'Dark fluid' with negative mass could dominate the universe • Hacker News Board

Re: 'Dark fluid' with negative mass could dominate the universe

#181

Post by therein » Thu, Dec 06, 2018, 1:48 AM UTC

deathanatos wrote: post #77

therein wrote: post #38

Earlier quoted context omitted.

Beware the Physical Chem, my son! The laws that arn’t, the constants that vary. Beware the phlogiston, my little one And of the molality be wary. He took his entropy in hand Long time the adiabatic foe he sought So rested he by the delta T And stood awhile in thought. And as in Newtonian Thought he stood The Physical Chem with Beer’s Law Plot, Came Bohring through the orbital wood And took quantum leaps when hot! PV!…

If by recognize you mean that it's a variation/remix of "Jabberwocky"[1], then yes. The second corresponding verse (so this corresponds to "He took his entropy in hand"), so others can see the resemblance (I chose the second since the first is a bit harder to see): He took his vorpal sword in hand: Long time the manxome foe he sought— So rested he by the Tumtum tree, And stood awhile in thought. [1]: https://en.wikip…

Very cool. Today I learned something about a AXE (Alpha Chi Epsilon chemistry fraternity).

Re: 'Dark fluid' with negative mass could dominate the universe

#182

Post by btilly » Thu, Dec 06, 2018, 1:49 AM UTC

millstone wrote: post #171

thaumasiotes wrote: post #155

Earlier quoted context omitted.

So, electrons are attracted to protons by the electromagnetic force, but they don't make it all the way there because they are repelled by some other force. You don't have a paradox because our model of the electromagnetic force doesn't specify that it's the only force there is. But if a negative mass is moving towards you and encounters a repulsive force, that repulsive force will, by definition, move the negative m…

> they don't make it all the way there because they are repelled by some other force A repulsive force is not the best way to think about it. The potential of the nucleus is the usual -1/r, and goes to (negative) infinity at zero. A repulsive force would be incorporated into the potential and appear as a bump around the nucleus, and would mess up the electron orbital. A hand-wavy explanation of why the electron doesn…

A different hand-wavy explanation. The places that an electron can be found are described by a wave pattern. If the electron is staying in place around a nucleus, that wave pattern has to be a standing wave that reinforces itself. To reinforce itself it has to wrap around the nucleus an integer number of times.

This explanation doesn't just explain why it doesn't fall in, it also explains why there are discrete shells that it could be found in, corresponding to how many times it wraps around the nucleus. (It doesn't explain why only a finite number can fit in each shell though. Or why bigger shells can have more electron orbitals. Or...well the actual theory has to be good for something!)

Re: 'Dark fluid' with negative mass could dominate the universe

#183

Post by privong » Thu, Dec 06, 2018, 1:57 AM UTC

ars wrote: post #168

privong wrote: post #103

Earlier quoted context omitted.

> That assumes that inertial mass = gravitational mass, which is assumed to be true, not not proven. The assertion has been tested experimentally. Inertial and gravitational mass are seen to be equivalent within the bounds of experimental accuracy. The wikipedia article on the "Equivalence Principle" has lists of tests for various versions of the principle: https://en.wikipedia.org/wiki/Equivalence_principle#Modern_u…

And the negative mass postulated here? We don't know if it's still equivalent there because we have never tested it. It would be a lot simpler if inertial mass was negative gravitational mass in this theory. Then you have repulsive gravity with normal behavior under force.

I see I misunderstood that you were specifically questioning the equivalence for this postulated negative mass. I thought your statement was a more general one.

Re: 'Dark fluid' with negative mass could dominate the universe

#184

Post by krapp » Thu, Dec 06, 2018, 2:14 AM UTC

gradys wrote: post #51

NedIsakoff wrote: post #36

Here comes the Alcubierre Warp Drive!

Exactly where my mind went. Does the perspective described in the paper make the Alcubierre drive seem more plausible? Or is there something about the nature of the dark fluid hypothesized that would make it useless for something like that?

>Or is there something about the nature of the dark fluid hypothesized that would make it useless for something like that?

Assuming it was, literally, some kind of magical FTL juice... it all seems to be outside the galaxy, which means tens of thousands of years' travel just to get to it. If we're willing and able to do that, why bother with FTL at all?

Re: 'Dark fluid' with negative mass could dominate the universe

#185

Post by marcosdumay » Thu, Dec 06, 2018, 2:23 AM UTC

starbeast wrote: post #113

marcosdumay wrote: post #108

Earlier quoted context omitted.

> Or do I have that wrong and photons merely follow the distortions and not cause any of their own? You have that wrong in the momentum of massless particle has mass, independently of its carrier. Massless particles do not actually exist, what exist are particles with zero "mass at rest" and that are never at rest.

Ahh, I was getting a bit confused from photons distorting spacetime off their wavelength and plank's constant, given they also apparently have no mass. Thanks for that. I have to go and re-read a lot of stuff now though. ;)

You may like to make a quick read of this:

https://en.wikipedia.org/wiki/Energy%E2%80%93momentum_relati...

Besides it being a basic relation for relativity, there's also an entire "parallel" quantum mechanics for particles that have too much energy at the momentum component based on it.

Re: 'Dark fluid' with negative mass could dominate the universe

#186

Post by jon_richards » Thu, Dec 06, 2018, 2:37 AM UTC

skykooler wrote: post #74

mklauber1 wrote: post #14

Earlier quoted context omitted.

I think what they're saying is that positive mass galaxies attract the negative mass, even as the negative mass repels the positive mass (and all other negative mass). In a stationary system, eventually the two will reach an equilibrium. However, the effects of this in a system in which the positive mass galaxy is spinning is that the negative mass counteracts the forces of inertia, allowing the galaxy to spin at hig…

Wouldn't that allow for a "perpetual motion" setup where a blob of normal mass is in front of a blob of negative mass? The negative mass would push the positive mass forward, and then be attracted to it and follow. What am I misunderstanding?

It would be perpetual motion, but momentum and energy would remain the same. Both depend on mass (so negative mass accelerating creates negative momentum and energy).

Re: 'Dark fluid' with negative mass could dominate the universe

#187

Post by jon_richards » Thu, Dec 06, 2018, 2:57 AM UTC

walrus1066 wrote: post #129

Pxtl wrote: post #42

Would this be only gravitational mass that's negative or would it be both gravitational mass and inertial mass? Because negative inertial mass is zany and wierds me out. Negative gravitational mass behaves in a way that makes sense to me.

Has to be gravitational only. Otherwise positive mass is repelled from negative mass, but the negative mass accelerates towards it. So both masses accelerate in the same direction, until they have infinite kinetic energy! Conservation of energy & momentum would still hold, because negative mass would have negative energy & momentum, cancelling out that of the positive mass. But the above surely would be an 'unphysica…

>Negative masses are a hypothetical form of matter that would have a type of negative gravity – repelling all other material around them. Unlike familiar positive mass matter, if a negative mass was pushed, it would accelerate towards you rather than away from you.

Pretty sure the author means both.

A continuously accelerating system seems "unphysical", but we have an example already: the accelerating expansion of the universe.

Re: 'Dark fluid' with negative mass could dominate the universe

#188

Post by jon_richards » Thu, Dec 06, 2018, 3:01 AM UTC

tylerjwilk00 wrote: post #109

sixo wrote: post #55

Earlier quoted context omitted.

This is explicitly very different from that. There's no claim of "negative mass dark matter particles" in _ever_ location, rather, they have a specific distribution.

That distribution being all the places that aren't normal matter particles. So primarily outside of galaxies.

No. The negative mass matter clusters around galaxies because it accelerates towards positive mass and away from other negative mass. The area between galaxies becomes largely empty in the simulations.

Re: 'Dark fluid' with negative mass could dominate the universe

#189

Post by vtesucks » Thu, Dec 06, 2018, 3:06 AM UTC

Alright question for all you genius physicists- what makes you visit this forum which is primarily a discussion board for news and startups (primarily)in the field of Information Technology? I'm curious because I don't know you're your domain intersects with this forum's.

Re: 'Dark fluid' with negative mass could dominate the universe

#190

Post by DoctorOetker » Thu, Dec 06, 2018, 3:10 AM UTC

dragonbonheur wrote: post #72

Looks like the rest of the world is about to catch up with Jean-Pierre Petit's theories about negative masses surrounding positive mass objects like galaxies and holding them together... Even the proposal for the modification of Einstein's theories... Times are a'changin. It took almost ten years (2007-2017) from JPP being shunned by the scientific community (and the highly politicised French Wikipedia) to others "di…

figure 1 of that paper is virtually identical to the galaxy rotation curve of the current paper! both were N body simulations

thanks for pointing out this earlier work