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Ok, let me try to address these: > Black holes don't exist (time dilation prevents them from forming in a finite time) It's true that distant observers cannot

Ok, let me try to address these: > Black holes don't exist (time dilation prevents them from forming in a finite time) It's true that distant observers cannot observe anything past the event horizon. But if you doubt that a black hole exists, you can always dive into it; the black hole will then certainly exist for you, and in a finite time. > Dark matter is gravitational potential energy Consider the Bullet Cluster, which is two colliding galactic clusters. The gravitational center of mass is offset from the visible center of mass. This offset cannot be explained as potential energy of visible matter. There must be something else, invisible and massive, i.e. dark matter. > Cosmological redshift is actually gravitational redshift We see cosmological redshift in all directions. If this redshift were gravitational, it would imply that our galaxy is at the top of a gravitational potential hill. This means that our place in the universe is very privileged, which is unlikely.

justifier 10y ago
> Consider the Bullet Cluster, which is two colliding galactic clusters. The gravitational center of mass is offset from the visible center of mass. This offset cannot be explained as potential energy of visible matter. There must be something else, invisible and massive, i.e. dark matter. i'd argue another possible explanation to add to your i.e. was addressed by the gp gp> then galaxies are not moving in the way we currently think they are. the movement of gyroscopes can alter a system's center of mass https://www.youtube.com/watch?v=n_6p-1J551Y https://www.youtube.com/watch?v=n_6p-1J551Y
- dhimes 10y ago
  The rotation is the gyroscope. And the meaning of your last statement (the movement of gyroscopes) is unclear. The video is cool, but well understood by the same physics that is being applied to the understanding of the galaxies.
  - justifier 10y ago
    exactly, but the gp threw in the caveat gp> then galaxies are not moving in the way we currently think they are. so if our calculations already take into account the gyroscopic movement of the bodies within the system, still the gp's thought experiment accounted for this by saying the real nature of the motion of the bodies is different than the motion that we are currently using in our calculations just saying dark matter ignores the potential for other valid explanation for the phenomena instead of there being dm offsetting the center of mass the gyroscopic motion of the bodies within the system also could explain the offset 'not moving in the way we currently think' is a vague statement and could be a direction of rigor for the gp if thae wished to pursue the idea some underlying questions that need to be answered by anyone that suggests our current understanding is incorrect in this regard would need to address: how are they moving differently? how could we detect the difference? how can our incorrect perception be explained? my> the movement of gyroscopes can alter a system's center of mass the cube video was intended to show that yes, this is well understood, and exhibit how changing the nature of the rotation of the gyros: location, direction, speed; in the cube you could move the center of mass to wherever you'd like add another dimension allowing the gyros to move freely stead being fixed within a cube and even more freedom to alter the center of mass could be achieved https://www.youtube.com/watch?v=UnpLEnIqj_A https://www.youtube.com/watch?v=UnpLEnIqj_A i agree it is well understood.. that is why i was using it as naive evidence to defend the gp's thought experiment from being dismissed poorly
    - dhimes 10y ago
      add another dimension allowing the gyros to move freely stead being fixed within a cube and even more freedom to alter the center of mass could be achieved It's the fact that it is fixed within the cube that allows it to move the cm. That only happens because of the reaction force it can exert against the ground. In the absence of external forces the cm won't move (strictly, won't accelerate). In a sense this is a tautology. So it's not an uncalculated motion that can alter the motion of the c.m., it's an unaccounted for force. When "dark matter" arrived on the scene it was a catch-all for matter we couldn't see. It's only when the explanations for "normal matter hidden from view" fell one-by-one that dark matter took on exotic properties. (In other words, super-smart people have already done the math on hidden galaxies of brown dwarfs and neutron stars being the source of the gravity). I'm betting that if there is a revolutionary simplification to it all, it is because fundamental constants are changing with time. Thus redshift, as ars also speculates, isn't a true measure of velocity. But I understand that super-smart people are doing the measurements on this as well and are finding no changes.
mnw21cam 10y ago
>> Black holes don't exist (time dilation prevents them from forming in a finite time) > It's true that distant observers cannot observe anything past the event horizon. But if you doubt that a black hole exists, you can always dive into it; the black hole will then certainly exist for you, and in a finite time. But because of time dilation, in the meantime, the entire rest of the universe comes to an end. At the very point at which you pass the event horizon, time dilation is infinite, and therefore the universe outside passes by at infinite speed. Therefore, from our outside observation, no matter actually passes through the event horizon. Therefore, a black hole does not consist of a singularity protected by an event horizon, but rather a sphere of density such that time dilation is almost equivalent to infinity throughout. The sphere is prevented from becoming more dense by time dilation itself. Now, I know that the above speculation is completely crackpot (but hopefully reasonably informed crackpot), but I would absolutely love to have a proper black hole expert tell me exactly why it is wrong.
- snarfy 10y ago
  Relativity is about the laws of physics being the same for everyone regardless of reference frame. You are correct that you can never observe the singularity. It will never form within a finite time in any reference frame you can take. Anything falling in will appear stuck as a final ghost/imprint on the surface as time dilation approaches zero. The problem with your argument is you are not taking into account the reference frame inside the black hole. It's still a valid reference frame in relativity even if you can never observe it, so it must be considered. Also, the same theory that is giving you time dilation to make your argument is what predicts black holes, so it's a bit of a circular reasoning.
  - ars 10y ago
    > You are correct that you can never observe the singularity. It will never form within a finite time in any reference frame you can take. So that means there are no black holes in the universe as actual objects - none have formed yet, and none will (in our time). So why does LIGO claim two black holes merged, if black holes can't exist? > The problem with your argument is you are not taking into account the reference frame inside the black hole. It's still a valid reference frame in relativity even if you can never observe it, so it must be considered. Considered from a mathematical point of view, definitely. Considered as an observable object? No. So to consider it: All the other matter that is falling in also time dilated (relative to you) to infinity. So basically you will fall in alone, with nothing accompanying you, and no black hole will form.
ars 10y ago
> you can always dive into it; the black hole will then certainly exist for you, and in a finite time. Will it? All the other matter that is falling in also time dilated (relative to you) to infinity. So basically you will fall in alone, with nothing accompanying you, and no black hole will form. > Consider the Bullet Cluster, which is two colliding galactic clusters. I'm aware of that, but it's not conclusive. Imagine you never heard of dark matter - would that be the first place you jump to? Or would you imagine some very large object emitting hot gas, and moving, and not being slowed by the incoming gas. Such an object could not be seen because of the intensely hot gas between it and us, but the gravity would show up in the gravity map. And there's your "dark", but ordinary, matter. > If this redshift were gravitational, it would imply that our galaxy is at the top of a gravitational potential hill. This means that our place in the universe is very privileged, which is unlikely. When we see a distant "star", it's actually an entire galaxy, or even galaxy cluster. So the gravitational mass of that entire object is redshifting the light, but only our little sun is blueshifting it on the other end. The net result is redshift, as we see it. It's not a coincidence that objects close to us are actually blueshifted.

justifier 10y ago

> Consider the Bullet Cluster, which is two colliding galactic clusters. The gravitational center of mass is offset from the visible center of mass. This offset cannot be explained as potential energy of visible matter. There must be something else, invisible and massive, i.e. dark matter. i'd argue another possible explanation to add to your i.e. was addressed by the gp gp> then galaxies are not moving in the way we currently think they are. the movement of gyroscopes can alter a system's center of mass https://www.youtube.com/watch?v=n_6p-1J551Y https://www.youtube.com/watch?v=n_6p-1J551Y

dhimes 10y ago
The rotation is the gyroscope. And the meaning of your last statement (the movement of gyroscopes) is unclear. The video is cool, but well understood by the same physics that is being applied to the understanding of the galaxies.
- justifier 10y ago
  exactly, but the gp threw in the caveat gp> then galaxies are not moving in the way we currently think they are. so if our calculations already take into account the gyroscopic movement of the bodies within the system, still the gp's thought experiment accounted for this by saying the real nature of the motion of the bodies is different than the motion that we are currently using in our calculations just saying dark matter ignores the potential for other valid explanation for the phenomena instead of there being dm offsetting the center of mass the gyroscopic motion of the bodies within the system also could explain the offset 'not moving in the way we currently think' is a vague statement and could be a direction of rigor for the gp if thae wished to pursue the idea some underlying questions that need to be answered by anyone that suggests our current understanding is incorrect in this regard would need to address: how are they moving differently? how could we detect the difference? how can our incorrect perception be explained? my> the movement of gyroscopes can alter a system's center of mass the cube video was intended to show that yes, this is well understood, and exhibit how changing the nature of the rotation of the gyros: location, direction, speed; in the cube you could move the center of mass to wherever you'd like add another dimension allowing the gyros to move freely stead being fixed within a cube and even more freedom to alter the center of mass could be achieved https://www.youtube.com/watch?v=UnpLEnIqj_A https://www.youtube.com/watch?v=UnpLEnIqj_A i agree it is well understood.. that is why i was using it as naive evidence to defend the gp's thought experiment from being dismissed poorly
  - dhimes 10y ago
    add another dimension allowing the gyros to move freely stead being fixed within a cube and even more freedom to alter the center of mass could be achieved It's the fact that it is fixed within the cube that allows it to move the cm. That only happens because of the reaction force it can exert against the ground. In the absence of external forces the cm won't move (strictly, won't accelerate). In a sense this is a tautology. So it's not an uncalculated motion that can alter the motion of the c.m., it's an unaccounted for force. When "dark matter" arrived on the scene it was a catch-all for matter we couldn't see. It's only when the explanations for "normal matter hidden from view" fell one-by-one that dark matter took on exotic properties. (In other words, super-smart people have already done the math on hidden galaxies of brown dwarfs and neutron stars being the source of the gravity). I'm betting that if there is a revolutionary simplification to it all, it is because fundamental constants are changing with time. Thus redshift, as ars also speculates, isn't a true measure of velocity. But I understand that super-smart people are doing the measurements on this as well and are finding no changes.

mnw21cam 10y ago

>> Black holes don't exist (time dilation prevents them from forming in a finite time) > It's true that distant observers cannot observe anything past the event horizon. But if you doubt that a black hole exists, you can always dive into it; the black hole will then certainly exist for you, and in a finite time. But because of time dilation, in the meantime, the entire rest of the universe comes to an end. At the very point at which you pass the event horizon, time dilation is infinite, and therefore the universe outside passes by at infinite speed. Therefore, from our outside observation, no matter actually passes through the event horizon. Therefore, a black hole does not consist of a singularity protected by an event horizon, but rather a sphere of density such that time dilation is almost equivalent to infinity throughout. The sphere is prevented from becoming more dense by time dilation itself. Now, I know that the above speculation is completely crackpot (but hopefully reasonably informed crackpot), but I would absolutely love to have a proper black hole expert tell me exactly why it is wrong.

snarfy 10y ago
Relativity is about the laws of physics being the same for everyone regardless of reference frame. You are correct that you can never observe the singularity. It will never form within a finite time in any reference frame you can take. Anything falling in will appear stuck as a final ghost/imprint on the surface as time dilation approaches zero. The problem with your argument is you are not taking into account the reference frame inside the black hole. It's still a valid reference frame in relativity even if you can never observe it, so it must be considered. Also, the same theory that is giving you time dilation to make your argument is what predicts black holes, so it's a bit of a circular reasoning.
- ars 10y ago
  > You are correct that you can never observe the singularity. It will never form within a finite time in any reference frame you can take. So that means there are no black holes in the universe as actual objects - none have formed yet, and none will (in our time). So why does LIGO claim two black holes merged, if black holes can't exist? > The problem with your argument is you are not taking into account the reference frame inside the black hole. It's still a valid reference frame in relativity even if you can never observe it, so it must be considered. Considered from a mathematical point of view, definitely. Considered as an observable object? No. So to consider it: All the other matter that is falling in also time dilated (relative to you) to infinity. So basically you will fall in alone, with nothing accompanying you, and no black hole will form.

ars 10y ago

> you can always dive into it; the black hole will then certainly exist for you, and in a finite time. Will it? All the other matter that is falling in also time dilated (relative to you) to infinity. So basically you will fall in alone, with nothing accompanying you, and no black hole will form. > Consider the Bullet Cluster, which is two colliding galactic clusters. I'm aware of that, but it's not conclusive. Imagine you never heard of dark matter - would that be the first place you jump to? Or would you imagine some very large object emitting hot gas, and moving, and not being slowed by the incoming gas. Such an object could not be seen because of the intensely hot gas between it and us, but the gravity would show up in the gravity map. And there's your "dark", but ordinary, matter. > If this redshift were gravitational, it would imply that our galaxy is at the top of a gravitational potential hill. This means that our place in the universe is very privileged, which is unlikely. When we see a distant "star", it's actually an entire galaxy, or even galaxy cluster. So the gravitational mass of that entire object is redshifting the light, but only our little sun is blueshifting it on the other end. The net result is redshift, as we see it. It's not a coincidence that objects close to us are actually blueshifted.