The Heat Death - Is it survivable?

[Steel]

7 minutes ago, Diche Bach said:

Check out the whole video before you decide

I'm afraid I don't have the time right now, but i'd be very surprised if it says that something other than gravity is the reason that galaxies stay together  

[Diche Bach]

Well correct me if I'm wrong, but gravity is defined in terms of mass. Dark matter cannot be directly observed in the same way that normal matter can--although it can be indirectly observed by gravitational-lensing--and so the "mass" of dark matter (if it has any) also cannot be observed directly. Apparently they have reason to believe that, in very rare instances, dark matter DOES interact with normal matter, but this is apparently so rare an occurrence that the experiments seeking to observe this sort of interaction have been running for years without any detections as yet. Dark matter, otherwise does not interact with the rest of the universe in any way which can be observed.

In the sense that the total gravity which could exist as a result of normal matter is insufficient to account for the behavior of galaxies, and with something ("dark matter") observed to exist as a network of "halos" enveloping the strands of the superclusters in the observable universe, one can conclude that dark matter appears to have mass and thus exerts "gravity," in the same way that normal matter does; but dark matter otherwise does not interact with normal matter, i.e., it also behaves as if it has no mass. To say nothing of the fact that, dark matter's effects do not appear to be moderated by the space between objects in the same way that gravitational forces are moderated.

My take on this is: dark matter does something which appears superficially like gravity, but it may not be gravity, and indeed the fact that its effects on the cosmos defy some of the predicted effects of gravity suggest that what dark matter is doing is not "gravity" in the strictest sense. Of course referring to what it is doing as gravity makes sense for the time being, and in the loose sense that we use the word "gravity" to refer to any attractive force it is as good as any other I suppose. Even laypeople have a notion of what "gravity" is, and without more insights into what dark matter actually is, there is no point in making up a new word to refer to the attractive force "it" exerts in the cosmos. But that does not mean that dark matter operates through gravity; it may or it may not is what I gather.

In sum, the universe is imperfectly understood at present, and thus I remain skeptical that our projections of what it will be doing trillions of years hence are robust. 

Edited September 14, 2016 by Diche Bach

[Steel]

16 minutes ago, Diche Bach said:

Well correct me if I'm wrong, but gravity is defined in terms of mass. Dark matter cannot be directly observed in the same way that normal matter can--although it can be indirectly observed by gravitational-lensing--and so the "mass" of dark matter (if it has any) also cannot be observed directly. Apparently they have reason to believe that, in very rare instances, dark matter DOES interact with normal matter, but this is apparently so rare an occurrence that the experiments seeking to observe this sort of interaction have been running for years without any detections as yet. Dark matter, otherwise does not interact with the rest of the universe in any way which can be observed.

In the sense that the total gravity which could exist as a result of normal matter is insufficient to account for the behavior of galaxies, and with something ("dark matter") observed to exist as a network of "halos" enveloping the strands of the superclusters in the observable universe, one can conclude that dark matter appears to have mass and thus exerts "gravity," in the same way that normal matter does; but dark matter otherwise does not interact with normal matter, i.e., it also behaves as if it has no mass. To say nothing of the fact that, dark matter's effects do not appear to be moderated by the space between objects in the same way that gravitational forces are moderated.

My take on this is: dark matter does something which appears superficially like gravity, but it may not be gravity, and indeed the fact that its effects on the cosmos defy some of the predicted effects of gravity suggest that what dark matter is doing is not "gravity" in the strictest sense. Of course referring to what it is doing as gravity makes sense for the time being, and in the loose sense that we use the word "gravity" to refer to any attractive force it is as good as any other I suppose. Even laypeople have a notion of what "gravity" is, and without more insights into what dark matter actually is, there is no point in making up a new word to refer to the attractive force "it" exerts in the cosmos. But that does not mean that dark matter operates through gravity; it may or it may not is what I gather.

In sum, the universe is imperfectly understood at present, and thus I remain skeptical that our projections of what it will be doing trillions of years hence are robust. 

You are almost right when you say that dark matter doesn't appear to interact with ordinary matter. It doesn't interact, EXCEPT via gravitational interactions. The dark matter gravitational lensing you mention corroborates this. If we decide not to think about gravity in a Newtonian way (i.e a force) and think of it instead as the effect of mass warping space-time, then the dark matter lensing observed can only really be explained (at least without creating a dramatically new model of the universe) by the dark matter having conventional mass.

AFAIK, almost all current cosmological models consider dark matter to interact gravitationally.

 

[Diche Bach]

2 minutes ago, Steel said:

You are almost right when you say that dark matter doesn't appear to interact with ordinary matter. It doesn't interact, EXCEPT via gravitational interactions. The dark matter gravitational lensing you mention corroborates this. If we decide not to think about gravity in a Newtonian way (i.e a force) and think of it instead as the effect of mass warping space-time, then the dark matter lensing observed can only really be explained (at least without creating a dramatically new model of the universe) by the dark matter having conventional mass.

AFAIK, almost all current cosmological models consider dark matter to interact gravitationally.

 

Well then why does distance not seem to matter to dark matter? What it does is obviously analogous to gravity, But given it may lack one of the fundamental characteristics that is required for gravity (mass) it seems presumptive to me to conclude that what it is doing is exactly the same thing as gravity, i.e., the attractive force observed between normal matter and depending on mass and distance between objects. I believe I have read some scholars who make a point of NOT referring to the effects of dark matter as gravity, but instead as the "attractive force" or some such.

Anyway, not trying to be argumentative, merely discussative

I am certainly no expert and welcome being instructed by those who know better.

[Steel]

3 minutes ago, Diche Bach said:

Well then why does distance not seem to matter to dark matter? What it does is obviously analogous to gravity, But given it may lack one of the fundamental characteristics that is required for gravity (mass) it seems presumptive to me to conclude that what it is doing is exactly the same thing as gravity, i.e., the attractive force observed between normal matter and depending on mass and distance between objects. I believe I have read some scholars who make a point of NOT referring to the effects of dark matter as gravity, but instead as the "attractive force" or some such.

Anyway, not trying to be argumentative, merely discussative

I am certainly no expert and welcome being instructed by those who know better.

I've never heard of distance not affecting dark matter, could you point in the direction of some reading?

[Diche Bach]

I'm afraid I cannot point you to any specific reading in which the subject of "distance not affecting dark matter" is addressed.

However . . . consider this: where "is" dark matter? Is it everywhere? Is it nowhere? Does it move? Is it fixed in space time?

I get that it can be inferred to exist in a halo around galaxies and larger structures by the observed bending of radiation from objects farther away. But that doesn't necessarily mean that dark matter only exists in those places does it, or that it is evenly distributed throughout the internal space of the normal matter it seems to surround, does it? It may or it may not have discrete boundaries in the way that observable matter does. It may be everywhere, it may be nowhere (in the sense that it is neither matter nor energy but something we have yet to fully comprehend).

In order to calculate the distance between two points, one must be able to determine where those two points are, and it seems to me that the current models of "dark matter" are not nearly that precise. So the degree to which the attractive force of a "particle" of dark matter (or clump, halo, cloud, field, web, scaffold, whatever) is or is not moderated by the distance between it and either other dark matter or normal matter is not a topic of inquiry, and thus it wouldn't surprise me in the least if there are no scholars concerned with the question. But that doesn't settle the question I think.

In order to address the question of whether distance matters to dark matter, one must first know where dark matter is, and if it exists in discrete packages interspersed with boundaries of "no dark matter here," where dark matter is NOT. It seems to me they are not yet in a position to consider the phenomena they call "dark matter" in this way, thus my reference to it as a "deus ex machina" in a preceding post. 

The attractive effects of dark matter may be just as subject to distance as normal matter, or they may not be. Without knowing where it is and is not, and if it is in fact NOT everywhere, they are in no position to address the question I suspect.

[Steel]

20 hours ago, Diche Bach said:

I'm afraid I cannot point you to any specific reading in which the subject of "distance not affecting dark matter" is addressed.

However . . . consider this: where "is" dark matter? Is it everywhere? Is it nowhere? Does it move? Is it fixed in space time?

I get that it can be inferred to exist in a halo around galaxies and larger structures by the observed bending of radiation from objects farther away. But that doesn't necessarily mean that dark matter only exists in those places does it, or that it is evenly distributed throughout the internal space of the normal matter it seems to surround, does it? It may or it may not have discrete boundaries in the way that observable matter does. It may be everywhere, it may be nowhere (in the sense that it is neither matter nor energy but something we have yet to fully comprehend).

In order to calculate the distance between two points, one must be able to determine where those two points are, and it seems to me that the current models of "dark matter" are not nearly that precise. So the degree to which the attractive force of a "particle" of dark matter (or clump, halo, cloud, field, web, scaffold, whatever) is or is not moderated by the distance between it and either other dark matter or normal matter is not a topic of inquiry, and thus it wouldn't surprise me in the least if there are no scholars concerned with the question. But that doesn't settle the question I think.

In order to address the question of whether distance matters to dark matter, one must first know where dark matter is, and if it exists in discrete packages interspersed with boundaries of "no dark matter here," where dark matter is NOT. It seems to me they are not yet in a position to consider the phenomena they call "dark matter" in this way, thus my reference to it as a "deus ex machina" in a preceding post. 

The attractive effects of dark matter may be just as subject to distance as normal matter, or they may not be. Without knowing where it is and is not, and if it is in fact NOT everywhere, they are in no position to address the question I suspect.

I see where you're coming from.

Granted we don't know enough about it's make-up to know many things about it, but the one thing we do know with at least some degree of certainty is that what we call "dark matter" appears to have mass and thus interacts gravitationally with what we call "normal matter". From this we can infer "where" this dark matter is concentrated by looking for it's gravitational signatures i.e. gravitational lensing, galaxy rotation curves and so on. 

So long as we have evidence that this is in fact a gravitational attraction (which almost all observational evidence does point to AFAIK) and not some other unknown force (which I would find surprising considering how close the properties of the observed effects are to gravity), then we can actually reasonably localise, with an error, dark matter clusters (clumps, regions of high concentration, whatever your chosen phrase).

[Diche Bach]

True. It probably is "gravity." But it might not be, and given it doesn't seem to have "mass" in the same way that normal matter does, that has to be kept in mind. That is all I'm saying.

If one assumes that one's current paradigms are perfect and sufficient to explain all that there is to know, then avenues which could shed light on new paradigms might be stifled. This is certainly something Lee Smolin has argued with respect to String Theory.

 

[Steel]

11 hours ago, Diche Bach said:

True. It probably is "gravity." But it might not be, and given it doesn't seem to have "mass" in the same way that normal matter does, that has to be kept in mind. That is all I'm saying.

If one assumes that one's current paradigms are perfect and sufficient to explain all that there is to know, then avenues which could shed light on new paradigms might be stifled. This is certainly something Lee Smolin has argued with respect to String Theory.

We've seen nothing observationally AFAIK that suggests that dark matter does not have mass in the same way normal matter does. 

I totally agree that it's very dangerous to assume that your current paradigs will be sufficient to explain everything. Equally I think there's no need try to overcomplicate things (which is a big problem in many areas of theoretical physics) by creating new theories and paradigms to explain anything unknown before we've ruled out current ones.