What is dark matter? – with Peter Fisher

What exactly is dark matter? We can’t see it, but we can observe its ghostly gravitational effects on the behaviour and evolution of galaxies.

Join particle physicist Peter Fisher as he explores leading-edge research focused on revealing dark matter’s true nature and what it will mean to science when we do.

In this talk, discover the mysterious, nonluminous form of matter that is believed to account for about 27 percent of the mass-energy balance in the universe.

This talk was recorded on 6 September 2022.

Peter Fisher is a professor in the Physics Department at MIT and currently serves as department head. He carries out research in particle physics in the areas of dark matter detection and the development of new kinds of particle detectors. He also has an interest in compact energy supplies and wireless energy transmission. Peter received a BS Engineering Physics from Berkeley in 1983 and a Ph.D. in Nuclear Physics from Caltech in 1988.

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[JPage-fjmb]

"We know dark matter exists by the way the universe is shaped." ...Which we don't actually KNOW at all, but have calculated mathematically and also built a whole mathematical framework to support, and if that's wrong, well, we know nothing. We made our equations agree with each other and input variables we can't explain to make them come out right. Proof! Great science there.

[ColdHawk]

The long and short of this lecture, like every other talk about Dark Matter, seems to be we are still in the dark about the matter.

[Simbosan]

56 minutes to say "we don't know"

[shawns]

The missing mass is dilated mass. We have all heard the phrase "mass becomes infinite at the speed of light" this phenomenon is illustrated in a common relativity graph with velocity (from stationary to the speed of light) on the horizontal line and dilation (sometimes called gamma or y) on the vertical line. Mass that is dilated is smeared through spacetime relative to an outside/stationary/Earthbound observer.
Wherever you have an astronomical quantity of mass, dilation will occur because high mass means high momentum. There is no place in the universe where mass is more concentrated than at the center of a galaxy.
In the 1939 journal "Annals of Mathematics" Einstein wrote about dilation occurring in regions that would have less mass than that which would exist at the center of common spiral galaxies. Therefore it is safe to say that according to Einstein's math the mass at the center of our own galaxy must be dilated, in other words that mass is all around us.
It was recently discovered that low mass galaxies (like NGC 1052-DF2) have normal star rotation rates. This is what relativity would predict because there is an insufficient quantity of mass at the center to achieve relativistic velocities.
A simple way to confirm this would be to calculate the star rotation rates of a large number of galaxies. This would show that all the high mass galaxies would have star rotation rates that seem to defy the known laws of physics and all the low mass galaxies would have predictable star rotation rates.

[alexbowman]

Yes the trumpet shaped Universe, the big band theory.

[dirremoire]

"we know dark matter exists because all our suppositions and theories about how the universe works can't possibly be wrong."

[johnmcclain]

I have long found, I get as much understanding out of reading many of the comments, as I do from the lecture itself. The questions raised are answered by other watchers, or the presenter, and they typically are questions beyond and outside of the direct aspects of the lecture. This is certainly true regarding this lecture. Thanks!

[jacobsmith]

Dark matter is a theory to explain another theory they’re having trouble to explain.

[alexbowman]

I can’t believe he’s written a book on something which almost certainly doesn’t exist, some people have spent a career on it.

[jimmyquigley]

Dark matter is a hypothesis which allows a mathematical description of "local" anomalies in the fabric of space-time. Dark energy allows a description of the observed anomaly of accelerating cosmic expansion. Both hypotheses require a total of 20 times more stuff than the observable universe to fudge a correspondence between observation and theory. New physics is needed, but I don't know what it would look like.

[jennabronson]

“We know that dark matter exists.” LOLno. We know that some observations don’t match what we expect from certain physical models. That doesn’t mean we should go drawing epicycles.

[davebeech]

Just throwing out an idea here: we're told that large bodies create gravity by 'bending' space-time, like a bowling ball on rubber sheet, to use a common analogy. Maybe the reason the galaxies spin the way they do is because, instead of bending, the fabric of space-time itself is spinning like an enormous disc, carrying the stars and galaxy with it. That's why they all move at the same speed. I fully expect any half-way competent astrophysicist to explain why I'm wrong. I'd appreciate the lesson.

[peter]

TLDR:
Dark matter is a theoretical magical matter that was invented over 100 years ago by some guy who applied newtons law while looking at a galaxy and realized that the outer most objects were not spinning around the galactic center as slow as orbital mechanics dictated. They did move at the right speed if the guy toke into account that the galaxy was heavier then he estimated the weight to be at. To him, fudging the numbers to get the right answer meant that the problem was that he was not seeing the missing matter instead of assuming the math to be wrong. Because maths in a era they had not gone to the moon yes was obviously not flawed, he theorized that there is somehow a dark, invisible form of matter.

Modern dark matter believers say that over 70% of the universe matter is dark matter, how every they are not able to detect or prove that it exist.
In essence dark matter is the modern version of "i dont understand lighting, therefore it is god who is angry".

Currently there is a lot of scientist who are working with models to fix the equation that we use for gravity. In essence fixing the math instead of inventing something that clearly does not exist. Turns out, most of these works require just a minute adjustment, Sadly, the belief in dark matter which goes against the scientific principle is so encrusted now that to prove the dark matter believers wrong, their mathematical formula has to essentially also account for all the dumb shit they also say is the work of dark matter which is ridiculous since they basically have to prove the earth is round and as far as we know also show that the same proof explains why the mitochondria is the powerhouse of the cell, too things that as far as we know are unrelated except they have no proof.

Basicaly, Dark matter believes are religious extremist with no proof for anything because its all theoretical since we are stuck on this planet.

[grizzlednerd]

Takes me back to a maths lecturer I had who couldn't make eye contact...

[Yuri_Panbolsky]

Three scientific lines without dark substances -
1. "First test of Verlinde's theory of Emergent Gravity using Weak Gravitational Lensing measurements"
"Understanding galaxy rotation curves with Verlinde's emergent gravity"
2. "Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies"
3. "Galactic rotation curve and dark matter according to gravitomagnetism"

[Im_MarkS]

Did i miss the answer ? I still don’t know what dark matter is, i know what it isn’t

[ErnestSemerda]

Dark matter = we have no idea wtf it is... Update today = we still have no idea wtf it is.. until next time. Brought to you by experts you have to trust.

[albuslava]

"Information is information, not matter or energy.
No materialism, which does not admit this, can
survive at the present day" by Norbert Wiener, the Father of Cybernetics.
If physics wish to survive, than have to recognize the same ontological status of Information, Matter and Energy. That is a key for paving the way to new physics. Because of the fact that physics treats the information as just an artifact of interaction of matter and energy, even at quantum level - no way to detect Dark Matter. Physics should embrace the idea that information can play also a cause role, not only as an effect's one.
Thanks for nice and instrumental talk - very interesting.

[solomonlalani]

Humanity needs a major breakthrough in particle / Quantum physics. I know it is a marathon, not entirely under control...but without a major breakthrough, the knowledge and this branch of science are becoming stagnant. To be clear, I am not undermining the objectives of countless physicists, and scientists working in the field. I hope we find a major breakthrough soon.

[StevenJiaWeiXU]

I still don't understand what is dark matter after attending this lecture.