Will We Ever Know What Dark Matter Is?

The fundamental question is: what's the most basic truths that we can ever know?

If there are hyperdimensional branes the likelihood is that we wont be able to learn much about their origins because of their relationship to our universe. An acceptable answer then becomes "We can't know how they exist..."

On the other hand, if we only make up 15% of the known mass of the universe, that's room enough for 5 more parallel shadow universes living beside us!

Or maybe dark matter just doesn't need as much mass for intelligent life to develop. Who says they need stars and planets?

There is a limit to the changes in the momentum of cold dark matter before it produces visible effects in galaxies of different ages. Explosive processes in the dark matter sector must be rare, whatever their mechanism and whatever their daughter products (even if it quickly decays to cold dark matter again, but on a different trajectory).

> Gravity decreases in proportion to distance squared between objects, but its not observed beyond a certain distance.

-- not to the question of what detailed properties gravitation possesses.

You could infer its existence from indirect effects, but it would be extremely tricky.

First, to transport a qubit, you need to send an entangled particle first. This is usually done with fiber optics. You could also send a bunch of particles in traps on a truck, or over the, air, whatever, but you still need to exchange particles for quantum teleportation. Once you've exchanged entangled particles, you can use them to transmit the quantum state of another particle. This might be useful for quantum encryption, but you could just use the originally exchanged particles instead.

Second, you've already stated this, you cannot transmit classical bits. You'd still need all the original Internet infrastructure to transmit classical information. Things like, the British are coming, a funny cat gif, any message really. In fact, entangled states are actually useless without transmitting classical information about the partner particle. Without that, it's impossible to even detect that the particle is part of an entangled pair, much less use the information for anything. The quantum eraser experiment is a great example of this. Without the information about the other entangled particle, all you get is a screen showing that the particle always went through a single slit. Once you know the which way information about each particle, you can separate them out into two interference patterns that cancel out.

Now, there may be something that connects particles quantumly that can be used for communication. Such a thing is not currently part of quantum mechanics and isn't quantum entanglement, such an effect would need some new name.

Regular matter clumps together to form gas clouds, stars, black holes, planets, etc. In general, matter collapses. This happens because particle interactions and collisions generate heat that gets radiated away. Without a mechanism to lose energy, gravitational collapse isn't possible. When we look at galaxies, the stars, gas clouds, etc, tend to fall inward as they lose energy and more matter gets towards the middle than the outside. In spiral galaxies, you see a huge bulge of stars towards the middle. When we look at how fast they rotate, we measure that matter is distributed more or less evenly across the entire plane of the disk. This measurement is really what kicked off our current understanding of dark matter followed by many other discoveries regarding matter distribution.

If dark matter formed stars, planets, gas clouds, etc, like normal matter, it would clump towards the center of galaxies, just like normal matter.

https://en.wikipedia.org/wiki/Galaxy_rotation_curve

Anyone can theorize whatever they want about the universe, and should not be discourage from doing so. But if your theory makes claims based on current understanding and observations, but the knowledge of that current understanding and observation is incorrect, it seems logical to help that person along. If you want to base your new theories on what is currently understood, it will benefit you greatly to learn as much about current understanding as possible.

You're attempting to write a super-duper machine learning giant app without having bothered previously to even learn how to code. Start by learning how to turn on the computer first, and go from there.

It's easy to kick back and dream about grand theories. It's also easy to forget the steep road of learning that would allow you to even approach that realm.

This depends on how you look at it.

In the standard cosmology we define a preferred frame wherein an observer will see the matter (that's in the most general sense of "not the gravitational field", so it includes atoms and their components, photons, and various types of dark matter (e.g. neutrinos, which are "hot" dark matter, since they move relativistically and do not experience electromagnetism)) content of the universe as homogeneous and isotropic. This is physically reasonable since along every unobscured line of sight we see a lot of galaxies of various shapes, "tilts", sizes, surface brightnesses, and spectral lines. Observations also lead us to conclude that there is a relationship between redshifting of the spectral lines of common types of galaxies (and common radiative occurrences within them, like type A supernovas), and the change of the other observables (angular size on the sky, luminosity, etc.) that correlate with greater distance. This in turn led to the discovery of the Hubble "constant", and provoked ever deeper field telescopic studies to prove its value.

So if we assume that along every line of sight, including obscured ones, we have much the same view of many many galaxies at a variety of distances, we can make a variation on the Friedmann equation that parameterize several things that would lead to the observables of galaxies when we model their known (and unknown) components as a set of perfect fluids.

We can take the Hubble "constant" and put it into a Robertson-Walker vacuum spacetime. RW spacetimes can be grokked by dimensional reduction. Consider a cylinder that we slice (foliate) along its axis into a set of infinitesimally thin circles stacked on top of each other. We describe the radius of each circle with a function r(h) where h is the height of the circle from the base of the cylinder. Where r(h) is constant, we have a cylinder, but if r(h) increases with h, then we have something like a cone balancing on its apex; r(h) can describe a wide variety of shapes. For an 3+1 RW spacetime that is similar to our universe, we foliate on the timelike axis and define a function a(t) where t_0 == now with the spacelike coordinates set on a chosen observer (us here on Earth, for example). "t" counts upwards as we go into the past from t_0, and a(t) goes to zero as t increases. "t" is the lookback time and a(t) is the scale factor. The chosen observer is the special observer mentioned above, who sees the matter of the universe as isotropic and homogeneous at the largest scales. The most useful coordinates on such a spacetime are comoving, that is each gravitationally bound galaxy cluster stays at the same coordinates at every time t.

If we mix together the Friedmann equations, the Lemaître idea of spacetime having a zero radius at some large lookback time, and the RW spacetime that can model that, we get the FLRW model of the standard cosmology. We take the RW case where there is no extrinsic curvature, that is, when we foliate on the timelike axis each spacelike hypersurface is spatially flat; that is similar to saying that when we slice up our dimensionally reduced solid along its height, we get a set of circles of the same radius (i.e. a cylinder rather than a cone). We absorb the expansion parameter into a(t) as another of the fluids.

We then consider two types of fluid: those that dilute away as t -> t_0 -> future and those that do not dilute away. The former is "matter", including dark matter; the latter is "dark energy".

When we consider them as components of an action, diluting-away fluids are attractive and non-diluting fluids are repuslive. When we consider them in terms of the matter tensor T in General Relativity, the diluting-away fluids have positive pressure and the non-diluting fluids have negative pressure.

It's important to return to the point that this model has a preferred frame, and that translating the non-diluting fluid into "the same for all observers in all frames of reference" physics leads one to assume that dark energy is just a feature of the Lorentz-invariant vacuum. So dark energy arises in the cosmological model but corresponds to the ground state of the empty-of-matter spacetime in frames of reference other than the preferred one picked out by the cosmological model.

That is, the statement that "dark energy drives the expansion (via negative pressure or repulsion)" is frame-dependent, and thus observer-dependent, and with a change of frames of reference (and even a change of coordinates on the preferred frame), the statement becomes untrue. What is true in all frames is that there is an intrinsic property of space in an expanding spacetime that has a constant energy-density no matter how large a volume of space is considered.

The exact equation of state of dark energy is an area of active research and also tests to make sure that the assumptions that inevitably lead to it (isotropy at huge scales, homogeneity, spatial flatness, redshift-distance relations and other things implying expansion) are not blown up by evidence from ever finer observations.

So it's not so much a 'label' as a phenomenon whose microscopic details have yet to be discovered.

There are lots of those in physics, and we've had a good century of probing the microscopic details of phenomena discovered at the end of the 19th century and since, so this shouldn't really be causing anyone sleepless nights.

[1] https://en.wikipedia.org/wiki/Neptune

You're pairing space and matter, then time and energy, and comparing them as though these entities are naturally paired in current theory. They aren't. Space and time are elements of spacetime, matter and energy are interchangeable by way of a rather well-known equation, but these things don't arrange themselves as you're trying to do.

> And as for your last sentence, trust me I understand the scientific method, and how proof, evidence, and fact interrelate with knowledge.

So you didn't say, "So many non-scientists think dark matter is proven. It isn't. It's nothing but pure conjecture."

Nothing is ever proven in science (falsified, yes, proven, no). And dark matter and dark energy are both more than "pure conjecture," a domain reserved to notions lacking observational evidence.

Come on. Is it so hard to say "Oops I mixed them up"?

Though the new tab approach still works.

And upon retesting, I see the same, sometimes. But sometimes, there are just a few extra nautil.us lines.

And for sure, opening a new tab is the safe bet.

You can certainly describe gravitation using a massless spin-2 graviton, and perturbative quantum gravity -- another specific quantum field theory -- does exactly that, and is a perfectly fine effective field theory that entirely matches General Relativity absent superposed sources and outside of strong gravity (which is defined by the EFT's renormalization group flow).

You can add this graviton to a particle zoo. But then it's not the particle zoo of the Standard Model, any more than writing down an "action of everything"[1] gives the action of the Standard Model.

> The general laymans meaning of "Standard Model" means everything in physics that is referenced on that chart (including gravity), and that's how I meant it.

is only correct if you underline the "how I [mean] it" part and make that central to evaluating the sentence's truth. It's hard to disprove solipsistic physics, though, and rarely interesting.

Additionally,

> which relate to the 4 fundamental forces (carriers) ... I'm sure you're familiar with this chart.

Sure, but there are several such charts, and they're not all the same. Here's one from Fermilab and SLAC, institutions that are pretty familiar with the Standard Model: http://www.symmetrymagazine.org/standard-model/ (There's no graviton in it).

Fundamental forces come from fundamental interactions, but there is no force police force enforcing a law that there are four of them or that the carriers are gauge bosons in a particle zoo. The Higgs interaction can be treated as a force[2] and its mediator is a scalar boson rather than a gauge boson, so does the Standard Model have four fundamental forces? One can take differing views of the electroweak interaction above 80-90 GeV: does the Standard Model have only two fundamental forces?

One can certainly treat Einstein gravity as at least a d'Alembert force arising from the affine connection; but alternatively one could take the position that d'Alembert forces generically depend on a choice of frame of reference and on that basis they cannot be fundamental. Is gravity a force? You get a different answer from Newton (yes) than you do from either Einstein (yes, but it's fictitious) or Misner, Thorne & Wheeler (mu, there is only spacetime geometry).

So an argument that as there are four fundamental forces there must be four force carriers is on shaky ground to start with. Even if we were to accept that, it does not follow that all the forces in question relate to the local symmetries of the Standard Model.

[1] For example, Carroll's "core theory" here: http://www.preposterousuniverse.com/blog/wp-content/uploads/...

[2] as discussed at last year's Moriond EW, for example, the Higgs force can be measured using atomic spectroscopy: https://indico.in2p3.fr/event/12279/session/7/contribution/1...

There's a willful ignorance in this sentence that belies your youth and intelligence. I suspect you don't have an adequate background to understand the observational evidence for our expectation of dark matter (I barely do to be quite honest). I don't think you can fairly dismiss offhand the conclusions drawn by hundreds of expert physicists based on your experience.

I've known more than one physicist that were also well-studied students of philosophy. If you have reached a brilliant and well-justified conclusion that they failed to see you should clearly write it to justify your case.

>"The only criteria for establishing a scientific truth is still a replicable experiment which proves an implementation according to some established law. Any simulation does not account for such kind of experiment, being mere a "cartoon" made according to some abstract model. The difference between experiment and simulation is of the same kind as between a cartoon and actual reality."

Science (and philosophy for that matter) are defined from consistency of observation. I fail to see your point about an experiment measuring a "cartoon" when that is the reality in which we intrinsically exist and for which prediction will provide the most value.