#5minphysics 

Brian Green and Lawrence Krause have met before. I saw them one together on a stage. Nice vid. It's somewhere on YT ...

I enjoy Sean very much. It's a wonderful time for youtube with all the great minds releasing their own content. I enjoy music, sports, and the arts very much, but also think we undervalue people with great minds. I enjoy a good voice box that can sing or a foot/arm that can kick/throw a ball, but for me, the mind has it all.

if the neutron star becomes sufficiently massive in this way, it would collapse into a black hole.. the neutrons would eventually break down into their quark constituents as the system collapsed..

Mark has a good point though, according your own reasoning. Somebody just has to do the calculation.

If neutrons were to break into quarks should then the black hole suddenly loose a drastic amount of mass?

@@markmd9 no.. the neutron doesn't break up into quarks until the the thermal energy associated with the quarks is at least equivalent to the neutron mass..., and E=mc^2 means the black hole doesn't lose mass.

Андрей Бахарковскй If i keep a constant speed and go vertical somehow. Lets say in a weak rocket with an enormous fueltank. Tell me why I wouldn’t get to space some day.

Андрей Бахарковскй But surely if I travel away from the earth at 5mph and started falling back to earth, I wouldn’t be travelling at 5mph anymore.

Андрей Бахарковскй Ok, I’ve looked it up now. Which arguably I should have done to begin with. The escape velocity for earth is 11,186 m/s (6.951 mi/s; 40,270 km/h; 36,700 ft/s; 25,020 mph; 21,744 kn). But my point is, that even if a rocket travels at 95% of that, it would still get to space, because it is constantly propelled. And by extension it would also do that at 50% of that speed. What I had always missed from these explanations is that when talking about the escape velocity we are implying a “free, non-propelled object”, which a rocket isn’t. So it’s not bound by the escape velocity.

black holes can swallow other black holes.. that is basically what happens when they merge.

@@lkrauss1 But if a black hole swallows anorher black hole it simply becomes a bigger black hole. Andrew is saying that if our universe is the interior of a black hole, then stars that collapse to form black holes are indeed black holes within the black hole that is our universe.

@@lkrauss1 this is not what I meant, sorry. Perhaps it's my English ;). We have black holes in our Universe. They don't seem to be 'merged' with anything around. They rather look very separate from the rest of the stuff around them. If a black hole merges with another one then we just have a bigger black hole. So... either our universe is not a black hole, or outside of our universe physics of black holes is different but... would we still call them black holes? ;) Just a thought. I think you've pulled my leg into a black hole with this episode ;).

@@user-sl5nm9js8p I hope I can pull it out.. the short answer is, in a large enough black hole you can have lots of intact objects that fall inside of it, including smaller black holes.. Now something to keep you up.. from the inside the black hole can look like it is expanding, but from the outside it would appear like it is contracting.. :)

@@lkrauss1 Does that mean that black holes have uneven density distribution? Does stuff behind an event horizon is not actually equally dense? Sorry if I'm wrong but my guess was that it actually is very uniform.

we can generally talk only about local quantities in GR.. some global quantities are important.. if the universe is closed on the largest scales, then that is consistent with being flat on observable scales.

@@lkrauss1 Firstly, thanks very much for taking the time to do 5 minute physics Lawrence, its much appreciated. "if the universe is closed on the largest scales, then that is consistent with being flat on observable scales" You mean in terms of our inability to measure accurately enough to detect such a small degree of curvature on observable scales? If not I'm confused.

no.. you are correct.. I was talking about the mass the moment the black hole forms.. it will later collapse to a point, at least if general relativity is accurate all the way down... and if our universe were closed, ignoring dark energy for the moment, which changes everything, then it too would eventually collapse to a point.

no... once a black hole always a black hole... unless it evaporates.. see tomorrow's video. and once a closed universe always a closed universe..

@@lkrauss1 If the universe is indeed closed... But our best measurements to date suggest the universe could be flat thus infinate. If so, given that inflation is correct, when the inflaton field stopped expanding, the resulting hot big bang would have occured across the entire infinite universe simultaneously. I then wonder, in the distant future, when the expansion of the universe has left us with just a field, a scalar field identical to the pre hot big bang scalar field, if it too would cease its expansion, another phase change and another hot big bang. A cyclic universe. I am of course uneducated in this field and probably talking nonsense.

@@lkrauss1 I will definitely tune in tomorrow. :-)