Anyone come across this new YouTube channel?

[pbuk]

I'm not sure how wrong this guy Monroe Pattillo is, or if he is just a bad explainer: .

 

[Bandersnatch]

Don't know the channel. I skimmed over the slides and listened to some of the audio. And while I'd take issue with quite a number of statements, it's not egregiously incorrect.
I am in a forgiving mood, though.

Is there a particular reason for your posting this here? Are you looking for a review or corrections? Something else? Not sure what response you're after.

 

[pbuk]

it's not egregiously incorrect. I am in a forgiving mood, though.

Very forgiving! Some of the more egregious errors in the 10% I looked at (basically the beginning and the end):

On the first slide (visible from about 20s in) where he explains that our current understanding of the universe, and in particular the size of the observable universe:

• is limited by our inability to observe light redshifted beyond microwave ("[Maybe] we aren't looking far enough shifted")
• presumes that that the acceleration of the universe is constant

34:12 "I've always thought that dark matter is nothing more than photon wavelengths that we can't observe anymore"

38:01 (on cosmic expansion) "It could be that if you have a high enough density of quarks that you'll rupture spacetime to create new spacetime that's literally a void that goes on forever and the universe squirts itself out into nothingness at a speed that changes as the expansion stabilizes"

Is there a particular reason for your posting this here?

I thought forum members might be interested.

 

[PeterDonis]

I thought forum members might be interested.

This illustrates why we don't normally accept YouTube videos as valid references, and require textbooks or peer-reviewed papers.

 

[Bandersnatch]

Very forgiving!

Fair enough.

I've given it a proper listen, and while I had thought there might be some value in listing all the errors, there's just too many of them. A good bulk of those stems from a fundamental misunderstanding of what Hubble constant/parameter represents.
The title, at least, is correct.

 

[Jaime Rudas]

The title, at least, is correct.

Only if the universe is finite

 

[berkeman]

The title, at least, is correct.

Maybe if we ignore normal English grammar modulo artistic license.

 

[Jaime Rudas]

The title, at least, is correct.

If the universe is infinite, can it become even vaster?

 

[PAllen]

If the universe is infinite, can it become even vaster?

It can become vaster per unit of stuff, everywhere. There are different metrics you can put on an infinite spacetime, and only some have this geometric property. The invariant description of the geometric property is that the spacetime admits an everywhere expanding congruence. Thus, for example, Minkowski spacetime does not have this property. That’s why the Milne congruence can only fill a piece of Minkowski space. Note, this definition of an expanding spacetime is decoupled from any requirements of isotropy or homogeneity.

 

[Jaime Rudas]

It can become vaster per unit of stuff, everywhere.

Yes, its density can decrease, but this doesn't mean the (infinite) universe as a whole will become vaster

 

[PeterDonis]

Only if the universe is finite

The observable universe is finite and its size is increasing, and the title might be referring to that (though it's hard to tell--again, this illustrates why we prefer not to use YouTube videos as references).

 

[Jaime Rudas]

The observable universe is finite and its size is increasing, and the title might be referring to that

Yes, that's why I stated "only if the universe is finite."

 

[PAllen]

Yes, its density can decrease, but this doesn't mean the (infinite) universe as a whole will become vaster

But being able to have density decrease everywhere is a very unusual geometric property for an infinite spacetime to have. I would tolerate the description everything everywhere is getting vaster as a metaphor.

 

[Jaime Rudas]

But being able to have density decrease everywhere is a very unusual geometric property for an infinite spacetime to have. I would tolerate the description everything everywhere is getting vaster as a metaphor.

Yes, I understand now. The title is correct, and I, once again, am wrong.

 

[PeterDonis]

Yes, that's why I stated "only if the universe is finite."

The observable universe is always finite, regardless of whether the universe as a whole is. So if you meant "observable universe", your "only" makes no sense. It only makes sense if you are referring to models in which the universe as a whole is spatially finite.

 

[Jaime Rudas]

The observable universe is always finite, regardless of whether the universe as a whole is. So if you meant "observable universe", your "only" makes no sense. It only makes sense if you are referring to models in which the universe as a whole is spatially finite.

Yes, I understand now. The title is correct, and I, once again, am wrong.

 

[sbrothy]

Maybe if we ignore normal English grammar modulo artistic license.

I found this remark funny and I'm not even a native English speaker!

 

[PAllen]

Yes, I understand now. The title is correct, and I, once again, am wrong.

Oh come on. All I was saying is that there is a possible way to look at such that the title is right. That doesn't mean your way of looking at it is wrong, or than any title can capture more than a small piece of the whole truth.

 

[berkeman]

Thread is closed temporarily for Moderation.

 

[berkeman]

After deleting a post with an insult, the thread is reopened provisionally.