What causes gravity?

Chris OConnor · Posted: Sat Oct 16, 2004 8:59 pm Post subject: What causes gravity?

What causes gravity?

Tonight I was talking with my father about this question. My answer was that we really don't know what causes this phenomenon. We can describe or quantify the effects of gravity, but we don't have a clue as to how to define or explain gravity.

Gravity is simply something that happens when you have mass. All objects with mass attract other objects with mass.

But doesn't light get bent by gravity? Does light have mass? Anyone care to explain this further and without confusing everyone with formulas and lingo?

Chris

"Education is the most powerful weapon which you can use to change the world." - Nelson Mandella

Mr. Pessimistic · Posted: Sun Oct 17, 2004 9:06 am Post subject: Re: What causes gravity?

I do not know much about it, but I have heard that light indeed has mass. That is all I can offer at this time because, not to be redundant and repeat the same thing over and over and over...but as I said, I dont know much about it.

Mr. P.

The one thing of which I am positive is that there is much of which to be negative - Mr. P.

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HEY! Is that a ball in your court? - Mr. P

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Interbane · Posted: Sun Oct 17, 2004 3:27 pm Post subject: Re: What causes gravity?

Honestly, I have a theory that explains gravity and have been trying to contact anyone who can tell me if I'm full of @#$% or if there is a potential that I'm correct. I've emailed 13 different physics professors and have not heard a reply. I can explain the theory here, but it might take a while.

Also, I have not studied physics past the high school level. I've read many books by Stephen Hawking, Carl Sagan, Brian Greene and others, but I do not consider them as informative as a college education.

That said, I'm sure that my theory is incorrect... possibly for a pretty simple reason that I cannot see. BUT - how will I know if I never try.

booper54 · Posted: Sun Oct 17, 2004 4:54 pm Post subject: Re: What causes gravity?

FUCK I HATE MY COMPUTER! I typed out the whole message but it screwed up. Ugghhh....

Interbane: If you want to, explain it! I'd like to hear it.

mr. p: I'm pretty sure that light does NOT have mass. If it did, according to special relativity, it would have an infinite amount of it because of the equation E=mc^2....

Chris: I think this question is one that stumps a lot of the physicists trying to get rid of the paradox between general relativity and quantum theory. I remember reading about string theory and it explained gravity as a particle called a "graviton." But like mr. p, I don't really know much about it either.

Chris OConnor · Posted: Sun Oct 17, 2004 5:45 pm Post subject: Re: What causes gravity?

Interbane

I'd love to hear your theory. As long as you're humble and don't claim to know you're correct most open-minded people are pretty receptive to new ideas....I think and hope.

Chris

"Education is the most powerful weapon which you can use to change the world." - Nelson Mandella

Interbane · Posted: Sun Oct 17, 2004 5:52 pm Post subject: Re: What causes gravity?

I must ask a quick question first. Also, I don't have time to translate the whole theory from mind to language right now. That's an interesting way to put it, huh? My fingers thought of that one. Sorry, I went camping all weekend and feel like I'm on drugs, my mind is working wierd.

The question:

It is said that the faster you travel through space, the slower your speed through time becomes relative to a stationary observer. My question is if your spacial speed needs to be linear. Can it be rotational speed, or reciprocating speed(back and forth)? If so, there are only two other obvious questions to be asked before my theory passes my pre-release scrutiny.

Chris OConnor · Posted: Sun Oct 17, 2004 11:03 pm Post subject: Re: What causes gravity?

I would think that it refers to speed in relation to a light source, but what do I know. Seems like you are thinking about some sort of vibrational frequency.

Chris

"Education is the most powerful weapon which you can use to change the world." - Nelson Mandella

booper54 · Posted: Mon Oct 18, 2004 12:07 am Post subject: Re: What causes gravity?

Quote:
It is said that the faster you travel through space, the slower your speed through time becomes relative to a stationary observer. My question is if your spacial speed needs to be linear. Can it be rotational speed, or reciprocating speed(back and forth)? If so, there are only two other obvious questions to be asked before my theory passes my pre-release scrutiny.

Aaahhh! I just finished a relativity book and I know it explained this specifically, but I don't remember how. However I do remember the author (Einstein) used an example that a rod placed on the edge of a rotating circular plane would be shorter the faster it went with respect to a different reference system. I'm fairly certain that this is the same effect it has when it's moving in a straight line, which means the answer to your question is yes, it can be rotating speed in the same way it is linear speed.

Edited by: booper54 at: 10/18/04 1:25 am

Interbane · Posted: Mon Oct 18, 2004 9:30 am Post subject: Re: What causes gravity?

Ahh, good good. It's possible you're wrong, but let's pretend you're right. Next question.

Some scenarios are presented in theoretical physics that say after X amount of time moving very near the speed of light, person Y will be younger than his brother, person Z. This is because the faster you travel through space, the slower you travel through time. Kinda like a hypothetical velocity scale. More space speed, less time speed.

To keep that idea symmetrical, I've heard that we are traveling at the speed of light through time relative to someone who is right next to us, unmoving. So when you are sitting next to your wife, you are both moving at the speed of light 'through time,' since neither of you are traveling at all through space.

My question is this - to keep symmetry, should it not also work that if time were to slow way down, your spacial speed would need to increase to keep the balance, just as it is vice versa? This question is probably the most important one, and I cannot see an answer to it anywhere.

Let me explain to you my uneducated reasoning for thinking the answer is yes. Spacial speed consists of speed through 3 dimensions. If you are traveling straight through one of those dimensions and shift 90 degrees to travel straight down another, that takes energy. Believe it or not, that change of direction is also called acceleration, just as an increase in linear speed is acceleration. When you travel at a 45 degree angle to 2 of the dimensions, your true linear speed may be 50 miles an hour. If you measured your speed on the axis of one of those 2 dimensions that you are at an angle to, you might be traveling just 33 miles an hour down that dimension. Mathematically, your speed is somehow split between the two dimensions.

To envision my scenario with light, all you have to do is throw in the 4th dimension, time. The faster you travel through the time dimension, the slower you travel through one of the space dimensions - until you are standing still relative to your observer. Conversely, the slower you travel through the time dimension, the faster you must travel through one of the space dimensions to compensate. "If a pocket of space that is stationary relative to you suddenly experiences a slowness of time, you would start moving in a linear direction - most likely toward the pocket." - me

Edited by: Interbane at: 10/18/04 10:32 am

booper54 · Posted: Mon Oct 18, 2004 2:37 pm Post subject: Re: What causes gravity?

That's an interesting theory, but I think you are wrong. The reason time moves slower the faster you go (with respect to a reference system) is because of the Second Postulate of Special Relativity which states something like "Light in a vacuum moves at the same speed in all reference systems." So time moves slower only because it has to in order to keep all reference systems valid.

Chris OConnor · Posted: Mon Oct 18, 2004 3:10 pm Post subject: Re: What causes gravity?

Today there was an article on Space.com about gravity that might be of interest to participants in this thread discussion.

The Problem with Gravity: New Mission Would Probe Strange Puzzle
By Robert Roy Britt
Senior Science Writer
posted: 18 October 2004
06:33 am ET

Imagine the weight of a nagging suspicion that what held your world together, a constant and consistent presence you had come to understand and rely on, wasn't what it seemed. That's how scientists feel when they ponder gravity these days.

For more than three centuries, the basics of gravity were pretty well understood.

Newton described the force as depending on an object's mass. Though it extends infinitely, gravity weakens with distance (specifically, by the inverse square of the distance). Einstein built on these givens in developing his theory of relativity.

Then more than a decade ago a researcher noticed something funny about two Pioneer spacecraft that were streaming toward the edge of the solar system. They weren't where they should have been.

Something was holding the probes back, according to calculations of their paths, speed and how the gravity of all the objects in the solar system -- and even a tiny push provided by sunlight -- ought to act on them.

Now scientists have proposed a new mission to figure out what's up with gravity.

Staggering possibilities

Pioneer 10 and 11 launched in 1972 and 1973. Today each is several billion miles away, heading in opposite directions out of the solar system.

The discrepancy caused by the anomaly amounts to about 248,500 miles (400,000 kilometers), or roughly the distance between Earth and the Moon. That's how much farther the probes should have traveled in their 34 years, if our understanding of gravity is correct. (The distance figure is an oversimplification of the actual measurements, but more on that in a moment.)

Scientists are quick to suggest the Pioneer anomaly, as they call it, is probably caused by the space probes themselves, perhaps emitting heat or gas. But the possibilities have been tested and modeled and penciled out, and so far they don't add up.

Which leaves open staggering possibilities that would force wholesale reprinting of all physics books:

Invisible dark matter is tugging at the probes
Other dimensions create small forces we don't understand
Gravity works differently than we think
Devoted to the problem

Slava Turyshev at NASA's Jet Propulsion Laboratory is one of a handful of scientists who wrestle mentally with the Pioneer anomaly every day. He is not paid to work specifically on the problem, so he has to juggle the disturbing thought with his regular research, which involves other aspects of gravity and, significantly, whether theories that explain the glue of the whole universe might one day match neatly with those describing the invisible, subatomic world.

"I have been working on [the Pioneer anomaly] for more than 11 years now, and was never funded to do this job," Turyshev tells SPACE.com. "I guess this says a lot about my devotion to solve this mystery."

Data from the Galileo and Ulysses spacecraft suggest the anomaly may have affected them, too. But neither has been far enough from the Sun -- the dominant source of gravity in the solar system -- to firmly distinguish any possible discrepancy from noise in the data, Turyshev says. Galileo was crashed into Jupiter last year, and Ulysses will never go farther than it has.

That leaves two data points -- one from each Pioneer craft. Turyshev pointedly considers the pair as one data point, so as not to inflate the case for strange new physics. He looked at the two Voyager spacecraft, also exiting the solar system, but says their design involved "numerous attitude-control maneuvers" that "can overwhelm the signal of a small external acceleration."

NASA engineers have made their last communications with the Pioneer probes, so the two table-sized robots are carrying the unsolved mystery silently to the stars.

New mission proposed

The Pioneer anomaly was discovered by John Anderson, also of JPL, in the 1980s. For years he didn't publish what he'd noticed. Then he discussed it with physicist Michael Martin Nieto at the Los Alamos National Laboratory. Nieto says he "almost fell off my chair."

Nieto jumped into the investigation, and the two were later joined by Turyshev. They dug deeper into the data, even tracking down retired NASA scientists for some of it.

Unraveling the enigma will require a new mission, the researchers say. NASA, however, doesn't have such a project on its agenda and has not expressed much interest in one. Europeans, for reasons both historic and having to do with a current strong desire to better grasp gravity, seem more interested in investigating the problem.

So Anderson's team recently proposed to the European Space Agency a "mission to explore the Pioneer anomaly" using the latest accelerometers and advanced navigation methods. All possible sources of onboard radiation would be eliminated in "the most precisely tracked spacecraft ever to go into deep space," the group writes in the September issue of Physics World magazine.

The idea has "very high chances" of being chosen for future study, Turyshev thinks. If funded, it could launch as early as 2015.

If the mission were to find a natural, cosmic cause to the Pioneer anomaly, the revelation would rank right up there with other apple-on-the-head moments in the history of physics.

"If the anomaly is due to some new physical mechanism, this discovery would have a truly fundamental impact," Turyshev said.

Exotic candidates

One candidate is dark matter. This unknown stuff seems to infuse the universe and, though invisible, has a collective gravitational impact greater than all known matter, including stars and planets. Dark matter is inferred to exist because, without it, galaxies would fly apart. Every galaxy must be loaded with the stuff, astronomers conclude, based on how stars are bound to orbit the centers of the galaxies.

But dark matter's effects have been presumed to operate across large expanses, both within and between galaxies. There is no evidence of it controlling anything on a scale so small as our solar system.

Another idea is that gravity tugs slightly harder at things farther away. That radical suggestion, if proved true, would force a modification of Einstein's general theory of relativity and might eliminate dark matter as a player.

Yet one more exotic possibility: Dimensions exist beyond the four we know (three directions and time). Models of string theory propose that higher dimensions could provide weak forces that act in ways we don't yet comprehend.

No fancy theory in existence, however, properly explains the Pioneer data.

Drifting journeys

The Pioneer anomaly is not actually a measure of how far the Pioneer probes did or didn't travel.

Instead, scientists bounced microwave signals off each probe and noticed an unexpected drift in the Doppler frequency as the probes got farther away. The technique is akin to noting the sound change in a siren as an ambulance races first toward you, and then away from you. The Doppler effect is a shortening or lengthening of sound waves (or microwaves, or any waves) forced by an object's movement.

The drift showed that the Pioneers were being accelerated toward the Sun (or, rather, decelerated in their movement away from the Sun) by a tiny but inexplicable amount. The level of drift is equal to a gravitational effect 10 billion times weaker than the pull of Earth.

Though tiny, the signal is clear, other scientists agree.

Despite 11 years of devotion to the mystery, Turyshev is the first to admit that the "most obvious explanation" would be an unknown onboard effect. Perhaps excessive internal heat or leaks of propulsion gas are providing a wee bit of thrust that adds up over the years.

Yet despite a lot of testing, "no unambiguous, onboard systematic problem has been discovered," he said. "This inability to explain the anomalous acceleration of the Pioneer spacecraft with conventional physics has contributed to the growing discussion about its origin."

Even if the anomaly is caused by the Pioneer probes themselves, figuring it out will be useful says Turyshev, who is the proposal leader for the U.S. group.

"Finding it would help us to build a better spacecraft for the needs of fundamental physics," he said. "These craft would much more stable, quieter and would allow us to go even deeper in our quests of studying the fabric of fundamental and gravitational physics."

This article is part of SPACE.com's weekly Mystery Monday series.

"Education is the most powerful weapon which you can use to change the world." - Nelson Mandella

ZachSylvanus · Posted: Thu Dec 30, 2004 12:51 pm Post subject: Re: What causes gravity?

Electronegativity on the scale of larger objects such as planets etc. does not function as an attractive force, because the amount of contact able to be made electrically is too small to explain the attractive force observed. Plus, most bodies tend to be electrically neutral, which negates any sort of electromagnetic attraction between two objects.

Van der Waals forces (electromagnetic attraction between two surfaces in close proximity) are a weak force overall, and do not generally aid larger bodies.

ttalkman · Posted: Thu Feb 03, 2005 10:39 pm Post subject: Re: What causes gravity?

Since I was 4 years old, I have grappled with this very question. Ever since an early neighborhood friend pointed to his driveway and said it was "gravel". I thought my god, that must be what gravity is, rocks.

To this day, I have yet to figured out what gravity "is". I have always had the feeling though that it relates to negative charges found in atoms or other charges founded in sub atomic particles. They just act and look differently depending on what level they are acting upon.

It is troubling that it's root cause has not been found. It's overt behavior is so familar and so quantitized mathmatically yet so mysterious.

I have asked others what gravity is and their standard answer always is an "attractive force between two masses". They go on to describe the behavior. When I ask what causes mass to act that way, they end up just starring at me blankly or in bewilderment. They think it's a trick question because everyone surely knows what gravity is.

Some people are perplexed when they realize we really don't know what gravity is after all, only it's behavior. They somehow feel scientists already know.

Is it just me or has this question bugged other people all their lives too?

Interbane · Posted: Fri Feb 04, 2005 10:29 pm Post subject: Re: What causes gravity?

I thought electronegativity only worked on small scales?

Also, how does that differ from the Strong or Weak Nuclear forces?

Doc: "In some way, it is a bit ironic that we must try to be more stupid to obtain salvation."

MA: "I can't think of a better way to convince a group of critical thinkers of the worthlessness of faith."

rellimlk · Posted: Sun Apr 10, 2005 11:52 am Post subject: Re: What causes gravity?

I agree with Interbane that non-fiction books for the lumpen are no substitute for a PhD in physics. While I'm not the sort of person who has 8 years and $100,000 for the degree, I am the sort of person that has a couple weeks and the $2


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