163 replies to this topic

[DukeNukem]

bgwonk, the issue is that while gravitation is of course well understood in terms of its effects in our universe, allowing us to precisely send ships to other planets, it is poorly understood in terms of its fundamental nature. Time, too, is both well understood, yet poorly understood. There can be huge books on both topics and yet neither book will explain the underlying nature of these two phenomena.

[jaydfox]

What Duke said.

[bgwowk]

Sure, there are foundational questions for all of physics. But like Maxwell's Equations, the development of General Relativity is a magnificent and monumental accomplishment of physics. In some of the rush to declare ignorance about gravity, I didn't want that overlooked.

Gravity is bent spacetime. But what is spacetime and why does it exist? How does one reconcile bent spacetime with a quantum interpretation? You got me.

[Lazarus Long]

Gravity is bent spacetime. But what is spacetime and why does it exist? How does one reconcile bent spacetime with a quantum interpretation? You got me

Brian that is the point. I at no time attempted to deny or ignore GR and second I happen to agree with you that if gravity propagates (an assumption in itself) that it does so probably at the speed of light.

The point about gravitons is simply we haven't yet found them and I also said that the wave characteristics of gravity are present but some aspects of that wave are still elusive. We have spaceships like GRACE out there to answer some of these questions.

http://www.csr.utexas.edu/grace/
http://www.csr.utexa...e/overview.html

http://www.csr.utexa.../grace/gravity/
http://www.scienceda...60804135910.htm

The wave characteristics of gravity are extremely long and still not precisely understood either though on this point we most certainly agree that there exists a more solid foundation and detection methodology to the theory.

I was simply presenting in a somewhat rushed manner another way to look at idea of curved spacetime as a force and it does not happen to contradict GR. What I said was that the mistake lies in trying to make our understanding of gravity fit our understanding of EM.

It is helpful to recognize that the universe does contain at least one kind of *duality,* or *polarity* of force (apart from positive & negative or hot and cold) described by what essentially are the two fundamental forces: EM as described by QM and gravity as described by GR. One describes extremely well the macroverse (cosmic scale) and the other the microverse (subatomic). One can be seen to determine the physics of the universe in a top/down fashion (or outside-in) and the other a bottom up fashion (inside-out).

If the classical understanding of the four fundamental forces turns out to be invalid as QM is now beginning to suggest by basically combining three of them into special cases of one (EM) then there are only two fundamental forces, one that is emanating outward from matter/energy and the other actually being directed inward toward matter/energy.

Looking at GR in this manner the spacetime curvature effect is (consistent with GR) understood as a *lens* focusing that *external force*, not attracting it from everywhere in the universe, not creating it and projecting it outward from the physical body. The more the mass and or velocity of an object, the more the lensing effect but the fabric of spacetime is not an aether but it could by this model be understood to be composed of gravity as a kind of background radiation and the presence of objects in that matrix alters the local spacetime relationship by creating wells of differing *depth* and *strength*.

I was trying to be careful about what I was saying we didn't understand and perhaps you assumed I was asserting we are totally ignorant, which we obviously aren't but the extent to which we do understand gravity based on QM models can be greatly overstated. GR not only works and has been validated time and again. However some of its premises do contradict some fundamental premises that QM depends on.

I am simply offering a kind of perspective meant to reconcile why that may be so. My point is to see the two as operating in a different polar direction *dimensionally* one expanding outward from the smallest to the largest and the other concentrating inward from largest to the smallest. The reason I proposed it also was to try and demonstrate *why* gravity should not be seen as *coming out of* a BH but rather pushing down into it through the curvature of spacetime.

BTW, the model I am proposing also can describe why we seem to be finding Dark Energy. I am suggesting that gravity is the fabric holding spacetime together (the coherent force of universal existence) and is ubiquitous throughout the universe not projecting or emanating at all from the masses present but it is concentrated in various degrees by the presence of matter and energy and their velocity. This model is not dependent on the total amount of mass to explain the total amount of gravitational force present and thus could explain the well documented difference between observations and predictions regarding universal expansion.

So IOW's if we instead try and describe the universal gravitational constant as a result of its total size of the universe and not strictly in terms of the masses present we might see the measurable quantity of Dark Energy can be explained simply as an extra amount of *gravity* resulting from the added volume of spacetime. This would be in accord with our observations and I suspect can be mathematically applied to support the idea. We don't need a lot of Dark Matter to explain the Dark Energy, only the increased total size of spacetime.

BTW this is consistent also with recent observations finding that Hubble's constant is about 15% off and the universe is older and larger (currently about 180 billion LY's across) than what what was previously thought.

http://www.space.com...ble_revise.html

To simplify this perspective it is probably better to see the universe as pushing down on matter/energy rather than matter/energy pulling at the universe. This not does not deny the validity of GR at all and in fact supports it but it alters our understanding slightly of what is creating the *force* known as gravity. It is certainly consistent with *why* anything *falls down* a gravity well. )

And why increasing mass (and/or velocity) acts to focus greater and greater amounts of gravity into stronger and stronger such wells through its lensing effect. It doesn't however alter the observed relationships of gravity and matter, only what the source (directionality) of the fundamental force is and why gravity could perhaps be said to be increasing in strength in accord with the inverse square law the closer to the center of mass you get rather than diminishing the farther you get away from it.

[bgwowk]

Laz wrote:

GR not only works and has been validated time and again. However some of its premises do contradict some fundamental premises that QM depends on.

Of course that doesn't mean GR is wrong, just that its scope of applicabilty is limited, like most other physical theories. The only really "finished" physical theory is quantum electrodynamics (QED -cool that they named it that way) in that it gives correct answers to unlimited decimal places so far.

BTW this is consistent also with recent observations finding that Hubble's constant is about 15% off and the universe is older and larger (currently about 180 billion LY's across) than what what was previously thought.

As a point of interest, 180 billion light years would be the present distance of the matter that 15 billion years ago generated cosmic microwave background photons we see today. If cosmological inflation really happened during the early moments of the universe, the real size of the universe is much larger than that. We can just never see those farther parts. If we can't ever see something, does it really exist? It's one of those if-a-tree-falls-in-a-northern-forest-and-no-one-hears-it kind of questions.

Unfortunately I don't know enough about gravity or cosmology to comment on your gravity-as-a-repulsive-force theory, except to offer the general warning that to walk beyond what is proposed or speculated by experts without being an expert too is to walk on thin ice.

[jaydfox]

. We can just never see those farther parts. If we can't ever see something, does it really exist?

If the universe stopped expanding, or slowed sufficiently, then couldn't we eventually see those other parts, even if it's hundreds of billions of years from now?

You know, ignoring the fate of the universe between now and then (catastrophic expansion, collapse, etc.).

[bgwowk]

If the universe stopped expanding, or slowed sufficiently, then couldn't we eventually see those other parts, even if it's hundreds of billions of years from now?

Yes, if there's anything left other than brown dwarfs by the time you get there. Or maybe somebody will have converted it to computronium, just like all that space behind you.

[tadas]

Light is only the fastest measured speed. There may be other movements which we can't or have not measured that could be faster than light.

[Centurion]

Isn't the current course toward defeating gravity an attempt to ascertain the frequency of a gravity wave and then counter it with an opposite wave? Hence the experiments into super heavy elements like ununpentium which may slow gravity down to the point where it can be observed.

[jaydfox]

Isn't the current course toward defeating gravity an attempt to ascertain the frequency of a gravity wave and then counter it with an opposite wave? Hence the experiments into super heavy elements like ununpentium which may slow gravity down to the point where it can be observed.

[huh]

[jaydfox]

I just realized, we need a [wtf] smilie.

[Centurion]

[cry] lol, we arent all great scientific minds.

I read something to that effect a few years ago on an amateur site somewhere. I bought it, I don't know a lot about anything sadly

[caston]

I'd like to propose that light is actually the slowest thing in the universe. Matter on the other hand travels through time at what we consider to be the speed of light.

What we need for computational biology is a machine that travels through time slower than we do. Perhaps photonics is the best way to achieve this?

I asked Garth from Physicsforums.com about my proposal and he said "It sounds as if you have got time dilation back to front. Try studying an introductory course on SR and then try again!"

He is right I should study special relativity and I would love to find some way of testing this theory. We once believed that that sun revolved around the earth did we not?

Edited by caston, 07 November 2006 - 05:58 AM.

[xanadu]

There are things that move faster than the speed of light. Thought being one of them. We can go from one end of the universe to the other in a jiffy in our thoughts. If you had a flashlight that would illuminate planets, you could send your beam from one planet to the other in a time that would equal a FTL speed. But this is an illusion.

Dukenukem wrote:

"bgwonk, the issue is that while gravitation is of course well understood in terms of its effects in our universe, allowing us to precisely send ships to other planets, it is poorly understood in terms of its fundamental nature. Time, too, is both well understood, yet poorly understood. There can be huge books on both topics and yet neither book will explain the underlying nature of these two phenomena."

Very well said, Duke! There is a tendency among humans in general and among scientists in particular to think that if you name something you then know a great deal about it and if you have calculations that describe it, you then understand it's fundemental nature. We do not completely understand any of the fundemental forces of nature least of all gravity. Another tendency is to assume that if you have a theory that attempts to explain something then you have it figured out. If your theory produces predictions that can be tested and if they do come to pass in the real world, then you do have something. You do not however have a complete understanding of the phenomenon but you have clearly made progress toward that goal.

What then of theories that do not produce any testable predictions or whose predictions do not consistantly gibe with the results observed? Do those theories bring us closer to a true understanding of the universe or are they little more than mental excercises? I commited the faux pas of calling such theories "fairy tales" which is perhaps too blunt. If they lead to theories that work, then you could go back and make a case that they had some value though they were not correct in their form at that time.

caston wrote:

"What we need for computational biology is a machine that travels through time slower than we do. Perhaps photonics is the best way to achieve this?"

We know that time is relative and can be slowed by relative speed. It is theorised that time is greatly slowed or dilated inside a black hole. This may serve the purpose of slowing time but it is very hard or impossible to get out of the black hole not to mention the difficulty (heating, etc) of getting inside. It has been theorised by myself and others that our universe is itself a black hole. That is to say that the mass of the universe has caused space and time to close in on itself. As a result, our universe may be totally endless and unbounded but be finite in size.

[eternaltraveler]

There are things that move faster than the speed of light. Thought being one of them.

I believe the fastest conduction speed in axons in nature is less than 100 m/s )

If you had a flashlight that would illuminate planets, you could send your beam from one planet to the other in a time that would equal a FTL speed. But this is an illusion.

what? If I tried to illuminate the moon with a giant flashlight I wouldn't see the moon light up for 2.6 seconds after I turned on the flashlight. The moon is 1.3 light seconds away.

It has been theorised by myself and others that our universe is itself a black hole. That is to say that the mass of the universe has caused space and time to close in on itself. As a result, our universe may be totally endless and unbounded but be finite in size.

that doesn't jive with the observation that the universe is not only expanding, but it's rate of expansion is accelerating

[jaydfox]

If you had a flashlight that would illuminate planets, you could send your beam from one planet to the other in a time that would equal a FTL speed. But this is an illusion.

what? If I tried to illuminate the moon with a giant flashlight I wouldn't see the moon light up for 2.6 seconds after I turned on the flashlight. The moon is 1.3 light seconds away.

I think he's referring to the sweeping of a beam, such that at great distances, the beam appears to sweep FTL. And he's right, it's an illusion; nothing physical is actually travelling FTL, just the conceptual "spot" illuminated by the beam.

[eternaltraveler]

I think he's referring to the sweeping of a beam, such that at great distances, the beam appears to sweep FTL. And he's right, it's an illusion; nothing physical is actually travelling FTL, just the conceptual "spot" illuminated by the beam.

ah

[caston]

We know that time is relative and can be slowed by relative speed. It is theorised that time is greatly slowed or dilated inside a black hole. This may serve the purpose of slowing time but it is very hard or impossible to get out of the black hole not to mention the difficulty (heating, etc) of getting inside. It has been theorised by myself and others that our universe is itself a black hole. That is to say that the mass of the universe has caused space and time to close in on itself. As a result, our universe may be totally endless and unbounded but be finite in size.

Could we somehow do this without the problematic blackhole?

I have heard of projects to simulate small blackholes. Perhaps *somehow* a computer could operate inside the blackhole with prescripted caclulations to run. Hopefully the blackhole will close but still leave the finished information ready for us to look at.

People talk about encryption schemes that would take until the death of Sol to break using a bruteforce method but what if the machine working on it was travelling through time at 1 m /s instead of 299 792 458 m / s?

What if a biological simulation that would take 300 years to complete on a commodity dual core processor machine was carried out on of a machine that was made to travel through time 100,000 times slower?

Does electricity traveling through a sea of delocalised electrons within a conductor make that conductor travel through time slower?

Do enthuiasts spend thousands of dollars on their cars just so that they can travel through time a little slower?

Check out the following article "Abstract geometrical computation for Black hole computation":
http://www.ens-lyon....4/RR2004-15.pdf

Edited by caston, 08 November 2006 - 08:19 AM.

[mitkat]

People talk about encryption schemes that would take until the death of Sol to break using a bruteforce method but what if the machine working on it was travelling through time at 1 m /s instead of  299 792 458 m / s?

What if a biological simulation that would take 300 years to complete on a commodity dual core processor machine was carried out on of a machine that was made to travel through time 100,000 times slower?

This is a serious idea! It's fantastical, but when contrasted with everything else in this thread, it seems totally reasonable to think this could be possible.

[xanadu]

elrond wrote:

"I believe the fastest conduction speed in axons in nature is less than 100 m/s"

You are missing the point by being too literal and nuts and bolts oriented. Same with the flashlight beam experiment. We can think of the sun and then think of the earth a moment later beating light's time from sun to earth

caston wrote:

"I have heard of projects to simulate small blackholes. Perhaps *somehow* a computer could operate inside the blackhole with prescripted caclulations to run. Hopefully the blackhole will close but still leave the finished information ready for us to look at."

How do you simulate a black hole? That's a new one on me.

"Does electricity traveling through a sea of delocalised electrons within a conductor make that conductor travel through time slower?"

Electricity does not move physical objects at or near the speed of light. Actual electrons move very little, it is the electrical force that moves. It's sort of like a wave moving over a pond. The wave has energy and can move fast but the individual water molecules stay in roughly the same place.

[caston]

Thanks Xanadu: I'm still learning chemistry as you can see.

About the blackholes: I found a few articles using a simple google search:

http://www.google.co...G=Google Search

[xanadu]

Good find, caston. I had not heard about the black hole making project. Fortunately, if they are sucessful in creating artificial black holes, they will be smaller than an atom and have not enough mass to start swallowing the earth like a larger black hole might be able to. But, if they do not evaporate they could swallow slowly subatomic particles and work their way up to atoms and finally the earth. Once a black hole gets started there is little that can stop it. If one falls to earth from space, we are doomed.

What gets me is that hawking radiation is constantly referred to as though it really exists when it exists only in theorry and has not been observed.

[jaydfox]

But, if they do not evaporate they could swallow slowly subatomic particles and work their way up to atoms and finally the earth. Once a black hole gets started there is little that can stop it. If one falls to earth from space, we are doomed.

Luckily, such a small black hole would take a very, very long time to swallow the earth. Probably billions, if not trillions of years. At first, its surface area would be smaller than a proton: it would have a hard time swallowing the occasional atom.

By the time the black hole could work itself up to the size of a large atom (say, a nanometer in diameter), it would have a mass oon the order of 10^15 kg, the merest fraction of the earth's mass. At that size, even if we assumed that material was being sucked in at the speed of light, through a surface area of about 12.5 nm^2, the rate of mass consumption would only be about:
1.25x10^-17 m^2 * 3x10^8 m/s = 3.8x10^-9 m^3/s

That's 4 cubic millimeters per second. That's nothing. After a billion seconds, about 30 years, that's four cubic meters. Still nothing. After 30 million years, that'd be 4 million cubic meters, less material than is spewed from a large volcanic eruption.

We don't need to worry about black holes this small, even if Hawking radiation doesn't exist.

[xanadu]

"At first, its surface area would be smaller than a proton: it would have a hard time swallowing the occasional atom."

That is making many assumptions. The gravity of the BH may be small but it may have electrical charge or something else that attracts particles and atoms.

"That's 4 cubic millimeters per second. That's nothing. After a billion seconds, about 30 years, that's four cubic meters. Still nothing."

You are assuming the rate of accretion does not accelerate during that time. Naturaly it would accelerate. At some point, the earth's mass would be in free fall toward the BH or forming an accretion disc. None of that would be healthful for the earth's inhabitants.

The fact that the earth and other planets as well as the sun have not been gobbled by a BH may mean our fears are groundless or may mean no BH has come our way. Perhaps they are harder to create in the lab than we think. I would suspect that jupiter would have created bunches of them if it was that easy to do.

[jaydfox]

"That's 4 cubic millimeters per second. That's nothing. After a billion seconds, about 30 years, that's four cubic meters. Still nothing."

You are assuming the rate of accretion does not accelerate during that time. Naturaly it would accelerate.

Well, yeah. Of course it would accelerate. By the time the black hole could double in mass, it would have four times the surface area, so the rate of mass consumption would increase by a factor of four. So four cubic millimeters per second would go up to 16 cubic millimeters per second! To get a lower bound on the time it would take to double in mass from 10^15 kg to 2x10^15 kg, let's assume the full 16 cubic millimeters per second, and let's assume a density of 25 grams per cubic centimeter.

At 1.6*10^-8 m^3/s * 2.5*10^4 kg/m^3, we get 4*10^-4 kg/s. So it would take about, oh, 2.5*10^18 seconds to double in mass, as a lower bound. That's billions of years, to accelerate by a factor of four. The next factor of four would take half the time (twice the mass through four times the surface area), so the acceleration itself would accelerate. But it would take billions of years before the acceleration had any meaningful effect.

The bottom line is, a black hole this small is effectively insignificant, at least as far as the fate of earth is concerned.

[DukeNukem]

Yeah, small black holes (in terms of their event horizon) are harmless, as they would nearly instantly evaporate (Hawking's radiation to the rescue), and they would not have the gravitational reach to bother anything or anyone. We could release 100,000 trillion into our atmosphere and no one would ever know. You could release an even bigger black hole, say basketball sized, in the middle of Earth's core, and likely nothing would happen. The basketball sized black hole simply could not grow fast enough because the material it's sucking in would not add to its size enough to make a difference. It would just carve out little tunnels for 100's maybe 1000's of years. At least, that's my guess -- I might be waaaaay off because I haven't done a lick of math on this.

[xanadu]

Jay, your math skills are impeccable but your assumptions are way way off. What we don't know is how it will react when very tiny. If it's unable to pull in matter then it may never grow. However, if it does pull in matter at all, we do not know how fast it will grow. To say it would take billions of years to double in size makes no sense.

Lets take the example of a BH the size of a grain of sand, or since size is somewhat irrelevent for BH's, a BH large enough to interact with surrounding matter. It may be the size of one micron in it's event horizon. This BH is going to tend to go to the center of the earth. As it presses against earth, rock and so on, it will absorb them into it's interior. A BH the size of a micron may grow to a basketball size in a matter of hours, not years. It may be faster than that. Why should it not absorb all matter that touches it even before it's gravity is enough to pull things to it? Once it reaches the center of the earth, it would rapidly absorb the entire earth as fast as the matter of the earth can fall in.

When it's the size of a subatomic particle it may take a very long time to grow or not grow at all. That would likely depend on electrical charges and other forces in the way they interact with it. Since Hawking radiation has never been observed, I would not rely on it to save us. Like I say, it's probably a lot harder to produce them than is thought. If it was easy then they would be produced naturally in the sun or in jupiter or even smaller planets. Since none of them have been gobbled up, it's either much harder to do or the tinyBH's can not grow due to some repulsion that keeps them from drawing in other matter. Perhaps dark matter is composed of such micro BH's?

[DukeNukem]

>>> As it presses against earth, rock and so on, it will absorb them into it's interior.

A BH doesn't grow fast -- I takes a LOT of matter to make any significant growth. A BH with an event horizon the size of a grain of sand (as opposed to a BH made from matter the equivalent to a grain of sand, which would likely be smaller than a proton) would suck down very little matter on it's 30 hour journey falling to the center of the earth, where it would get stuck, barely making any impact on it's surroundings. (At least, this is my guess.)

[jaydfox]

Well, for one thing, a basketball-sized black hole would weight about 15 times as much as the earth, give or take, so it would be extraordinarily bad, but for other reasons besides sucking in the earth.

A black hole with 1% of earth's mass would be about 200 microns across. By virtue of its mass (i.e., regardless of the fact that it was a black hole), it would increase gravity at the earth's surface by 1%, which would have some pretty noticeable consequences (pressures would increase at all depth by 1%, and even more near the core), which would compress and shift material around and cause seismic activity. The seismic consequences of a black hole that big dropping from the earth's surface to the core are far worse than the prospect of material disappearing into the black hole.

A black hole of the size we might create in a lab (assuming it even happens) is so small that, even if it didn't spontaneously explode from Hawking radiation, it would nonetheless be, for all practical intents and purposes, completely harmless.

[jaydfox]

As it presses against earth, rock and so on, it will absorb them into it's interior. A BH the size of a micron may grow to a basketball size in a matter of hours, not years. It may be faster than that.

Well, let's keep it simple: it can't suck matter in faster than the speed of light. Given a well-defined surface area, using the speed of light as the rate at which matter is sucked in (it might be less, but it's certainly no more), and given an arbitrary density for matter, we can set an upper bound on how fast a black hole can suck matter in.

Yes, conceptually, it seems like a black hole could grow quite quickly.

So here's an example that maybe you can wrap your intuition around. Let's make a bathtub the size of the ocean, with a standard sized drain. Now pull the plug on the drain. How long will it take to empty?

Regardless of the fact that the tub might be miles deep, it's not going to drain in a few minutes, or even a few hours. It will take a very long time. Why? Because the drain is so small. You simply can't force an entire ocean through a drain, no matter how fast the drain is sucking down water. There's a practical limit to how fast water can get out of the way so more water can go through the drain.