# Black holes, White Holes and Baby Universes:

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Aug 13, 2013.

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What can I say????

Get a life!!!

3. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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What if spaghetti fell into the black hole?

5. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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Same here! Except with me it's when the 40th person in a post quotes the 2nd. Grrrrrrr................

7. ### Magical RealistValued Senior Member

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delete

Last edited: Sep 26, 2013
8. ### Boris2Valued Senior Member

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well....a number 8 would become a number 1, for a start.

9. ### wegsMatter & Pixie DustValued Senior Member

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lol

I needed a laugh...

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11. ### brucepValued Senior Member

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Since you folks have been discussing the 'spagettification' process I'll add these interesting details derived from the Schwarzschild metric of GR.

If you were falling feet first towards the singularity at r=0 you would feel a spagettifacation, from head to toe, equal to g_earth at

r_ouch = (2Mdr/g_earth)^1/3

This is in geometric units where M is the mass of the black hole in unit L [m, a solar mass =1477m], dr=your length from head to toe in unit L [m], g_earth=1.09E-16 unit L-1 [m^-1]. So r_ouch varies with M and dr [much less]. It turns out that the proper wristwatch time only varies with dr so for a constant dr [your length before spagettification] dTau_ouch is the same for any mass black hole.

dTau_ouch=2/3(dr/g_earth)^1/2

For the derivation it's just the derivative of

dr/dTau=-(2M/r)^1/2 = g_rain = M/r^2 and then the derivative of g_rain = (2M/r^3)dr

From there it's just some simple algebra to get r_ouch and dTau_ouch using a specific dr and g_earth [9.8m/s^2=1.09E-16m^-1].

12. ### wegsMatter & Pixie DustValued Senior Member

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Thanks for this, brucep!

I regret reading about "spaghettification" when I did. I can't get it out of my mind, now. The author of one particular article said it would most likely be slow and eventually agonizing. Snapping in half at our weakest body point, around our waist/hips. This might be a dumb thought, but I was surprised that we would experience or process pain in the same way as we do on earth.

13. ### brucepValued Senior Member

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There was a question associated with the r_ouch and dTau_ouch equations in a text I was reading. The question was [paraphrased]: Would a blackholenaut feel pain before they were completely 'spagettified' at r=0? The idea was a blackholenaut would begin feeling pain when tidal acceleration between 'head and toe' was equivalent to g_earth. Would knowledge of the pain reach the brain before complete 'spagettification'? For me it works out to be .12719s. So my answer was 'no'. LOL. This stuff is really esoteric but 'physic fun'. Doing a bunch of math to figure out what would happen if you fell into a black hole.

Messed that up it would be .29117s. What do you think does the pain have time to reach your brain before complete 'spagettification'?

14. ### quinnsongValued Senior Member

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How long does it take to form a thought like,I am in pain?

15. ### wegsMatter & Pixie DustValued Senior Member

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yes it's great (and twisted) fun, indeed.

So, your answer was 'no.' Interesting. I've been fascinated with black holes and tend to read a lot about them, over the years. That is just so strange to me that we wouldn't feel pain (knowledge of pain hitting the brain, but isn't that the same thing?) before the tidal forces exceeded the elastic limits of our bodies. I don't get it because once the body reaches ''complete'' spaghettification, you're a goner by that point. lol I'm a lay(woman) so, just trying to make sense of why our brains wouldn't have knowledge of pain until we're almost dead.

This is a super cool article, take a look when you can.

http://earthsky.org/space/astronomers-see-gas-cloud-sweep-past-milky-ways-central-black-hole

16. ### brucepValued Senior Member

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I don't know but I bet somebody does? I just guessed that I'd be dead before the pain registered in my brain.

17. ### brucepValued Senior Member

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I wrote a long post but the restore function 'didn't work' after I posted to quinnsong. ?. Always makes me want to scream. Anyway dTau_ouch is ~.29117...s proper wristwatch time for all r_ouch. Regardless the mass of the black hole. This is for all r/M.

dTau_2 - dTau_1 = (2/3M)^1/2 (r^3/2_1 - r^3/2_2)

Thanks for the link. The following NASA link discusses the 'dying pulse train' discovered in the HST data archive by Joseph Dolan and research team. The 'cloud in your link' will provide further evidence as it falls into the black hole. At the NASA site they have HST photos of a star being torn apart as it falls towards the event horizon of a black hole.
Question just for fun.
Why is the star 'torn apart by tidal forces outside the hole' while you and I, and the Earth, wouldn't be? Probably not always but generally.
Black Hole Caught Red-handed in a Stellar Homicide
http://hubblesite.org/newscenter/archive/releases/exotic/2012/18/image/a/
'Death Spiral' Around a Black Hole Yields Tantalizing Evidence of an Event Horizon
http://hubblesite.org/newscenter/archive/releases/exotic/black-hole/2001/03/text/
Reenactment of the spacetime event confirming the prediction by GR
http://imgsrc.hubblesite.org/hu/db/videos/hs-2001-03-a-low_mpeg.mpg

The dying pulse train is a GR predicted observation made by the remote Schwarzschild bookkeeper. Another term for the dying pulse train is 'wink out'.

Last edited: Sep 28, 2013
18. ### wegsMatter & Pixie DustValued Senior Member

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haha yes, I groan when that happens, too. Did this happen on your phone? If so, nothing you can do there, but if it happened using your laptop...you can always copy the text you've typed out, sign back in...and then, paste for your reply. I'm assuming you knew this, but if not...that's a good work around.

Ok, regardless of the mass. I've read that the mass of bh does play a role in the effects of spaghettification.

huh. we wouldn't meet the same demise as a star?

I've aways ''thought'' that if a black hole has a mass of a few times our sun let's say, we would be destroyed, (spaghettification) before we reached the horizon. However, if you fell into a much larger black hole, with a far greater mass than that, you would reach the horizon without difficulty. So, moral of the story is if you want to see the inside of a bh, choose a HUGE one. lol

19. ### Boris2Valued Senior Member

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larger difference in the tidal forces across such a large body as a star compared to a planet or human. same reason we have tides on earth but the water in our bodies doesn't slop around. guess.

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A star [or planet] is a huge amount of mass, and if it happens to get caught up with, or is apart of a system, where another partner has become a BH, it would probably obtain an orbit around the BH at 3 Schwarzchild radius....this parameter is the inner most part of any stable orbit around a BH....
The gaseous outer atmosphere of the star would see its mass gradually spiral into the BH and beyond, while the main part of the star kept orbiting.....In other words, a BH is not really a gluttonious ravourness feeder...It just keeps sucking in gradually consuming all the star over time in the end

A human body, or a probe for that matter sent towards the BH, could suffer from spaghetification before it reached the EH.....
In fact at 1.5 Schwarzchild radius is what we call the photon sphere, where light/photons can orbit...eg, If you maintain some stability at this orbit, and shone a torch directly ahead, your vision would see the back of your head as the light/photons orbited and encountered your head.

By the same token a SMBH, as we have at the galactic center, could see you enter and not be torn or stretched until you were much closer to the Singularity....

21. ### wegsMatter & Pixie DustValued Senior Member

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Thanks Boris & paddoboy for the info!

22. ### brucepValued Senior Member

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For different M [different mass black holes] the distance from r_ouch to r=0 varies. dTau_ouch doesn't vary because the rate dr/dTau [proper velocity] varies over the path 'r_ouch to r=0' so that dTau_ouch remains the same. So that brings us to another interesting prediction of GR using Schwarzschild coordinates. The average proper velocity from r=2M [Schwarzschild event horizon] to r=0 [center of the black hole] is 3/2c. Everybody knows that GR can't make predictions about quantum phenomena so for the real singularity at r=0 we can 'get around' the infinity for the purpose of mapping the path dr/dTau to r=0. This is done by integrating the 2nd component of the metric so division by zero is no longer a problem. That was just 'A bit' about using GR to speculate about the spacetime inside the black hole. Excluding the singularity at r=0 which is the domain of quantum gravity. So now a knew query: if the blackholenaut measures the local speed of light, at any point along the path from r=2M to r=0, [a local direct measurement] is the blackholenaut going faster than the light being measured? We can also evaluate the natural path of light after being emitted from the head and toes of the blackholenaut. One thing you can do to have fun with this is make a black hole so big that it would take a 'year' in the local proper frame of the blackholenaut to fall from r=2M to r=0. I made a thirty year black hole that was probably > the observable universe. Build a black hole so big that g outside the event horizon is equivalent to g_earth. GR text are always centered around evaluating predictions for the weak and strong fields. Really interesting science and fun. Completely esoteric fun. I'm looking forward to the movie 'gravity'.

23. ### brucepValued Senior Member

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Never thought of that. I was getting at the delta between the electromagnetic force and the gravitational force of nature. We could probably figure out what delta g across the star [in the radial direction] would signal the stars beginning 'spagettification'. LOL. Magnificent HST photos. Having such a wonderful tool is awesome. I live about a 40 minute ride to the top of palomar mountain. I used to take my Celestron up there until it became to much of a hassle spotting with my huge reading vision delta. The rode ends at the entrance to the observatory. Two roads: one to the observatory parking lot and one to 'someplace' that requires a cattle crossing over the road. I set up and just started trying to find M-13 when there was a 'big' rustling in the bushes behind me [and the scope]. I was gone in the proverbial 'new york second' to 'behind my truck' about 10 yards away. Out came a huge cow which deftly avoided crushing my scope. It was completely dark but I could see the outline of the 'darker' cow. LOL. Scared the crap out of me. The cow took off up the road with the cattle crossing.