The Biggest Ideas in the Universe | Q&A 17 - Matter

[@Dr10Jeeps]

I'm certainly going to miss these sessions with Dr. Carroll when he stops. The internet needs much more of this type of content. Personally, I would love to see the internet filled with podcasts dealing with the social, biological, and physical sciences. People need to be educated.

[@kobev3li385]

As soon as my brain registered that you were talking about why gauge bosons, and fermions have their respective spins, I had to immediately drop everything I was doing. As always, an extremely elegant characterisation to these complex topics. I am so thankful for this wonderful series, keep up the great work Dr. Carroll !!!

[@rc5989]

I particularly enjoyed Sean Carroll explaining how cosmologists and quantum physicists sometimes use the same or similar terminology to mean different things. These distinctions are probably elementary to trained physicists, but not to the average viewer. Almost as a throw away, Dr. Carroll explains how understanding what scientists mean by the word ‘matter’ turns out to be important. I am comfortable with the broad strokes of familiarity enough that “It’s all fields, all the time.” However, it never dawned on me until this video that the forces in nature can therefor be considered matter just as much as so called particles. I know he repeated this several times previously, but I get it now finally. It is really really really all fields. All the so called forces, all the so called particles, these are all excitations in fundamental fields of nature. Period. The end. That’s it. Which is actually the beginning, because so many supposed paradoxes or mysterious features of quantum mechanics are actually not mysterious at all (or much less so) because we don’t have to tell ourselves the “particles & forces” stories which are only crude visualization tools compared to what is really going on.

[@salvatronprime9882]

I've been thinking exactly this, regarding fields, and repeating it to whoever would listen. I don't even see the point of thinking too much about electrons and particles to begin with. People intrinsically understand fields, and you can show a magnetic field very easily. The part where he draws the graph with the particle energies is so simple and captures most of what the general public needs to know about particles. The overall physics conversation should go back to fields. Quantum physics isn't "crazy" or "weird" or "mysterious". Fields make sense.

[@akumar7366]

Weekend treat, thank you Sir.

[@quahntasy]

Yea made our weekends

[@quahntasy]

*So many great questions and such nice answers. Thanks for making our weekends*

[@I2yantheGreat]

Thank you Simpson's-style disembodied head of Sean Carroll!

[@brankooffice]

So many questions I had answered in this video. Great work!

[@rhondagoodloe3275]

Sean, Thanks for doing this series. Sorry to hear it's not infinite. I'm hoping the version of me lands in the branch of the world where the series continues.

[@paulc96]

Thanks again Prof. Carroll, for these superb lectures. Sorry - I mean videos.

[@notmyrealnameful]

These talks are great, but one observation about Sean’s descriptions. Sometimes the math is used to describe why nature is a certain way. For example, the graviton is a spin2 particle because it has two spacetime indices. This feels like putting the cart before the horse. Gravitons don’t have little indices attached to them. We might say instead that our model of the graviton has two spacetime indices and that description is consistent with observing a spin2 particle. So we are confident that we will observe the graviton to be spin2 and if it isn’t then we will need to revisit our model and perhaps change the indices in some way. I don’t expect this is contentious, and I can understand physicists omitting to mention it all the time because it is simply a given. But it can contribute to a prejudice that maths is unreasonably effective at describing the universe. The alternative view is that maths is simply a very effective abstract language that could describe any universe.

[@kindlin]

I like to imagine the NS turning into a BH is throwing the neutron-ness out the window. If anything like a singularity exists (which theoretically is infinitely dense, but in 'reality' could be on the order of the planck scale) the quarks must be so packed they are basically on top of each other, and maybe reach some quark degeneracy pressure, or if string theory is correct, a string degeneracy pressure where you just cannot pack the individual quark strings any closer. I like to imagine the 1D strings (I'm a fan of string theory) are turning into something like your headphone cables, just getting all warped around each other in a Kaluza-Klein manifold. Being 1D, you could say they infinitely warp themselves, ever approaching a true singularity, but that would also take infinite time, so no 'true' singularity will ever exist in our universe.

[@argosron9838]

This universe itself is a singularity, did you miss it ?

[@kindlin]

@@argosron9838 Is this the theory where every black hole is actually a new universe/big bang? I do not adhere to this nonsense!

[@stepananokhin693]

I just wonder.... 1. As we know Einstein's equation says that distribution of masses, momentum and energy determine geometry of space-time. 2. According to quantum mechanics matter could be in a superposition of states. Do 1 and 2 imply that geometry of space-time (space-time itself) could be in a superposition of multiple states?

[@lilitvehuni6402]

Doesn’t that mean multiple universes?

[@cosmichappening1712]

If you mean different dimensions and levels of perception, then yes.

[@gisteron]

Regarding 26:10 The Stern-Gerlach experiment was made with electrically neutral silver atoms. The entire point was that these were *not* charged particles deflected by a magnetic field, but *neutral* ones, deflected only because of an internal magnetic moment - which at first they interpreted as orbital angular momentum, not knowing that the total orbital angular momentum of the electron shell of silver is in fact zero in its ground state - coupling to an inhomogeneous external field.

[@Nosirrbro]

I believe there is at least some reason to think that strange matter can be formed at sufficient pressures, and it could grow to contain an arbitrarily large number of quarks not confined into any sort of specific particle, which may even be more stable than regular matter at any pressure. However, what that reason is, or how compelling of an argument it makes, I couldn't tell you. The wikipedia article isn't much help either en.wikipedia.org/wiki/Strange_matter

[@protoword10]

Doctor Carroll, one of major reasons I wanted come back from hiking vacation sooner is your lectures. Than you! One question remain to puzzles me: Is it possible to measure movement and density of dark matter with help of gravitational lensing?

[@TheD4VR0S]

possibly but there are otherways to measure the density of dark matter like rotation speed of outer stars in galaxies

[@protoword10]

David Davies I agree, I know it, my point is: How dark matter is spread, evenly or in clusters!? It can tel us more about it’s nature!

[@TheD4VR0S]

@@protoword10 Its clustered around galaxies read this (especially the paragraph entitled The Bullet Cluster) arstechnica.com/science/2017/02/a-history-of-dark-matter/

[@protoword10]

David Davies Thanks!

[@bernardmcgarvey4169]

At about 9:00 you talk about particles with some speed - but what is that speed measured relative to? I am sitting at my table at rest but there are some particles somewhere that relative to my speed is close to c.

[@JasonWalsh-b4n]

ARE BOSONS MADE OF MATTER?

[@rickharold7884]

Awesome. Love these

[@velinkovac9583]

How can I find video about Entanglement? Sorry cant go through all 48 videos, but in the playlist there is no information about the which video content is in some selected video.. you can see only generic title..

[@gtziavelis]

Matter matters.

[@patbl61]

😂👍

[@pamelacollins1153]

Does the creation of the neutron star have anything to do with the uncertainty principle?

[@Wanttofanta]

"What do you mean by 'matter'?" "I think....I forget exactly." Sean Carroll quotes out of context :P

[@isaacanderson8231]

Can’t wait to watch

[@tovarischkrasnyjeshi]

I'm sure you've heard but like a week or so ago news hit of a gravity wave detection of iirc 23 M[sun] black hole and something between the masses of the largest neutron stars known and under the masses of the smallest black holes known at 2.6 M[sun]. A lot of popularizers have cautiously leaned in on it maybe being a quark star - I think Matt O'Dowd with PBS's space time got into it.

[@davidhand9721]

Let's say I have two electrons and I'm going to throw one at the other. You're telling us that the Pauli exclusion principle will stop them from overlapping, presumably causing them to bounce off or something. However, the PEP only prevents electrons from sharing the exact same state; if they are moving toward each other, they have different momenta and therefore are unaffected by the PEP. What, then, stops them from passing through each other? It seems like the principle is so exact that it ought to be of no consequence at all to two systems interacting such as two atoms as there are so many degrees of freedom and energy gradients. Yeah, I still don't get it.

[@w6wdh]

The interesting stuff seems to occur, not when the electrons are freely moving, but when they are confined (electrons in a box, electrons in an atom). That’s when their energy levels become quantized, and no two electrons can have the same quantum state, due to the PEP, as you put it. A free electron can have any energy and spin any way it wants to. It’s not interacting. (I’m assuming it’s not entangled with anything.) If you throw two electrons at each other, they will bounce off each other just due to their mutual electrostatic repulsion, which is HUGE at atomic distances. If you drop an electron into a positive ion (an atom missing an electron), the atom can gobble up the electron and emit a photon with the excess energy of the electron. The electron’s state (energy, spin) will be quantized and it will have to be different from all the other electrons already in the atom. PEP at work.

[@voges1001]

Electromagnetism

[@TheD4VR0S]

Black holes evaporate so when they reach a low enough mass do they revert to neutron stars ?

[@FreekaPista]

No. Black Holes will always have an infinite density, regardless of how small the mass is. We can create very very very low mass black holes, which evaporate to nothing almost instantly. There's no point at which a black hole has "too little mass" as long as: it's not massless, it had an infinite density at some point in its past.

[@TheD4VR0S]

@@FreekaPista Thanks

[@TheD4VR0S]

@@FreekaPista Thinking about it more i'm still unsure, the reason a black hole has it's density is because of the gravity and the gravity is produced by the mass, so if it evaporates there will at some point be insufficient mass to generate the gravity to compress the matter and density will fall , if we could compress the earth to the size of a tennis ball the gravity remains the same - you say "Black Holes will always have an infinite density, regardless of how small the mass is." but how could a low amount of mass create enough gravity to compress the matter to infinite density ? If the black hole evaporates then the mass drops therefore the gravity that is making the mass dense drops therefore the density drops ? (gravity is independent of density)

[@w6wdh]

David Davies As the mass of a black hole decreases, due to its black body temperature and emission of Hawking radiation, its temperature increases. It increases very very slowly at first, but as a critical threshold is reached (possibly after billions of years), its temperature becomes huge and the black hole would cease to exist in an explosion that would be similar to an atomic bomb. In other words, if you could make a small black hole, you wouldn’t want to be anywhere near it.

[@Name-js5uq]

You certainly are a treasure and a joy to listen to I must say and I really enjoy everything you have to offer I was just curious and wondering if you could perhaps please change that awful background of the bricks please?

[@Stellarcrete]

At ~41:00 Sean says "No, Pauli's Exclusion principle is not being violated when a white dwarf becomes a black hole." Then proceeds to tell us he is unclear how that happens and quantum mechanics has nothing to do with attempting to explain it. Bro, love ya but just say: "Yea, black holes destroy quantum mechanics. Pauli's Exclusion principle and black holes are mutually exclusive."

[@anthonydevito8309]

why don't we have print of the lectures for us hard of hearing....reading is better than merely listening

[@patrickmchargue7122]

What is the force that enforces (*cough*) the Pauli exclusion?

[@Nosirrbro]

He half-addressed half-dodged that question in the original matter video, his argument was basically that the idea of forces was sort of outdated and we use it when talking about phenomena that have their own force particles because its convenient, but in this case it doesn't really act like that, instead its better to talk about it as nothing more than the way the equations of motion of the wave function evolve. At least, I hope I remembered what he said correctly.

[@patrickmchargue7122]

@@Nosirrbro Thanks

[@joshua3171]

so can * be used with n!

[@joshua3171]

cheers for all the shows from Mr Carroll and friends

[@FABRIZIOZPH]

first like :)

[@FABRIZIOZPH]

@Anifco67 I don't really care if people care.. I just felt like posting that..

[@asolarasolarasolar]

@@FABRIZIOZPH That's punk! hahah