Fascinating. So this MOND theory works in this case. If I understand correctly, scientists still prefer the dark matter theory because it applies in more cases at galactic scale, and this is just one occurrence of the MOND theory working fine?
The biggest piece of evidence for DM is the BAO patterns in the CMB. Forget all the other numerous mountains of evidence, that is the biggest one. MOND has no good explanation for this without introducing something that's effectively DM.
DM can't explain renzo's rule, or the tully-fisher relationship, or why the milky way has a keplerian return (efe from the magellanic clouds), or why elliptical and lenticular galaxies don't seem to have dark matter. All these are explainable by MOND.
MOND also predicted early galaxies, and a group seeking to disprove MOND by disproving EFE changed their mind because they found evidence of EFE.
> it fits the data best.
It's easy to fit the data when you can conjure a parameter to explain anything. What if I told you that GR is wrong and there's a ball of dark matter orbiting the sun that distorts Mercury's orbit.
Not the same. MOND adds a parameter - the non-newtonianness which is purely a function of the masses and the distances. DM lets you add a new parameter (the DM density) at each point in space. That's effectively an infinite number of parameters, whereas MOND has very few.
> DM lets you add a new parameter (the DM density) at each point in space. That's effectively an infinite number of parameters, whereas MOND has very few.
No one is doing that, though. What cosmologists do is parameterize the statistics of the DM distribution. That's one or two parameters. Then we compare observations to simulations to determine how likely the observed distribution is given the statistical properties. For example, a few galaxies with almost no dark matter would be expected due to the dynamics of clusters and galaxies. You could in principle calculate how often that should be the case, and if we were to observe it much more often than we should then there would be a problem with DM. No one is suggesting that the DM distribution can assume any arbitrary shape.
That's at the universe-sized level. At the galaxy level, as you state, we say "oh, that galaxy has almost no dark matter". That's a per-galaxy parameter. At the Bullet Cluster, we say "the dark matter must be here and here". That's a point-by-point distribution.
No, variation in galaxy properties is an output, not an input, of the model.
You could decide to quantify and catalog different galaxies with one or more parameters that describe their properties. You could then compare whether that catalog is statistically consistent with the output of the model (and must take into account all uncertainties in the model and the observations).
By analogy, you can measure that different people have different heights, but it does not mean that the specific height of each individual person is a unique input parameter in any fundamental model of biology.
Let me change your analogy. You take each person, and measure their height. You also "measure" how tall they "should be". You then show that the differences between their actual height and the height they should have had fits a model. That's nice, but for each person, you still assigned a value for the difference between how tall they are and how tall they should have been.
That's what I mean by "it's a per-galaxy parameter". For each galaxy, to explain the behavior of that galaxy, you're saying "it must have X amount of dark matter".
There is no DNA for galaxies, so how could you know what the properties of a particular galaxy "should be"?
The focus on "per-galaxy parameters" is like expecting to be able to predict how tall Tom Cruise should be after reading a textbook on the theory of evolution.
I wouldn't have to prove you wrong. If your stance is that Mercury's perihelion shift is explained by DM, then I'll counter that GR explains that, gravitational lensing, gravitational waves, black holes, the CMB, the helium abundance, and then some. By Occam's razor, GR would be the preferable theory.
The claim that DM requires conjuring up parameters is completely baseless. There are one or two parameters (besides a handful other parameters from LambdaCDM) that determine the statistics of the DM distribution, and observations match well with simulations based on those parameters. There are small deviations called the dwarf galaxy problem and no one is inventing parameters to explain those, so what are you talking about?
2. whatever it does, you add just enough dark matter to account for that behaviour.
Such process seems fishy, because it can explain ANY observation.
If we would go back 130 years ago where GM was not a thing yet, and GM would be competing with DM theory, occams razor would point to DM, because it is simpler one - it fits with newton nicely.
(not an expert though, just repeating stuff I heard on youtube; I’m happy that experts work on all kinds of angles)
Those are measurements, not parameters. Just like the exact baryonic matter distribution is not a parameter of GR. You have an initial matter distribution, which is a random sample of a probability distribution (that is a part of the model) and then it starts clumping together over time.
You're wrong. They are parameters if you're using them to bestfit another value (rotation curves). This is basic high school science/stats.
And yes, baryonic distribution is absolutely a parameter, but it's not a free parameter (or it's a less free parameter) because it's value is constrained to a measurement that is orthogonal to the quantity inferred (light vs rotation curve). Meanwhile, dm density is a free parameter. It could be zero, or, 10x the baryonic mass, or anything in between.
They're not measurements. The measurements are rotation rates at various distances from the galactic center, then you plug that into a model and the model tells you where the DM is in that galaxy, then you say "DM explains it all for this galaxy!", but no, the amount and distribution of the DM is an output of the model and that cannot prove anything. There is never an explanation for why DM amounts and distribution vary so much. DM theory needs to make predictions we can then test, not produce model outputs.
What you are calling a model is simply a way of quantifying a measurement of a galaxy to describe (or model) its mass distribution. There is no physics involved.
> "DM theory needs to make predictions we can then test"
That is what scientists do: Start from the hypothesis of a dark matter dominated universe, from the beginning (or soon after the big bang), then turn on time and physics (gravity plus gas physics in a computer simulation), and galaxies form as gravity causes matter to clump together. The properties of those theoretical galaxies are testable predictions.
If you were to create any model of the universe, you would require it to have the correct (observed) percentage of galaxies without dark matter, right?
You assert that it is impossible for a model of a dark matter dominated universe to "predict" galaxies without dark matter, but that is exactly what people are looking at here in a large scale cosmological simulation:
https://arxiv.org/abs/2202.05836
> then I'll counter that GR explains that, gravitational lensing, gravitational waves, black holes,
That interpretation of GR assumes that Mercury isnt perturbed by some form of dark matter. Go back and redo all the equations with a dark matter that obeys the right rules before claiming that GR is a better explanation.
The DM distribution itself is effectively a huge number of parameters. You have to have just the right amount of dark matter distributed differently in each case to explain observations and get those best fits.
Yes, the cuspy halo problem wouldn't be a problem at all if you were to simply adjust the infinite parameters that you suggest that DM has. The fact that there are statistical discrepancies proves my point that no one is adjusting a huge number of parameters.
And they still fail to explain other observations which require additional arguments as to why the dark matter is once again distributed in just the right way to give the rotation curve... that is already successfully predicted by MOND in most cases with just one universal parameter.
We have found galaxies with differing amounts of dark matter (as measurer by rotational speed) and have confirmed these measurements with gravitational lensing being more or less effective.
First, most modern research in physics (especially experimental physics) have a ton of coauthors; we’re well past the stage of things being named for a single person.
Second, what makes you think there isn’t great fame in disproving dark matter?
The last person who figured out we were doing incomplete math is the single most famous scientist in the history of the world. Being the next one isn't more exciting than getting some particle named after yourself?
Yeah I interpreted that person’s post as saying “we’ve been doing incomplete math this whole time” is way more exciting, which I completely agree with.
Doing all the work and taking all the stress only to have the EU remove a chance of growth and exit is a problem that I never want to have. I went through some failed startups, and at least that was our own fault, but still I never want to do that again. I don't know what I'd do in this situation.
Because speculative startups require a lot of investment/venture capital, but the VCs need a defined return at some point. They need an exit with a sale, an acquisition or an IPO in order for the whole process to make financial sense. If companies just 'grow' but never sell out, there's not enough return for VCs, so they don't invest. No investment = way less startups to begin with
Especially important if you want to compete in training base models - if they were using 1500 H100s like the quote somewhere above implies, the market rate for that right now is something like $7500-$10k per hour (retail, on demand, so probably lower in reality, but still, it adds up incredibly quickly if you’re training 24 hours per day).
But founders and employees at some point want to leave and do other things. They want to take their stake in the company and sell it to buy a house or retire or pay for their kids' college or whatever.
That requires an exit, either as an acquisition or an IPO.
(In theory, dividends or profit distributions are an alternative, but they're much harder to do anything with because they're mostly in the future and not guaranteed. You can't pay for your kids' college with future profit-sharing that may or may not materialize. And, dividends or profit distributions are the opposite of growth, because you're no longer re-investing in the company.)
Few million dollars split by how many people? A small startup that provided a decent exit for me was sold for 50M EUR. I got 100K from that - the company had over 1000 shareholders. That's not really life changing amount of money, was barely enough to get a mortgage for my small apartment (30% of the price).
BTW the company was failing. If we didn't sell we'd have 0 very soon. It's really not as easy as "well let's just grow I guess".
Because sustaining is a job, and it's a very hard job. The shareholders might not like that job or want to do a different one, or they just can't do it. Or the market is going down, but someone could use the IP/assets/team.
Who said infinite? Startup founders that got investments have designed the exit points based on market conditions, and nobody would trust "infinite". It's just like stock investments (unless you "invest" based on feelings, of course) - you calculate the risk, the potential, and then you decide. Nobody reasonable puts "infinite growth" into their Excel sheets.
And yes, growing until that exit point is a lot of work - so it makes total sense people want an exit at some point.
No, that's not true. There are plenty of stable market capitalization, dividend-generating public companies. Their cap-to-EBITDA ratio is much smaller, but that doesn't change the fact.
Of course everybody expects the company to take advantage of opportunities - but it has to make economical sense. Nobody wants their company to try to grow so hard the whole company crashes.
Perhaps the founders want to remain there and grow, perhaps they want to focus on something else or retire. Perhaps the plan always was to sell after X years - I don't see anything wrong about that, still better to innovate&sell than just buy stock&sell IMHO.
You can't attract investors if they can't sell in case the investment is successful. This is severely limiting and a terrible situation to be in - especially if you already have investors, who might demand their money back from you - way before your profits could cover it.
And the worst thing that might happen - you design a startup to be acquired by Microsoft/Apple/Google and then EU comes and says no. WTF?
Why would competition law and/or national security laws not apply to a start-up or its acquirers? Why would they or their acquirers get exceptions? Would those exceptions cover patents as well on the national security? What else and why?
Also, this isn't the EU saying "no" at the moment, but looking into it, as it does with many things.
They shouldn't get exceptions. There shouldn't be so many laws and regulations that result in EU being so behind economy-, success- and investment-wise.
I have no idea. I’d imagine using a light shield increases the relative brightness of the displays, which could be important to Apple.
Some users cannot use the thinnest lightshield: their eyes or eyelashes touch the lens.
Apple did make them interchangeable and exchangeable (for free), so it seems like the major FOV issue is with their scanning and auto-selection (for some users).
Wow, I'd love to witness something like that one day. My circle doesn't include a lot of these people, and maybe that in itself is part of the more general problem.
What you’re seeing is exactly that, engineers and researchers in charge, trying to communicate by emulating stuff they don’t understand. Product people need to be involved to find a market fit for all this great tech.
Any US citizen HAS to leave the US with their nationality. That’s the law.
U.S. citizens must use a U.S. passport to enter and leave the United States. This requirement is outlined in the U.S. Code of Federal Regulations, specifically 22 CFR 53.1. It states that a U.S. citizen must possess a valid U.S. passport to depart from or enter the United States unless they meet certain exceptions. This law ensures that U.S. citizens are properly documented for international travel, facilitating legal entry and exit from the country.
Right, but the only punishment for failing to comply is reprimand and delay at the entrance while trying to verify citizenship. The latest publicly available CBP Inspector's Field manual is unequivocal that if the Inspector is convinced the entrant is an American citizen they cannot stop them from entering.
The law really exists as a way to avoid delays at entry as a US citizen having a valid US passport can be processed in much faster than one who does not, and it minimizes the risk of being stuck with an immigration agent that does not belive your claims of being an American citizen due to lacking convincing records and documents.
American Citizens are not the only ones with an unequivocal right to enter. American Indians born in Canada who have are at least 50% American Indian by blood "cannot be denied admission to the United States". They are required to prove to the inspector that they meet this criteria, but if they do, they don't need a passport or anything. (But they probably needed some documents to convince the inspector of their status as a 50%+ native born in Canada.)
While the law does indeed state that, there are no penalties whatsoever defined for breaking the law, so there are literally no consequences for doing so.
It's completely unenforced. When exiting the US no American authority checks what passport you are using to leave, and when entering they are legally required to let Americans reenter the country. At worst the border guard will be cranky and give you a stern lecture about how you are supposed to use your US passport.
