The h Bar

12:00 AM

> If the old image of the Big Bang was of a white dot appearing in a plane, the new image is of an entire endless plane becoming suddenly illuminated in every part. You might visualize a sheet of light settling down upon the plane; indeed, one current model views the universe as pair of parallel spaces that oscillate back and forth, creating a Big Bang each time they pass through each other.

so it appears that is an actual cosmology theory in philosophy, not someone's pet theory

taken from infinity and the mind

GPhys

2:32 AM

11 hours until EHT results ~it's happening~

Akash. B

4:29 AM

@JohnRennie

John Rennie

@Akash.B morning :-)

Akash. B

@JohnRennie so let me present my theory

universe expands as long as black holes exist

@JohnRennie what tool are you using for drawing?

John Rennie

@Akash.B I use Google Draw to create drawings, then I copy and paste the drawing into Windows Paint and save it as a GIF so I can upload it here.

Akash. B

@JohnRennie can you give me a link?

John Rennie

docs.google.com/drawings

Akash. B

4:57 AM

John Rennie

Cool :-)

Akash. B

@JohnRennie my theory is simple

Stephen Hawkings once told that the mass in the black hole would be converted into energy and get radiated as many radiations

John Rennie

It's always good fun to try and thing about ideas like why the universe is expanding, but constructing something that physicists would regard as a theory is a lot harder.

Akash. B

@JohnRennie yeah

John Rennie

In physics a theory basically means equations that we can do calculations with.

Akash. B

5:01 AM

it lacks mathematical support

okay let me get back to it

John Rennie

The theory we currently use to describe the universe is general relativity. That gives us equations to describe the universe, and when we solve them we find the universe is expanding.

Akash. B

I will give try to equation when I have a P Hd

I am just telling only possibilities

John Rennie

Don't stop coming up with the ideas. I used to do exactly the same as your age. Sadly when I learned physics I discovered most of my ideas were wrong. Oh well :-)

Akash. B

so as it looses its mass the space time would stretch

@JohnRennie just for fun

@JohnRennie okay so far?

John Rennie

5:23 AM

@Akash.B it's hard to see how the black hole would affect parts of the universe that are billions of light years away, and yet we see that all parts of the universe are expanding, even those parts right at the edge of the observable universe.

Emilio Pisanty

@SirCumference fictitious forces

Akash. B

5:58 AM

@JohnRennie can we prove it using mathematics?

John Rennie

@Akash.B the equation that we use to describe the expansion of the universe is derived from Einstein's equation for general relativity, and it's called the FLRW metric.

Friedmann–Lemaître–Robertson–Walker metric

The Friedmann–Lemaître–Robertson–Walker (FLRW) metric is an exact solution of Einstein's field equations of general relativity; it describes a homogeneous, isotropic, expanding (or otherwise, contracting) universe that is path-connected, but not necessarily simply connected. The general form of the metric follows from the geometric properties of homogeneity and isotropy; Einstein's field equations are only needed to derive the scale factor of the universe as a function of time. Depending on geographical or historical preferences, the set of the four scientists – Alexander Friedmann, Georges Lemaître...

Akash. B

@JohnRennie okay so can we prove it?

John Rennie

The way we test our theories is to compare them with observations. So we study the universe (using telescopes) and see how well it matches the predictions made using general relativity.

Akash. B

6:15 AM

@JohnRennie how far is Cygnus?

John Rennie

@Akash.B don't know. What does Google say?

Akash. B

@JohnRennie 6,197 light years

@JohnRennie is this that much far ,then how did it was found?

undefined

would it be okay to mail an author of a paper and ask him, if you would send me a copy of his paper, when the paper is only published behind a paywall magazine?

Emilio Pisanty

@undefined yes, that's perfectly OK

John Rennie

@Akash.B I don't know how the distance was measured ...

undefined

6:26 AM

thanks :)

Emilio Pisanty

though check first that there is in fact no open-access copy, using e.g. Unpaywall

undefined

I did but I'll double check

Akash. B

@JohnRennie if it is possible to find a black hole many miles from earth ,then we can observe and prove it

Emilio Pisanty

also note that there are not-fully-legal ways to obtain copies of such papers that are faster than email-the-author

(i.e. it's illegal for the site to distribute the copies, it's arguable whether it's illegal for you to access them)

undefined

hm I didn't thought about that, yet. Maybe I'll give it a try and see if I can find it there, if I find a site who do that

John Rennie

6:31 AM

@Akash.B Wikipedia gives this link

undefined

found it, thanks for the hint, Emilio

Akash. B

@JohnRennie what's this?

no abstract

John Rennie

@Akash.B it would be worth googling the title of the paper in acse there is a copy on the Internet somewhere. However it's quite an old paper so we might be out of luck.

Akash. B

@JohnRennie what that paper says?

John Rennie

@Akash.B aha, found a copy

Akash. B

6:42 AM

@JohnRennie its full of scientific terms!

John Rennie

... though that doesn't give an exact distance. It just says it's farther than 2.5 kiloparsecs away.

@Akash.B from a quick glance it looks as if they determined the distance by measuring the brightness and spectra of Cygnus X-1 and the stars around it.

It might be worth asking in the Astronomy SE. I must admit I don't know how the distance to stars like Cygnus X-1 is measured.

Akash. B

@JohnRennie how can i observe it?

cygnus X-1

John Rennie

There have been a few related questions but I don't see any on its distance.

Secret

8:13 AM

eventhorizontelescope.org/blog/…

Tonight that is

undefined

yeees, I'm waiting for that too

John Rennie

2 p.m. UK time. Annoyingly I'll be out this afternoon so I won't see it live.

But then, when you've seen one black hole you've seen them all :-)

undefined

maybe they all do look different :)

GPhys

10:16 AM

it's time to start combing arxiv for early preprint leaks

Secret

10:45 AM

Can't wait in the far future to see a black hole with a cube shaped event horizon to blow up the minds of everyone

PM 2Ring

@Secret Rudy Rucker's Infinity and the Mind*? That's a good book, but it's more oriented towards maths & philosophy. And it's over 30 years old, and there has been a lot of development in cosmology in that timespan. I love Rudy's work: I first read one of his early books about higher dimensional geometry and special relativity, before I discovered that he also writes scifi.

Secret

yeah I knew, I just make a note that that crazy guy who suggests oscillation and stuff is not one of a crazy kind, but a whole community of normal people

I was reading that book in order to deepen my understanding of infinity

(by crazy guy, I mean that user who asked that esoteric question in PSE)

PM 2Ring

His popsci physics is pretty good, but like all popsci writings accuracy may be sacrificed for the sake of an engaging easy to understand picture. So please don't take it as gospel. Also, he's a mathematician, not a physicist. And he does have a tendency to get into far-out territory that may not reflect mainstream views. ;)

Secret

Well, I don't think a physicist can really say much about the nature of infinity. We have yet to secure an object that looks like infinity

but I will keep that outlandish tendency of his in mind

PM 2Ring

11:01 AM

@Secret I doubt that anyone's written a better or more accessible book about the mathematics of infinity for the non-specialist. His PhD topic was about transfinite stuff. FWIW, he had a couple of phone conversations with Gödel, I think that's mentioned in the book.

Secret

That's fine for me, the maths people in the maths chat have already exposed me to the deep end of formal systems, so I should be more than ready to comprehend the concepts in his books

Emilio Pisanty

Dutch F-16 flies into its own bullets, scores self-inflicted hits

PM 2Ring

I figure that he's entitled to be a little unrigorous from time to time. ;) And he is a philosopher as well as a mathematician, programmer, and scifi author. And amateur painter. He's a descendant of the philosopher Hegel.

Secret

@EmilioPisanty How NOT to ride a jet

undefined

11:16 AM

"the aircraft could be unexpectedly reunited with its recently departed rounds" I laughed pretty hard

2

PM 2Ring

They wouldn't have that problem if they were shooting photons instead of bullets.

Secret

oh yeah, but then all that water vapor will dissipate all that laser output away

undefined

and photons are cute

PM 2Ring

@Akash.B Bear in mind that we have located many potential black hole candidates, but it's difficult to prove that they really are black holes. OTOH, with the best candidates, if they aren't actually black holes, they'd have to be something even weirder.

Also, we need a quantum gravity theory before we can fully model black holes correctly, although almost all the experts expect that current physics is sufficient to explain almost all of the external features of a BH, and we only need quantum gravity to model the core of BHs.

JMac

physics.stackexchange.com/questions/471698/… Does this look like homework to anyone else? It seems like someone went and downvoted the two answers and VTC'd as homework; but it doesn't look like they read the question IMO

PM 2Ring

11:27 AM

The main external feature of a BH that's currently a little shaky is Hawking radiation, which is the result of a semiclassical theory, so it may be abolished by a fully quantum theory of gravity.

@JMac It looks primarily conceptual to me. And I've noticed a recent increase to close vote as homework borderline questions that seem primarily conceptual, but which contain some working by the OP that's been posted to show their thoughts, and to demonstrate that it isn't a straight homework dump.

JMac

@PM2Ring I wouldn't even really care that much about the VTC. I'm more frustrated that someone went and downvoted me and Aaron's answers presumably because they saw it as homework. It's annoying because clearly both answers aren't doing someone's homework for them; which is what we want to discourage

PM 2Ring

I appreciate this site's strong homework policy, but I also feel that when an OP makes an effort, and we can help them present their post as a conceptual question then we should give them that assistance, rather than just automatically close voting.

Emilio Pisanty

@Secret just do it in regions where the air has a low water-vapour content

JMac

Yeah, exactly. If they copy and paste their homework I VTC without giving any input. If it seems like they are hung up on concepts, but worded the question in a way that doesn't really fit, I usually try to help

Emilio Pisanty

say, the surroundings of an aircraft carrier

luckily that tends to be pretty dry air, right?

Secret

11:35 AM

lol right

PM 2Ring

@JMac In many cases, I suspect that it's a cultural thing. They are teaching kids how to pass physics exams instead of teaching them how to think like a physicist. It's just like the situation Feynman discovered in Brazil, as I mentioned a month or so ago. chat.stackexchange.com/transcript/71?m=48923454#48923454

Luyw

12:04 PM

hey guys, quick question, does potential energy basically means work before it is done?

gravitational PE for example is mgh, if an object falls to the ground starting from a distance h relative to it, the work is mgh, hence while the object is still in the air at distance h, PE is mgh

PM 2Ring

12:19 PM

@Luyw You could put it that way. And in many cases, you could turn it around, and say it's work after it's done. Eg, to lift your object you need to do work equal to mgh on it. Then when the object falls it can do mgh of work.

This is how a grandfather clock is powered. When you wind the clock up, a weight is lifted. As the weight slowly falls, the released energy is used to maintain the swing of the clock's pendulum.

JMac

@PM2Ring Reminds me of what I've heard the mentality is for a lot of areas in China. They apparently don't care as much about plagiarism and stuff as they do about getting caught; which is pretty strange.

PM 2Ring

And of course a swinging pendulum converts energy back & forth between potential energy and kinetic energy.

@JMac Getting caught proves that you're not very good at playing the game. ;)

JMac

Playing the game at all shows you don't really care about scientific advancement or understanding; that's more the issue

Luyw

thank you @PM2Ring, but putting it the other way gives less meaning to the word "potential" as I see it

PM 2Ring

12:35 PM

The paradigm of the scientist vs the universe, pitting their mind against the laws of nature, is a fairly modern thing. For most of history, in most regions, the focus was on your position & power in society. Just think of the ancient astronomer-priests of Babylon.

Those guys made damn fine observations, and collected data for centuries that became the basis of Western astronomical tables for more than a millennium. But they were priests, and astrologers, and had strong influence on their society and its rulers.

China has a very long tradition of competitive exams. But not a long or strong tradition of the scientific method. I remember reading somewhere years ago that in China of a few centuries ago, the top public servant in charge of iron & steel production wasn't chosen by him demonstrating vast knowledge of the scientific properties of metals, or mining & refining techniques. He was the guy who could write the most pleasing poem about iron.

PM 2Ring

12:57 PM

We are certainly not immune to this problem in the West. Sure, people appreciate the power of science & technology. But great scientists and science teachers generally don't have a high place in society, and that's reflected in what they get paid. The famous ones almost invariably have some "human interest" angle going on, like Hawking with his motor neuron disease, or Feynman with his bongo playing, safe-cracking, and penchant for topless bars. ;)

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