gabby, most of what you wrote was right on, but you lost it when you started claiming that everything is getting larger. The Universe is getting bigger, but the matter it contains is staying the same size. You see, gravity counteracts the expansion force. Where there is matter, there is gravity. Where there is gravity, there is little or no expansion. Where there is mucho gravity, there is contraction (a black hole).
The universe is expanding, but mostly in (nearly) empty intergalactic space where gravity is practically non-existant. (I say nearly because space is never totally empty. There are always a few stray particles floating about.) As empty space comes into being, the galaxies get further apart.
I can’t imagine how the speed of light in a vacuum could ever change.
gabby, most of what you wrote was right on, but you lost it when you started claiming that everything is getting larger. The Universe is getting bigger, but the matter it contains is staying the same size. You see, gravity counteracts the expansion force. Where there is matter, there is gravity. Where there is gravity, there is little or no expansion. Where there is mucho gravity, there is contraction (a black hole).
The universe is expanding, but mostly in (nearly) empty intergalactic space where gravity is practically non-existant. (I say nearly because space is never totally empty. There are always a few stray particles floating about.) As empty space comes into being, the galaxies get further apart.
I can’t imagine how the speed of light in a vacuum could ever change.
gabbyhayes, if the expansion of the universe were the cause of gravity, the surface gravity of Moons and Planets would vary proportionally to their diameters, and would not depend on mass. This is not the case.
Actually, there is no upper limit to how fast something can recede. The further away something is, the faster it is receeding.
32.2 feet / sec[sup]2[/sup] is the acceleration due to gravity here on earth, this has nothing to do with the expansion of the universe.
No, NO NO!!! In order to say something is getting larger, you must say larger as compared to something in the universe. It is not meaningful to say that everything in the universe is expanding. Expanding compared to … what?
HUH? Beyound a certain point (I’d call it an event horizon) the recession velocity is the speed of light or greater. Nothing beyound this horizon can ever reach us. The light doesn’t stop and it certainly doesn’t “become matter”.
Could someone please translate gabbyhayes’ post for me? I’d like to comment on it, but I have no clue what he/she is trying to say. Zenster, the work isn’t done by the gravitons, it’s done by whatever lifted the object. It doesn’t matter how gravity works, or whether it involves gravitons. Unfortuantely, I can’t explain exactly how gravitons work, because nobody really understands it yet. The reason that we postulate the existance of gravitons is that we’d like to be able to discuss gravity in the same way as we do electromagnetism, and we know that EM is mediatied by the photon. We can say a few things about what the nature of the graviton must be, based on what we know of gravity: For instance, since gravitational effects propagate at the speed of light, the graviton must be massless, and because it’s a tensor field, not a vector field like EM, the graviton must have a spin of 2, unlike most fundamental particles with a spin of 1/2 or 1. It’s presumed that gravitational waves are quantized like light waves, and if so, then the quantum of gravity waves would be the graviton.
The usual metaphor for how particles can mediate forces is a couple of people standing on ice (frictionless, of course), and tossing a basketball back and forth, thus pushing each other apart. Of course, in order to get an attractive force out of this, your basketball needs to have a momentum opposite the direction of its motion, but in the weird quantum world of virtual particles, this is allowed.
The rubber sheet analogy does have some major flaws, but it is, after all, only an analogy. The core idea is that in curved spacetime, matter travels on the equivalent of straight lines (called “geodesics”), but due to the curvature, these “straight” geodesics end up looking like they’re curved.
I have to say I’m a little skeptical about the “rubber sheet” explanation. As was alluded to by other posters, the “rubber sheet” postulates a “meta-gravity” and thus begs the question. It’s sort of like saying that the universe rests on the back of a giant turtle. Fine, but what’s the turtle standing on?
That said, I must say that I am inclined to believe that gravity is due to the curvature of space-time. I believe this because different objects (including light) seem to fall at about the same rate (if they’re in the same place). This suggests that either (1) the objects are following a uniform curve in space-time; or (2) for some reason, weight (gravitational attraction) is exactly proportional to inertia (resistance to acceleration), regardless of the type of object involved. Number 1 is a simpler explanation to my mind.
My questions are as follows:
(a) can somebody give me an explanation of gravity (or curvature) that doesn’t have the nasty problem of meta-gravity?
(b) if space-time is curved, are there any other observable effects beyond the good old gravity we’ve come to know and love?
The Hindu theory that the universe rests on the back of a turtle, that stands on the back of a water buffalo, that stands on the back of an elephant has been disproven completely…
It’s turtles all the way down…
PS: lucwarm, there is no “meta-gravity” involved in the rubber sheet analogy (please refer to my previous post). What you are perceiving as “meta-gravity” distorting the rubber sheet, is matter warping space time.
“PS: lucwarm, there is no “meta-gravity” involved in the rubber sheet analogy (please refer to my previous post). What you are perceiving as “meta-gravity” distorting the rubber sheet, is matter warping space time.”
Suppose you set up the rubber sheet experiment on Space Station Mir (or whatever, some place that is in “free fall”). The small ball won’t move any closer to the big ball. IMHO, there’s something circular about a metaphor for gravity if the metaphor requires gravity to work properly.
Can space-time be warped without the presence of matter? If there’s matter around, can space-time be straightened out? If the answer to both questions is “no,” then there’s something wrong with the theory. You might as well say, “gravity is caused by the invisible pink unicorn, which likes to hang around in the presence of matter.”
P.S. I’m inclined to view gravity as a warping of spacetime, but it seems to me that this explanation is unfalsifiable. It seems really more an interpretation than an explanation. Please describe an experiment that would decide the question.
thanks Chronos and all the rest, for providing many interesting theories, and false pathways, for me to wander in. I’m also grateful noone mentioned one particular theory: “there is no gravity, the universe just sucks”.
btw, my name is derived from the old space opera “lensmen” series by E.E. Smith. He appeared in 1 or 2 paragraphs, but tickled my fancy
When you said matter did you perhaps mean light? Light traces geodesics, not matter. A geodesic is the closest thing you can have to a straight line in curved space. (If space is flat geodesics are exactly straight lines.)
(a)Maybe someone else can, but not me.
(b)There is a way to detect curvature of space without looking from a higher dimension or even assuming the existence of a higher dimensional space. If the curvature of space is positive, a triangle will have more than 180 degrees and less than 270. The smaller the triangle and the flatter the space, the closer you get to 180. If the curvature of space is negative a triangle will have less than 180 degrees. Since we are so small relative to the universe, we would have to construct very large triangles to detect the curvature this way, but it is possible using light beams to form the legs of the triangle.
There is a classic book Flatland - a Romance of Many Dimensions by Edwin A. Abbot written in 1880 that takes place mostly in a plane. The difficulty the inhabitants have in understanding a third dimension helps the reader understand higher dimensions. After Flatland was written, it was discovered that space was curved and expanding. Sphereland A Fantasy About Curved Spaces and an Expanding Universe by Dionys Burger written in 1960 is a sequel to Flatland where the inhabitants realize that their 2D space is really curved and expanding. I recommend them both highly.
Zenster
The rubber sheet analogy does depend upon meta-gravity. It uses a familiar concept (stretching of a sheet due to objects placed on it) to help visualize an unfamiliar concept (the stretching of space due to the presence of mass). There is no need to explain the meta-gravity, but it is there.
What do you mean by “strength” of the gravity well? And how are the “three spatial dimensions…integrated into” two dimensions? The sheet is two dimensional, not three. I don’t understand this.
It’s easy because the internet is expanding faster than the universe. Or maybe it’s the other way around.
What happened is I got that “unintelligible response” notice after I hit “Submit Reply” the first time, so I thought it meant my post did not go through. I hit “Refresh” to see if it had, and the thread still looked the same. So I hit “Submit Reply” again. I got “unintelligible response” again. I hit “Refresh” again. The post STILL wasn’t there. I hit “Submit Reply” a third time. I got “unintelligible response” a third time. I hit “Refresh” a third time. My post STILL wasn’t there. Lather, rinse, repeat.
I gave up and went to another thread. Later, I returned to this forum, saw that I was credited with the last post, looked at the thread, and saw, to my embarrassment and horror, a triple-post.
I had forgotten the dictum, “Trust the php!” Even if you don’t see it right away, the post ALWAYS goes through.
You may now return to your regularly-scheduled discussion/lecture.
Actually, DrMatrix, we needn’t build triangles light-years to a side to determine the shape of the universe. CalTech and JPL found an easier way: They launched a balloon high above Antarctica carrying a telescope named “Boomerang” designed to measure the cosmic microwave background. According to its findings, the universe IS flat. Straight lines are always straight, parallel lines never converge and the angles of a triangle, no matter how large, always add up to 180 degrees. It also means that “rubber sheet” analogy is actually pretty accurate.
Triple post, Bah! I had a quintuple post once. TubaDiva suggested that I never ever do it again.
Thanks for the links, jab1. I don’t how this proves the universe is flat; just that, if it is not flat, the radius of curvature must be very large. Locally, matter bends space to give it a negative curvature even if the global curvature is flat.
The rubber sheet analogy that I gave was not ment to use Meta-Gravity as stated above. It was to explain it in layman terms. If you want more information on it then you need to get out of layman terms and start doing some heavy math (pun unintended). Here is a great link for math/physics/chemistry questions http://www.treasure-troves.com For more info on mass bending space-time look here http://www.treasure-troves.com/physics/GeneralRelativity.html Follow the links on gravitational lensing and gravitational waves. Once again the question asked for layman terms, which simplifies things, sometimes too much.
you can’t say definitively that matter isn’t expanding. There is no reliable way to measure it, since yardsticks are also expanding. The notion that light travels at a constant speed can only be verified by taking a known distance and measuring the time it takes to traverse it. If the distance is expanding at an accelerating rate, but the light takes the same length of time to traverse it, light is accelerating at the same rate that space is expanding. The mass of an object is directly related to its density, which is the amount of matter as a proportion of the amount of space it takes up. If the space expands at the same rate as the matter, well that is a problem with my theory but one that is less troubling than orbits, which would then become outwardly winding spirals. Both might be explained by some other characteristic such as a bow-wave effect on space as objects expand. However, if space is expanding at the same rate as matter, there should be no bow wave. Perhaps there is some built in principle that causes perterbations at the interface of space and matter–something like surface tension. An expanding object might form a meniscus.
Our only experience with gravity is pretty local. No one has wandered more than 250,000 miles from earth. We might discover things on Mars that conflict with our commonly understood notions about gravity. I should point out that we’ve had terrible luck with landing craft on Mars. Sometimes it’s attributed to bad programming, but sometimes the reason is completely unknown. It may be because we completely misunderstand the effects of gravity on an earth-sized planet with no iron core.
Anyway, it’s good to take a step back from time to time and entertain the possibility that everything we take on faith about the physical laws of the universe is flat wrong and some completely different set of laws is actually at work.
One of the theories I like is that there is a repulsive force in the universe and that massive objects block the repulsive force, thus giving the illusion of gravity.
Gabbyhayes,
You need to take some science lessons. First off there is no faith in science. All science theories are constantly questioned and tested.
Secondly the math of gravity is proven and holds true throughout the universe, so far. It is comming up with a model that explains the math that is the hard part. The math doesn’t change on Mars. Our experience with gravity is not local. We can observe the effects of gravity on solar sytems out side of our own. Iron has nothing to do with gravity.
Matter is not expanding. The universe is expanding ie the distance between celestrial objects. The mass and length of matter only expands when it is moving at a constant velocity and is only noticible at speeds close to the speed of light.
Light does not accelerate. It has a constant speed for all frames of reference.
We can observe the effects of gravity throughout the universe and it works the same everywhere. We can predict the orbit of Pluto (or distant orbiting stars, or distant orbiting galaxies) using the same method that we would for the Earth’s orbit around the sun.
Although no human has directly experienced gravity beyond the distance of the moon, we do have direct measurements from the many spacecraft that we have sent to the more distant planets (and even beyond Pluto).
Your statement that "we’ve had terrible luck with landing craft on Mars…sometimes it’s attributed to bad programming, but sometimes the reason is completely unknown. " is misleading. Although there have been some lost missions with no explanations, other losses have been satisfactorily explained, and there have also been several complete successes. Getting a craft to Mars requires precise calculations that involve gravity, so the fact that we’ve hit it right-on more than once shows that it’s reliable.
When astronomers take measurements of the universe, they see space expanding, not matter, and not collections of matter (i.e., solar systems do not expand, galaxies do not expand).
The “repulsive force” you mention sounds like the cosmological constant, which does not conflict the current theories on gravity.
Like WiredGuy said, I’d recommend that you read the science texts for the evidence supporting current theories (it’s not based on faith) and then try to find evidence to support your ideas.
[QUOTE]
*Originally posted by Phobos *
**gabbyhayes - I agree with WiredGuy
and there have also been several complete successes. Getting a craft to Mars requires precise calculations that involve gravity, so the fact that we’ve hit it right-on more than once shows that it’s reliable.
[joke] This is because Mars expanded until it safely mated with the landing craft. Had Mars remained a constant size then the landing craft would have crashed into it.[/joke]
Seriously though, the idea that everything is expanding is easily dispelled by using spacial relations. Two objects with static static displacement relative to one another (such as our moon and our earth) will meet if both expand unless they change relative positions. If you apply this to stellar mechanics then the orbits which are easily observed down to the picosecond would alter at an exponential rate.
Another way of looking at this: If the Earth and the moon were both expanding then the moon and the earth would have to move away from one another at an exponential rate of speed.
Another think I had on this, continual expansion at the sub-atomic level would be required even if you throw away the rest of the physics. What this means is that the bonds between electrons would have to get stronger and stronger. This would require energy on an unlimited scale. Limited matter cannot generate unlimited energy. There is no such thing as a Genesis Device and there never will be. Mass energy conversion is finite except in Wonderland.
Everything, be it matter or light, traces out geodesics in space-time if under the influence of no force other than gravity. If you just look at the space components of an object’s motion, however, you don’t get a geodesic: You need to include time, as well. The “shortest” path from this side of the Earth’s orbit now to the opposite side now is through the Sun, but the shortest path from here/now to the opposite side of the orbit six months from now is along the orbit. (I put “shortest” in quotes, because the definition of distance is a little different in 3+1 dimensions than it is in 3 dimensions.)
The Boomerang measurements do, indeed, only show that the radius of curvature is very large, not that it’s necessarily exactly flat. It’s close enough to flat, though, that we’re not likely to ever see any effects from curvature: Boomerang is already looking at triangles on the largest size scale we can possibly see.