What does the universe expand into? Do we expand with it?

Could it be that the universe does not expand but we shrink instead? What does it mean that the universe expands anyway? And if it does, what does it expand into? In this video I tell you what you need to know about Albert Einstein's General Relativity to make sense of all this.

Correction to the illustration at 3 mins 31 seconds: It should just have been "smaller than 2 Pi R", not "R smaller than 2 Pi R" (which is correct, but makes no sense). Sorry about that!

0:00 Intro
0:54 How General Relativity works
5:52 What does the universe expand into?
7:01 Do we expand with the universe?
7:39 Do we shrink?
8:58 Summary
9:38 Sponsor Message

#physics #space #universe

[SabineHossenfelder]

Several people have pointed out to me that there is a fake account posting here (and possibly elsewhere) under my name. This account has been reported (by me and several other people). But since this may happen again please be advised that the "real" me has a checkmark after the name.

[jppcasey]

As I get older, I can confirm without any doubt that I am expanding.

[janoldland]

I'm just a 77 year old, who barely graduated high school. I've always enjoyed thinking and speculating about this subject. It's just SO fascinating. Thank you for your helping to understand space/time. I may never understand it all, but trying to is wonderful for the brain.👏👏

[blinkingmanchannel]

Feynman would be proud of your efforts here. The physics is amazing, and I haven’t found a doorway into it until now. I’m probably not smart enough, given my teachers all seem to just turn their backs and start drawing equations. But you do a great job of showing what we’re trying to get at with the equations. The sphere inside a cube, plus the subsequent minute or so of explanation cleared a big chunk of confusion from my mind. (Well, I feel better anyway…) I have been trying to get to grips with curved spacetime… This at least helps me see what my question should have included but didn’t. Outstanding!❤

[ryoung]

You need to correct the part about "R < 2pi R" [sic] at 3:30—both in the VO, and in the graphic.

[guest_informant]

"Cylinders are internally flat."
I might have to think about that for a few years.

[LutchoCressoni]

The reason people ask you even though there are other videos is because you make it interesting! Even being a physicist myself, I love the way you explain things.

[adbuuk]

Love your no-nonsense approach to physic.

[Finnec]

"The part about my job that bothers me most is the need to work on something that is popular or to work with people who are popular. I have always had, and still have, trouble funding my research because I tend to be interested in topics that few of my colleagues find relevant. I almost left academia because of this several times, and I still feel every other year that academia just isn’t for me. If I can only get funding to work on research I don’t consider promising, then what’s the point?"

- Sabine 2020, physicsworld, "ask me anything"

We recognize her.

[carlbrenninkmeijer]

Thank you. The fact that so many view your videos explaining abstract "things" within one day, gives me confidence in the future.

[radiowallofsound]

Sabine I really admire the way you think and explain things out. We're very lucky to have someone like you spending time on making these contents, it is much appreciated!

[ChimeraActual]

You have blossomed in the past year! Love you.

Are there respected cosmologists who aren't satisfied by this explanation? That is, are there competing explanations? Competing questions?

A non-cosmologist can't rule out that this may be the wrong solution fork or simply begs the question.

[Flashfox_Prime]

Now for a compliment - I discovered your channel after an episode of PBS' Space Time (which I have been following for years). Since then, I have also been following your podcasts and really enjoy how you explain complicated matters in understandable ways for us non-physicists. I look forward to every podcast :-)

[europaeuropa]

My knowledge just expanded although it didn't expand into anything.

[strawbarry]

I love these videos, but generally get lost about halfway through. It's like a switch in my head and my brain goes "Welp, I'm out." But what encourages me is that there are people like Einstein/Sabine who really *do* understand this stuff, which gives me hope for the human race. Just think, roughly 3 pounds of physical brain can approach understanding the reality of the universe. That is just...magnificent.

[malcolmcrossley]

Thank you so much Sabine, your insights and explanations have been testing my understanding of the universe in the most amazing way.
I watch each of your videos intently and stop, watch, rewind and proceed until I am satisfied that I have unpacked and understood what you have said.
I feel like I have my own personal lecturer.
Thank you so much for your time and efforts in bringing these most amazing and interesting topics to the world in a wonderful and fun way.

[rajshikhargupta]

Dr. Sabine Hossenfelder, I am just binge-watching your videos because they are soo good. I know that as a Ph.D. student I am not supposed to waste so much time on youtube but I really cannot help it... they are just soo good. Thanks for making these.

[MeppyMan]

I was going to get an early night. But this is one of my favourite topics.

[DoctorHomunculous]

Do atoms and/or gravitationally-bound structures "feel" the expansion of space? ie. does the nuclear force fight against the expansion? And one more question: Does the time dimension also expand?

[edlaw]

Sabine Hossenfelder opens doorways to understanding like no other instructor. Five Golden Stars for Dr. H!!