick to each other very well that we call atmospheric gases.

If you were able to land on one of our larger planets, you would find it to be quite featureless due to the fact that the massive amount of static/magnetic/gravity created by that HUGE bunch of atom's is enormous enough to crush topographical features. (and you)

It also why so many small moons and planets have HUGE natural features..

....SO.. even small things in space like the ISS have a certain amount of surface gravity, but not enough to 'matter' yuk yuk.

Sooo? Is it true? That even in a room full of 'eingineers'...? People must used shtick or talk about sex to get a pulse?

-now I know why people turn to the lord!

gravitate on this,,!,

There is no reason to assume that the universe is flat. It is, most likely, curved, and probably 'bumpy'. Gravity is the effect of a dip in space-time. The bigger the dip, the higher the gravity. Matter accumulates in the dips for the same reason that lint accumulates in your naval.

Orpheuse

speaking of which, don't forget to clean your lint screen./ab

"Matter accumulates in the dips for the same reason that lint accumulates in your naval."

Because we pour in Ketchup and dip our French fries in there?

Ketchup (catsup?) IS gravity!!!

Dr zarkov thinks that gravity is a push not a pull- could be true- eg in a wind powered device the wind push is stronger- but all depends on the relative mass of interacting masses- take the earth- the sol outputs massive energy wind- in all directions- the recipients are moving in an inertial manner- but the energy from the sol is a PUSH!. The energy from the recipients is negative- so the input is positive!. However, the mass of the recipient resists this inflow- so gravity is negative energy!.

Riddle me this.

How can there be "negative" energy...unless there is no positive energy?

Take all the time (no pun) you need.

Time is what is measured by the clock- nothing more(nor less) - Mr Einstein. IF earth eg is negative energy, then all forms of positive energy, such as life, must spend energy overcoming the push from MORE MASSIVE POSITIVE SOURCES such as mr sol, pushing down in an effort to reach equilibrium with negative energy- put another way, we are only able to resist in our own small way- when our positive energy fails, we revert to negative energy- mr sol then pushes us down without hindrance- death.

Where the heck did you get that... aaah stuff?!