Friday, 7 December 2018

Dark fluid: this bit doesn't make sense

From Space Daily:

The preamble:

Our best theoretical model can only explain 5% of the universe. The remaining 95% is famously [what sort of justification is that?] made up almost entirely of invisible, unknown material dubbed dark energy and dark matter. So even though there are a billion trillion stars in the observable universe, they are actually extremely rare.

The two mysterious dark substances can only be inferred from gravitational effects. Dark matter may be an invisible material, but it exerts a gravitational force on surrounding matter that we can measure. Dark energy is a repulsive force that makes the universe expand at an accelerating rate.

The two have always been treated as separate phenomena. But my new study, published in Astronomy and Astrophysics, suggests they may both be part of the same strange concept - a single, unified "dark fluid" of negative masses.

Jolly good, now here's the logic...

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...

My model shows that the surrounding repulsive force from dark fluid can also hold a galaxy together. The gravity from the positive mass galaxy attracts negative masses from all directions, and as the negative mass fluid comes nearer to the galaxy it in turn exerts a stronger repulsive force onto the galaxy that allows it to spin at higher speeds without flying apart.

That's a poor explanation. How can positive mass attract negative mass, but negative mass repel positive mass? Either the two repel each other (being mirror images)... or the two effects would cancel each other out.
Greater minds than mine reckon that there's no such thing as gravity anyway: space-time is bent by mass and objects travel 'downwards' to where time is passing more slowly (where there is more mass slowing time down). Just like a log which is floating down a river will come to rest in a static pool on the bank of the river if given half the chance.

So negative mass would just have the same effect on matter with negative mass. The logical conclusion would be that matter with positive mass would perceive time as passing more quickly if it were near negative mass, leading to the repulsive effect.

And what if you manage to force negative and positive mass matter together and mix it together, does it then have zero mass?


Sackerson said...

Physics gets weird:

Mark Wadsworth said...

S, superficially yes. But once they've worked it out, the actual explanation is usually quite simple. Something we can all grasp.

paulc156 said...

General Relativity doesn't imply as you state that, "there is no such thing as gravity" rather that gravity is a fictional force. It appears as if were a force and can be considered one for most practical purposes but it is an artefact of curved space time. Not intrinsic or fundamental and plainly not correct at either great distances or in very large gravitational fields.
Hence an object of a certain mass in motion in the vicinity of a more massive object will travel in a straight line, 'along a geodesic'. That is the shortest possible distance on the curved surface of space time. That surface being curved by the mass of both objects. Hence the moon is in fact constantly travelling in a straight line space time. It does depend on initial conditions, like speed and also whether the object is spinning effects the path to a small degree.
Ref the negative mass. These theories are only made coherent by consideration of 3 types of mass. Inertial mass like in Newtons F=ma 2nd law, active gravitational mass (the source of the gravitational field), and passive gravitational mass (mass that is evident from the force produced in a gravitational field). All three have to be equivalent. That is they must satisfy conservation of momentum laws and Einstein's equivalence principle which just states that the acceleration of a massive body due to gravitation is independent of the amount of mass being accelerated. Under these assumptions the negative mass would repel the positive but not vice versa! At least it is mathematically consistent and doesn't contradict Einstein's Field equations. Though I haven't checked that myself! :) That is at least widely accepted. Whether it is the real explanation for dark matter/energy is beyond my ken. It's certainly not a popular explanation for dark matter which is still thought by most cosmologists to be done some form of weakly interacting particle(s) (wimp).

Dinero said...

Energy does not exist independently of the movement of objects that it describes. For example if an Apple is raised it has potential energy, clearly the apple has nothing new itself. The system of the Apple and gravity has the potential for movement potential energy . If the Apple is released it moves towards the ground and just before it lands it has kinetic energy ke=mv2 . A measure of its movement.

Ben Jamin' said...

Gravity is negative energy. Total amount of energy in the universe is zero.

Mark Wadsworth said...

PC, you really are pompous sometimes. First you explain at length what everybody assumes and which I boiled down to one sentence. Then you make a leap of logic and simply restate that +ve mass attracts -ve mass but that -ve mass repels +ve mass on the basis of no further evidence whatsoever.

Din, I like your thinking. But (I think) there is such a thing as energy without mass i.e. first fraction of a second after big bang.

BJ, that sounds vaguely plausible, but I've no idea if it's true.

Robin Smith said...

I go to Reading Astronomical Society monthly, since 1995. They always have top Pro-Am speakers. Last month the topic was similar. I was asking how everything could be accelerating away from everything else like an expanding balloon. "Isn't all the matter actually collapsing into something else under normal gravity?" He said no one really knows it's all just ideas. The best one being another universe of the many was interacting and attracting ours by its own gravity.

It's the sort of language priests used to use in ancient times.

Where you aware in the enlightenment the nouvo scientists where devoutly Christian and trying to find a way to use the new scientific approach to prove that God was real.

Much akin to cosmic science today. Very interestingly in terms of the collective psyche.

Robin Smith said...

Phone typo: were

paulc156 said...

MW. Thanks. And you can be pretty obtuse when you want. So it kind of cancels nicely.

1. You said in your article. "Greater minds than mine reckon that there's no such thing as gravity anyway".
That's wrong. Greater minds don't deny there is gravity, merely that gravity is not a force. Not that it doesn't exist.

2. You whinged that I have made comments regards +mass attracting /...-mass repels "without evidence".
It's a 'theoretical' proposal that is made in the paper you cite, not one based on evidence. There is no evidence and won't be any until and if experimentalists can reproduce the negative mass in a lab and test it.
The ideas presented are contingent. They are inferred mathematically and may have no part in nature. They are plausible 'if' the 3 types of mass satisfy conservation of momentum laws and Einstein's equivalence principle. That may or may not be the case.
If you don't like proposals or comments that aren't backed by hard "evidence"...why invite comments on theoretical physics?

3. You state in response to Din:
"But (I think) there is such a thing as energy without mass i.e. first fraction of a second after big bang."
BEFORE the big bang, not AFTER. After the BB energy has already been converted to matter. That was the bang.

Dinero said...

Energy is not an object it is a measurement of the state of an object, particularly that objects velocity or vibration. Treating a measurement as an object actually has a name, Reification fallacy.

Mark Wadsworth said...

PC, I'd stay off science if I were you.

Din, agreed, for example, temperature is a measure of the average speed at which molecules are moving, and heat transfer is just some molecules moving more slowly and speeding up other molecules. So temperature and heat require there to be some mass there first.

Nonetheless, the way I understand it, there is such a thing as energy in the absence of mass, like photons or electric sparks. You can't capture photons or electric sparks in a bottle, but they clearly exist, you can see them. The big bang started with energy which somehow turned into 'mass'.

paulc156 said...

Electric sparks! Lol. Electrons exchanging photons. Electrons always possess mass.
In any case energy and mass interchangeable ever since 1905. Two sides of same coin. Check Alan Guth inflation theory. Nearly 40 years since he and others explained what banged. Only something with mass can 'bang'. Sorry just can't stand by and see you murder a beloved subject :)

Mark Wadsworth said...

PC, you clearly don't understand the rules of theoretical physics.

paulc156 said...

'Energy without mass' Electric sparks though?! I mean come on you can hardly blame me. ;)

Mark Wadsworth said...

PC "In any case energy and mass interchangeable ever since 1905"

"After the BB energy has already been converted to matter"

One of the rules is you make up your mind what position to take and stick to it. If you had any intellectual honesty you would notice you have contradicted yourself merely in order to contradict somebody else.

Energy can clearly turn into masd and vice versa, but they are not the same at all. Like ice and water.

By your own admission, before the big bang there was only energy and no mass.

Therefore, you can have energy without mass e.g photons, the example I gave above. Again, by your own admission electric sparks are photons.

Dinero said...

Referring to mass rather than an object is a bit of a red herring. The point is to have energy you need an OBJECT. light can transfer the measurable characteristic called energy from source object to destination object but the phenomena called light is not energy. Energy is not an object. The original article refers to energy as a substance , which entails that it is an object. That is wrong , popular science offence of Reification.

Mark Wadsworth said...

Din, the article is nonsense, and I am tempted to agree with your "no energy without mass" rule. It applies to many types of energy (kinetic energy, electric energy) but what about photons? They have no mass but exert a force (that no about those space craft with big silver sails driven by photons).