quote:Originally posted by T_Smith: Yes, I know x's would be changed as well, since if it were on a steady pace, then it would take longer, due to y's change, to get to the next x coordinate. If that made sense.
That made sense, but it's not why x's rate would change. x,y,z,and t (and presumably other dimensions which probably exist) are all affected by the introduction of the gravity field. To an observer outside the gravitational field, one foot gets shorter and one second gets longer (if I have these right... I may be wrong about either one of them but they both definitely change) on your hypothetical earth in the new gravitational field.
Edit: as to why, it's kinda related to what someone else said about nothing being simultaneous.
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*digs deep in brain* (I've had AP Physics plus some college level self-study, and that was a while ago, so I'm not necessarily the best person on this forum to ask for verification ).
In a sense the question is meaningless without an observer (though since gravity is indistinguishable from acceleration the frame is no longer inertial). If (as T seems to suggest) the gravitational field is perpendicular to the movement of the earth (and the earth's own gravitational field is taken as negligible), then there are several effects going on:
Any relative movement by the earth has already resulted in the earth's dimension in the direction of movement being distorted. Movement towards the gravitational source will have similar effects in that direction. Time will appear to go slower.
If the observer is coplanar with the earth relative to the gravitational source, then no change due to gravitation is observed. If he is closer, then their will be some gravitational effect making time on earth appear to go quicker to the observer, possibly counteracting the effect of speed differences.
If he is further, then there will be some gravitational effect making time on earth appear to go even slower to the observer.
*crosses fingers* I think that's correct.
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"one foot gets shorter and one second gets longer (if I have these right... I may be wrong about either one of them but they both definitely change) on your hypothetical earth in the new gravitational field."
Now, do you mean this in a way of "the earth is still traveled a foot, it only seemed shorter because it was moving along a different plane?
If so, then lets say the gravitational field moved the earth away from the person who was viewing it. At that point, it would appear that a second was longer, since it took longer for the light to reach the observer. But if it moved closer, it would appear that the second was shorter since it didn't take as long for the light to arrive.
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Well, I read him to mean some hypothetical device is generating a localized gravitational field which affects the earth but not other things in the relatively nearby area...
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There is no seems, and no appears. These changes are. They are physical and real. However, they are also often contradictory. Fun, huh?
A foot for the earth got shorter. It really did. The people on earth would disagree, but that doesn't mean it didn't from your perspective.
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What I meant was the people on earth still see it as travelling a foot, but the person who observed it saw it as, say, half a foot.
What I was asking about is if the people on earth saw it as a foot because instead of only x changing, now y is changing as well? And that the person observing saw it as half a foot, because from their perspective, the earth is still only traveling on x?
Or did a foot just really change?
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I'm more familiar with doing this by motion, rather than by gravity well, but I know the gravitational effects are similar, so I'm going with that. I'm saying this as an addendum to the caveat that my last Modern Physics course was in the early 90's.
That having been said, you are correctly accounting for the effects of the earth starting to move in the y-axis because of the gravitational field.
*but*
There are other, similar, effects that occur merely from the earth's position in the gravity well... not from it's motion at all. as Fugu points out, though, it's not affecting all axes... that was my mistake, it only affects the axis in which the field pulls, in your example, I believe, the "y" axis.
And I do not mean "the earth still traveled a foot but it only seemed shorter because it was in a different plane. I meant that one foot on your hypothetical earth was actually shorter than one foot elsewhere. That a foot long hot dog on your earth, would measure less than one foot to someone away from it and observing from a (supposedly) non-inertial frame, though it would still be a foot long and measure one foot to someone on your earth. The actual, abstract length of "one foot" gets shorter.
Perhaps the best way I can put it is, a clock one foot tall in Death Valley is shorter and runs slower than an identical clock at the top of Mount Everest. *If* I don't have the equations upsde down because I only ever messed with moving objects, not gravity wells. I should add, though, it will still seem the same when viewed from nearby (i.e if you just pcik up the clock and move it, you won't see the difference because you are moving with it). It's only when comparing the two to each other that the differences become visible... to someone on Everest, the Death Valley clock looks to run slower and be shorter. To someone in Death Valley, the Everest clock looks to run faster and be taller, but if the person from Death Valley goes to Mount Everest, the clock will seem one foot tall and run "correctly".
Edit: apologies for using "seem". Fugu correctly points out that these changes are real... I was trying to emphasize that they are only measurable from other frames of reference. Tricky stuff... imprecise wording (a problem of mine) can get you all kinds of twisted in Modern Physics.
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Yep, the more relative gravity (like the more acceleration), the slower a clock is to an observer, and vice-versa.
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So lets say we have a clock at the bottom of Mt. Everest and one at the top. Both clocks running at the same rate. With both clocks seperated, the guy on the bottom and the guy on the top see their respective clocks hit Noon at the same moment. The guy on the bottom looks up at sees the clock at Noon, the guy on the top looks down and sees the clock at noon.
With that in mind, you're saying that after an hour passes, the clock on the top is going to be ahead of the clock on the bottom?
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Well, they aren't running at the same rate, but we can say they're both considering the same number of oscillations of the spectral emissions of cesium atoms to be a second.
If they happen to both appear to show noon to someone down in death valley, then a bit later he'll look up and the one on everest will be ahead, yes. Very minutely, of course.
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yeah, we're talking this effect wasn't measurable until the advent of the atomic clock, but they actually did an experiment with two of them and sure enough, Einstein was dead right on that one (though I gather Relativity is starting to show holes itself, now?)
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Well, holes at the level of the sufficiently small, but its had those a long time. And people keep going back and forth over the cosmological constant (existence and possible interpretations).
Yeah, there was a cool experiment with airplanes.
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What I meant by same rate is that if they were brought back at the same level, then both would be running a rate of 1s/s, regardless of what time each was showing.
The question I have, then, is why? And if there is no why, then fine. If we accept that as true, it means that the more gravity, the longer you live. Right?
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There is a why, its because light always travels at the same speed for all observers and inertial frames of reference are indistinguishable. For why this is the why for gravitational differences, you'll have to have more math .
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fugu, Or notice that Faraday's Equations of Electro-Magnetism are referentially agnostic, therefore whether you are standing still, or going 1 million miles per hour, doing EM experiments will yield the same result.
EDIT: Of course the reason the results are the same is because c (the speed of light in a vacuum) is c is c is c.
quote:Originally posted by fugu13: Well, holes at the level of the sufficiently small, but its had those a long time. And people keep going back and forth over the cosmological constant (existence and possible interpretations).
I suspect there may be other effects involved, but even if not I could see relativity being fairly easily reconciled with certain sorts of differences.
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I am having trouble comprehending what exactly is causing gravitational forces.
I comprehend that gravity is the tendency for two objects to accelerate towards each other.
I understand the inverse square law.
I understand that 2 objects in freefall, or inertial motion, are not accellerating with respect to each other.
What I do not understand is what is causing the attraction. There is nothing in between them, there are no invisible strings pulling them together. I do not accept that forces are the end all "there is no explanation, they just are" answer. I can't wrap my head around how a curvature of spacetime is going to cause gravity, if gravity itself is causing the curvature of spacetime.
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quote:Originally posted by T_Smith: I am having trouble comprehending what exactly is causing gravitational forces.
You are in good company.
The best demo I have seen to illustrate the theory of gravity warping space can be done at home. Take a sheet and stretch it tight (four people at the corners is the best way). Now place a bowling ball in the middle. See how the cloth dips towards it? If you now place a baseball near the edge of the sheet, it will most likely roll toward the bowling ball, (unless it is far enough away) because of the curvature of the sheet.
The theory is that mass somehow deforms the space around it in a 3-D manner similar to the 2-D effect of the bowling ball on the sheet.
Or there's string theory . . . Posts: 32919 | Registered: Mar 2003
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quote: I can't wrap my head around how a curvature of spacetime is going to cause gravity, if gravity itself is causing the curvature of spacetime.
Here's your problem. Gravity is not causing the curvature; gravity is the curvature. Personally, though, I find it very difficult to think of causality in this connection. I prefer to treat relativity as a highly accurate empirical model, something we use when we want answers on a large scale, and consider the causality as arising from the microlevel. (This may be a training bias, of course, as I am a particle physicist and not an astrophysicist. Perhaps if I'd gone the other way, I'd be happier with GR and consider it very difficult to think of what's 'causing' quantum mechanics to work.)
We usually consider forces as being caused by the exchange of messenger particles; in the case of gravity, it's called the graviton, and has not yet been observed, nor is it likely to be; gravity is so weak that stopping a mere neutrino is child's play by comparison. We know something about what properties it must have, though, just from looking at the large-scale behaviour. But I digress. Basically, all particles are constantly spitting out and re-absorbing force-carrying bosons. If you are visualising this as the bosons going out from the main particle, and then turning back, that's accurate but highly wrong. These are wave functions; essentially the carriers exist everywhere, and can be reabsorbed at will. Or you can consider them as not 'really' existing until they actually get absorbed by a different particle. Matter of taste.
Anyway, it's easy to see how this causes a repulsive force : Basically, you just throw a boson from one particle to another, and they'll repulse, right? Just like children on skates throwing snowballs at each other. (Who may also be repulsive for other reasons, but never mind.) What's harder to see is how this causes an attractive force; you almost have to visualise the bosons curving around like a boomerang to come at the target particle from the other end; and then what's causing them to curve? Fortunately, QM to the rescue again; the bosons are wave functions, and have a finite probability of existing everywhere in the universe. They can be going in direction X, and suddenly find themselves captured by a particle way off at minus X; but their momentum is still pointing at X, so the target particle gets a good kick in the direction towards the emitting particle.
Of course, this description is completely agnostic with respect to what kind of force you've got, so it works as well for gravity as for anything else. You just rarely see particle physicists talk about gravity because it's so weak, so unless they're wearing their cosmologist hats, examples usually use electromagnetism.
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"The best demo I have seen to illustrate the theory of gravity warping space can be done at home. Take a sheet and stretch it tight (four people at the corners is the best way). Now place a bowling ball in the middle. See how the cloth dips towards it? If you now place a baseball near the edge of the sheet, it will most likely roll toward the bowling ball, (unless it is far enough away) because of the curvature of the sheet."
The problem I have with this, is that I begin to wonder what the blanket represents, since there isn't exactly anything for say, the moon to be rolling on. Just emptiness. I begin to see the blanket as physical plane, and the ball is rolling downwards because the plane itself is now tilted. I can imagine a theoritcal invisible plane, but my brain says "oh hey, its space, there isn't anything physical there" and I go crosseyed back to my original question.
I get what you are pointing out, though. I understand the concept, just the practicality of applying it to the earth and moon isn't working for me.
King of Men- bosons? You'll find I have the need to repeat the already stated a lot when learning.
Ok- so we have particles, that I am, for the most part, are taking down the level of an individual atom. When you say boson, is that the previously mentioned messenger particle? Ok, so we have particles, spitting out and reabsorbing waves called bosons. Is a boson a wave or a particle?
So we have a particle that sends out a boson, say particle exists and 0, and particle boson is headed to is at 10. Boson gets to 5 and gets called back to particle at 0, particle at 10 then gets pulled in the direction of the particle at 0.
This then means that the more mass an object has, the more bosons it is emitting, and the more attraction it puts out.
Did I understand this, or did I totally flub this?
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quote:Originally posted by T_Smith: "The best demo I have seen to illustrate the theory of gravity warping space can be done at home. Take a sheet and stretch it tight (four people at the corners is the best way). Now place a bowling ball in the middle. See how the cloth dips towards it? If you now place a baseball near the edge of the sheet, it will most likely roll toward the bowling ball, (unless it is far enough away) because of the curvature of the sheet."
The problem I have with this, is that I begin to wonder what the blanket represents, since there isn't exactly anything for say, the moon to be rolling on. Just emptiness. I begin to see the blanket as physical plane, and the ball is rolling downwards because the plane itself is now tilted. I can imagine a theoritcal invisible plane, but my brain says "oh hey, its space, there isn't anything physical there" and I go crosseyed back to my original question.
I get what you are pointing out, though. I understand the concept, just the practicality of applying it to the earth and moon isn't working for me.
King of Men- bosons? You'll find I have the need to repeat the already stated a lot when learning.
Ok- so we have particles, that I am, for the most part, are taking down the level of an individual atom. When you say boson, is that the previously mentioned messenger particle? Ok, so we have particles, spitting out and reabsorbing waves called bosons. Is a boson a wave or a particle?
So we have a particle that sends out a boson, say particle exists and 0, and particle boson is headed to is at 10. Boson gets to 5 and gets called back to particle at 0, particle at 10 then gets pulled in the direction of the particle at 0.
This then means that the more mass an object has, the more bosons it is emitting, and the more attraction it puts out.
Did I understand this, or did I totally flub this?
Woo! Mathematics to the rescue!
Suppose you have a penny and it's forced to stay on the surface of a basketball. Pick your favorite two spots on the basketball (for ease, don't let them be on opposite sides of the basketball). Suppose you want to pick the "shortest" distance between those two points, subject to the fact that the penny must stay on the basketball.
We're used to saying "the shortest distance between two points is a straight line". However, this really only works on flat things. To convince yourself of this, draw two dots on a piece of paper, draw the straight line between them. Now, bend the paper. You line bends!
While this isn't proof, it illustrates a point - on curved surfaces, the shortest distances between two lines is NOT a straight line, but rather a curve.
So, Mathematically, how do we determine if something is "straight"? For some decent reasons, the official mathematical definition of a "straight" line is one who's acceleration is 0. Note that this totally agrees with what you're used to in flat space.
What this means for curved things, however, is that you allow some "force" to stick the object to the curved space. But in the same way you don't feel a "force" keeping you in the universe, sticking an object to the curved space doesn't require a "force", it's something more natural in the geometry of the shape.
Here's where Einstein comes in. He says, what if what the universe REALLY is is a bunch of space-time everywhere/when, which is naturally flat. Further, suppose mass (and therefore energy) can force this spacetime to curve. What happens to straight lines? Well, they curve now.
We earlier said that that the shortest distance between two points is a line (and showed how this really doesn't capture the whole truth). There's another fact flowing around. An object, in the absences of forces, takes the shortest distance between 2 points.
Put these together, and what path do objects take when there's mass/energy around? A curved one. Einstein called this effect "gravity".
Hope this helps.
Incidentally, some people have been saying that the effects due to gravity and the effects to do velocity are the same. They work similarly, but they are NOT the same. The velocity effect is based solely on SPECIAL relativity, a much easier theory where you can (almost?) solve everything algebraically.
When we start talking about gravity, we're inherently talking about GENERAL relativity, a MUCH more complicated theory. You can solve ALMOST NOTHING algebriacally (it's all differential equations and something called tensor equations). What this means is the gravitational effects on position/time are in the same vein, but very different.
Finally, one more caveat.
Earlier in the post, you guys were talking about choosing coordinates (x,y,z,t). I want to stress that you can ALWAYS do this locally (meaning close to you), but they won't be globally defined. In otherwords, there will almost always be regions where your previous definitions of (x,y,z,t) will just break down, due to the curvature.
This is because general relativity involves things called "manifolds". These are math things with a few important properties. Up close, they look flat (and flat things are the only place you can put (x,y,z,t) on). But far away, who knows what shape they are? If from far away, they are INCREDIBLY well behaved, then your (x,y,z,t) will work everywhere. But if, for instance, if you manifold is a sphere such a thing won't work.
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Also, remember that in essence, eferything at the subatomic level has wave-particle duality, That is, nothing is either one or the other, it just depends on the context.
KoM, the photon is the "carrier" boson (?) of EM, right? What are the matching entities for the Weak and Strong forces?
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Weak force has W and Z bosons, and the strong force has gluons. I'm runninglate for work or I'd put a bit more work into re-explaining the force carrier thing.
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Like Einsteins gold sheet thingy, right? Or was that some other dude? Do particles with wave-particle duality travel in a straight line, or do they follow the wave itself, going from crest to trough?
I've gone and tried to attempt to show how my brain is now configuring how space time is curved. I decided to draw a circle representing a gravitational source, and then drew another circle comprised of different colors, where it is a spectrum from red to violet, violet representing faster rate of time, red representing a slower rate of time. Taking inverse square law into the equation, I showed how the rate of time changes correspondingly, to show that based upon location to a gravitational source, the rate of time changes.
Like Einsteins gold sheet thingy, right? Or was that some other dude? Do particles with wave-particle duality travel in a straight line, or do they follow the wave itself, going from crest to trough?
I don't think it was Einstein. Your third sentence shows the misconception. There is no particle, only the entity that has wave-particle duality. Based on the qualities that a subatomic entity can have, they will behave more like what we consider as a wave (or particle), but in reality, they are both (or rather neither, they are an entity that we descibe as having these attributes).
quote: I've gone and tried to attempt to show how my brain is now configuring how space time is curved. I decided to draw a circle representing a gravitational source, and then drew another circle comprised of different colors, where it is a spectrum from red to violet, violet representing faster rate of time, red representing a slower rate of time. Taking inverse square law into the equation, I showed how the rate of time changes correspondingly, to show that based upon location to a gravitational source, the rate of time changes.
Pretty neat. Just remember, there is no real "speed of time" Only "speed of time" as experienced by the observer. Also, remember space itself is also seemingly modified. Space and time are one and the (mostly) same in Relativity.
This is mind-bending stuff, which I wish I knew better, particularly the mathematics.
I've gone and tried to attempt to show how my brain is now configuring how space time is curved. I decided to draw a circle representing a gravitational source, and then drew another circle comprised of different colors, where it is a spectrum from red to violet, violet representing faster rate of time, red representing a slower rate of time. Taking inverse square law into the equation, I showed how the rate of time changes correspondingly, to show that based upon location to a gravitational source, the rate of time changes.
It seems as if you've got a few misconceptions. First, the inverse square law for gravity has NOTHING to do with general relativity. It's a product of 2 facts: First, we live in 3 spatial dimensions. Second, gravity emanates equally in all directions from a single point of matter.
These 2 facts alone account for the inverse square law (which Newton came up with also, and he never even thought about space time, or whether or not it could be curved).
Second, the fact that gravity slows time down doesn't show that spacetime is curved, because, for instance, a body moving at a high velocity has the same effect occuring, and again, it doesn't depend on space-time or curvature at all. The curvature of spacetime slows time down, not the other way around.
Rather, when space time is curved, it's also stretched (it's not compressed because flat space time is mathematically the minimum surface area needed. In otherwords, maximum compression of space-time occurs during flatness, so no configuration of matter, etc, can compress it more). When the stretching occurs, in some since "distance" (even in the time direction) is lengthened. Thus, it takes *longer* for one second to pass (as measured by an outside observer). So, to an outside observer, it looks as if time has slowed down.
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"Second, the fact that gravity slows time down doesn't show that spacetime is curved, because, for instance, a body moving at a high velocity has the same effect occuring, and again, it doesn't depend on space-time or curvature at all. The curvature of spacetime slows time down, not the other way around."
I remember that the faster one travels in relation to the speed of light, the more mass an object has, and of course, since E = mc^2, then mass, energy and speed are all tied in together.
If this is the case, then the curvature isn't gravity, the curvature is energy based upon mass, which also correlates to gravity, but not limited to gravity.
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quote:Originally posted by T_Smith: "Second, the fact that gravity slows time down doesn't show that spacetime is curved, because, for instance, a body moving at a high velocity has the same effect occuring, and again, it doesn't depend on space-time or curvature at all. The curvature of spacetime slows time down, not the other way around."
I remember that the faster one travels in relation to the speed of light, the more mass an object has, and of course, since E = mc^2, then mass, energy and speed are all tied in together.
If this is the case, then the curvature isn't gravity, the curvature is energy based upon mass, which also correlates to gravity, but not limited to gravity.
The thing is, even if you didn't have E=mc^2 to fall back on, the velocity STILL effects time. Also, an particle DOESN'T effect itself. What this means is that if somethings moving faster, sure it has more energy (and thus, more mass), so things are attracted to it more. Fine. But it's own gravitational field doesn't effect itself. To talk about gravity effecting time, you have to be talking about at least 2 things - the object (or science fiction device) creating the gravitational field, and the object being acted on. (Some may argue we also need an observor, but whatever)
To make this clearer, consider this little thought experiment.
We have two objects, H (for heavy) and F (for fast).
Now, assume that F is moving quickly relative to H (and assume H is stationary, just makes everything easier).
From our perspective, F's time slows down for 2 VERY different reasons. For one, H is massive, so it has a large gravitatoinal field. This field effects the curvature of spacetime which stretches out the time component of F's space time, making time move slower for F. Notice no where did we talk about the gravitational field of F. F's gravitational field will effect H, but it WILL NOT effect F.
But F's clocks also slow down because F is moving fast. Note that this would happen even if H wasn't there. This isn't a bending of spacetime, rather it's an effect of the fininte speed of light.
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I thought velocity itself is in correlation to C, which is the speed of light. Therein, spacetime is curved by energy due to either mass or speed of an object in reference to light.
Time = distance/speed of light
If so, I understand how gravity causes a curve in spacetime since it slows light. Velocity would change it then as well since light would appear to be going slower in reference to the object traveling closer to the speed of light.
All of this is back with spacetime, when I asked about gravity. Which I still don't get what is causing it.
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" when I asked about gravity. Which I still don't get what is causing it."
The short answer is we don't really know yet. Special relativity has properties that lead us understanding how gravity works... but no one knows what creates gravity. Gravity is a distortion in space time, and space-time curves when a mass is introduced, and we understand this mathematically, but we don't know what causes this.
Gravity is a field. There are also electro-magnetic fields. These are caused by the attraction and repulsion of charged particles. But there's no corresponding understanding for why there is a gravitational field.
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"Is it foolish of me then to refuse to accept the answer "it just is and does?""
For now, yeah. If you hold onto this too tightly, you won't let go.
Keep it filed away, though, for future analysis if you are so inclined. If you can tell the world what causes gravity, there's a nobel in it for you.
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quote:Originally posted by T_Smith: I thought velocity itself is in correlation to C, which is the speed of light. Therein, spacetime is curved by energy due to either mass or speed of an object in reference to light.
Time = distance/speed of light
If so, I understand how gravity causes a curve in spacetime since it slows light. Velocity would change it then as well since light would appear to be going slower in reference to the object traveling closer to the speed of light.
All of this is back with spacetime, when I asked about gravity. :) Which I still don't get what is causing it.
In your initial paragraph, you state, "Therein, spacetime is curved by energy due to either mass or speed of an object in reference to light." This is an ok way to think about things. Energy curves spacetime and mass and speed are two ways (out of lots) of getting energy. Fine.
Time = distance/speed of light only if the following hold: 1. We throw out relativity (both special and general). 2. Something is moving at the speed of light.
The more general equation time = distance/speed is ALSO incorrect. It's just that at slow speeds/normal gravity, it's close enough.
Next paragraph, you state, "If so, I understand how gravity causes a curve in spacetime since it slows light. Velocity would change it then as well since light would appear to be going slower in reference to the object traveling closer to the speed of light."
You just mentioned that ENERGY curves spacetime. energy is NOT the same thing as gravity. So this doesn't logically follow from what you just told me. Also, VELOCITY only changes space time if we're considering multiple object interactoins (this is what I tried to explain in my above post). In otherwords, if we're only interested in a single object (and the effects of the graviataional field on it), then the velocity of the object has NOTHING to do with the calculation curvature of spacetime.
Finally, your statement "Velocity would change it then as well since light would appear to be going slower in reference to the object traveling closer to the speed of light" is incorrect in what it argues. You're saying "if I move closer to the speed of light, then light will appear to move slower" This is exactly what Einstein's denied by postulating special relativity. That's what gives all these weird effects we're talking about now. Now matter HOW fast you are moving, if I shine a light at you, you ALWAYS meausre the speed of light to be 186,281.6 miles per second, even if you're moving 186,281.5 miles per second.
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quote:Next paragraph, you state, "If so, I understand how gravity causes a curve in spacetime since it slows light. Velocity would change it then as well since light would appear to be going slower in reference to the object traveling closer to the speed of light."
What I was saying is since mass curves spacetime, and gravity is a direct effect of the level of mass, that gravity is curving the space time. I suppose it is a bit innacurate to say that gravity itself is, then. More the mass that is creating the gravitational pull is curving spacetime, yes?
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quote:Did I understand this, or did I totally flub this?
Well, not totally. Say 50% flubness.
quote:Ok - so we have particles, that I am, for the most part, are taking down the level of an individual atom.
Atoms, nothing. Atoms are HUGE. Only boring nuclear physicists talk about atoms - well, actually, even they at least manage to concentrate on the nucleus. You practically have to talk to a chemist to hear about atoms, and who would want to do that? The action is at the level of quarks and electrons; quarks are the components of protons and neutrons, which make up the atomic nucleus.
However, none of this actually matters for the argument; my particle snobbery aside, you are perfectly at liberty to consider atoms.
quote:When you say boson, is that the previously mentioned messenger particle?
Yepyepyep. All messenger particles are bosons, that is to say, they have integer spin.
quote: Ok, so we have particles, spitting out and reabsorbing waves called bosons. Is a boson a wave or a particle?
Yes please, both, if possible.
quote:So we have a particle that sends out a boson, say particle exists at 0, and particle boson is headed to is at 10. Boson gets to 5 and gets called back to particle at 0, particle at 10 then gets pulled in the direction of the particle at 0.
Flubbity starts here. In the scenario you describe, there is no attraction; the boson has to actually reach the target particle to exert any influence on it. This, incidentally, accounts for the 1/r^2 strength of gravity and electromagnetism; basically, the further away a particle is, the less likely it is that the bosons manage to travel that far before getting reabsorbed.
Now, if the boson was travelling from 0 to 10 and got absorbed, that would be a repulsive force; it has to push the target particle in the direction it is going. So to account for attractive forces, we have to invoke QM; the boson can travel from 0 to 10, and still be absorbed by a particle sitting at -10. (This is not intuitive, and I realise that it contradicts what I said above about having to make contact. This is basically Heisenberg. Because the boson has a well-defined momentum, it doesn't really have a location. So we can say that it is going in the direction of 10, from 0; but at any given time, its position is best described as 'anywhere you like'. Therefore, it really is touching the particle at -10.) That pushes the absorbing particle in the positive direction, since that's the way the boson was going, which means it gets closer to the emitting particle - attraction, in other words.
quote:This then means that the more mass an object has, the more bosons it is emitting, and the more attraction it puts out.
Yepyepyep. Or in the case of electromagnetism, the more charge it has, the more bosons (in this case photons) it puts out. For the weak force, it's "the more hypercharge...", and the strong force is described in terms of two different charges collectively referred to as 'colour'. For the general case, we say the more "coupling to X" the particle has, the more bosons it puts out, where X is the kind of force in question.
Posts: 10645 | Registered: Jul 2004
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quote:Originally posted by T_Smith: Like Einsteins gold sheet thingy, right? Or was that some other dude? Do particles with wave-particle duality travel in a straight line, or do they follow the wave itself, going from crest to trough?
I think you mean Ernest Rutherford, but I have no idea what connection to mass or gravity you are making.
Waves and wave-like particles do not zig up and down. The wave represents the energy/intensity of the light/sound/particle, not its path.
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Ask what causes gravity, you get 5 responses in an hour, ask what time is, and you stump them all.
Posts: 9754 | Registered: Jul 2002
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Sorry about the delay in response (my in-laws are in town, gotta spend time with them!)
In GR, time (or more technically, Speed of Light * time) is simply another direction you can travel in, with one restriction - you can only go one way through time (no backwards time travel!).
As far as light (at least in the classical, non-quantum mechanics sense), light is a moving perterbation in an electromagnetic field. Think of it like this. If you're holding the end of a rope and you snap it really fast, a wave will travel down it. In this example, the rope represents the electromagnetic field and the wave represents the light.
In the quantum mechanics view, I know very little about what light is. I know they tend to model it more as a point particle, but in quantum mechanics, the rules of common sense are more or less thrown out, so a point particle of QM doesn't behave like an intuitive point particle does. I imagine photons still have something to do with fluctuations in an electromagnetic field, but at this point, I'm out of my league.
Posts: 168 | Registered: Jul 2006
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If you're looking for a good book on relativity and a number of other things, The Elegant Universe comes highly recommended from a number of my friends (I've not yet had a chance to read it, personally).
Also, another interesting tidbit: Einstein did not originally come up with the theories of special and general relativity. A Frenchman named Henri Poincaré published a paper detailing special relativity about five years before Einstein did, and he published a paper on general relativity a few weeks before Einstein. This is the same man who's famous conjecture was recently proven by Grigori Perelman, a Russian mathematician, and is considered to be one of the most important landmarks in the history of mathematics (since it's supposed to help to explain the nature of the universe, though I don't know enough details to explain more).
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I find that with GR it's not usually good to try to answer questions of the form 'What is X?' I much prefer just to plug the numbers into the equations. An intuitive understanding won't really help you anyway.
For the QM view of light, it's basically the same as in the classical view, except that the field is quantised and has to obey SR. Stick with photons and you'll be ok; the differences are highly technical and don't really matter unless you're doing actual calculations with the theory.
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