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tommac
2008-Apr-17, 01:36 PM
Could Spagettification happen at the edges of the universe ( relative to us ) where the universe is receeding at the speed of light relative to us?

CodeSlinger
2008-Apr-17, 01:57 PM
First, the distance at which things appear to recede from us at the speed of light is defined as the Hubble radius. As I understand it, this radius is significantly smaller than the radius of the observable universe. At the edge of the observable universe, things appear to recede away from us at faster than the speed of light! (if we use co-moving distances)

To answer your question, think of it this way: for an observer located at the edge of our observable universe, it would appear to them that it is we who are receding away from them at great speeds. Are we being spaghettified?

tommac
2008-Apr-17, 02:05 PM
I dont know that is the question I am asking. From my understanding those being spaghettified dont realize that they are being spaghettified, in fact things are quite normal. So could we currently becoming spaghettified as we speak? I guess we would continuously be spaghettified relative to some galaxay somewhere right? We would be on the edge of a distant galaxies universe.

Hmmm however really we would have been spaghettified years ago. In any case ... what I am trying to get at is are there any other similarities between a black hole and the edge of our universe? The ones I thought of were :

1) the receeding of time greater than the speed of light
2) the emmission of radiation
3) (via the similarity of opposites ) Opposites in many ways density, size, gravity






First, the distance at which things appear to recede from us at the speed of light is defined as the Hubble radius. As I understand it, this radius is significantly smaller than the radius of the observable universe. At the edge of the observable universe, things appear to recede away from us at faster than the speed of light! (if we use co-moving distances)

To answer your question, think of it this way: for an observer located at the edge of our observable universe, it would appear to them that it is we who are receding away from them at great speeds. Are we being spaghettified?

CodeSlinger
2008-Apr-17, 02:28 PM
If we were being spaghettified, we would be VERY aware of it. Obviously, we are not being spaghettified right now. So what I was trying to point out to you was that since a distant observer measuring us to recede from them at great speeds does not cause us to become spaghettified, us measuring things (whether at the edge of our observable universe or elsewhere) to recede from us at great speeds would not cause them to become spaghettified either. More to the point, spaghettification of the kind you seem to be talking about, which occurs in the vicinity of blackholes, is an effect of the strong gravitational forces in that vicinity. It has nothing to do with the apparent speeds at which things recede from each other.

Are you, by chance, still trying to compare the Big Bang to a black hole? I was pretty sure that Chris Hillman had already explained to you that this is not a valid comparison. In fact, yes, he did right here (http://www.bautforum.com/questions-answers/72828-white-holes-red-shift.html#post1219183). With all due respect, how many times do you have to be told something is wrong before you let go of the idea? Did you look at the page he linked?

http://www.math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html

Occams Ghost
2008-Apr-17, 03:19 PM
No.

If you tried to pass the imaginary boundry of the universe, the matter you are composed of would rush away at the speed of light because of the infinite curvature.

CodeSlinger
2008-Apr-17, 03:31 PM
No.

If you tried to pass the imaginary boundry of the universe, the matter you are composed of would rush away at the speed of light because of the infinite curvature.

What???

tommac
2008-Apr-17, 03:39 PM
Firstly can you site an article about
spaghettification where it states that the thing being spaghettified knows it is being spaghettified? My understanding of it was that from the outside of a black hole things look like they are getting spaghettified and ripped apart and all of that stuff, but for the thing entering the black hole, it does not notice.


Secondly, The article below that you quote was when I was trying to compare the big bang to a white hole.

I am not trying to compare a black hole to the edge of the universe. This is much different dont you think?

The question I am asking is valid dont you think?

We have two cases:

1) a black hole whose space time is receeding away from us at the speed of light ... as something gets close it appears to be spaghettified because of the bending of space time at a very fast pace.

2) The edge of our universe, where space-time is also being warped ( relative to us ) at a very fast pace.

After thinking about this a while ... I believe that the same phenomenon would exist, however the big difference is that it would be much more evident near a black hole. For being close to the edge of the universe we are looking at a very large space-time ( the opposite IMO of a black hole ) so as the spaghettification happens it is much more obvious when focused on a point. I think that the effect would be slightly different ... instead of spaghettification you would have some sort of elastication ( I dont think that is a word ) which would be similar to spaghetification in the direction of the edge of the universe ... BUT instead of stretching towards a point ... you would stretch towards an infinite x,y,z ( like a cone??? or a sphere?? ) and the effect would not be as sudden and would only be obvious on very large objects. Say you had a super giant ... maybe 1,000,000 ( not smart enough to do the math here ) light years long. If he was going feet first into the edge of the universe ( where it receeds at the speed of light ) ... his feet would slowly get much larger than his head ... this included stretching his height towards the edge but at the same time the feet would stretch to infinite size at the point of the event horizon.

OK ... what happens when a black hole reaches a point relative to us, where it is receeding at the speed of light away from us? You would have both massive contraction of space time and massive expansion of space time. Would the singularity of the black hole expand?






If we were being spaghettified, we would be VERY aware of it. Obviously, we are not being spaghettified right now. So what I was trying to point out to you was that since a distant observer measuring us to recede from them at great speeds does not cause us to become spaghettified, us measuring things (whether at the edge of our observable universe or elsewhere) to recede from us at great speeds would not cause them to become spaghettified either. More to the point, spaghettification of the kind you seem to be talking about, which occurs in the vicinity of blackholes, is an effect of the strong gravitational forces in that vicinity. It has nothing to do with the apparent speeds at which things recede from each other.

Are you, by chance, still trying to compare the Big Bang to a black hole? I was pretty sure that Chris Hillman had already explained to you that this is not a valid comparison. In fact, yes, he did right here (http://www.bautforum.com/questions-answers/72828-white-holes-red-shift.html#post1219183). With all due respect, how many times do you have to be told something is wrong before you let go of the idea? Did you look at the page he linked?

http://www.math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html

John Mendenhall
2008-Apr-17, 04:10 PM
There is no attainable 'edge' of the universe. No matter where you are, the universe looks the same.

Neverfly
2008-Apr-17, 04:21 PM
What???

Insert ATM tab here;)

CodeSlinger
2008-Apr-17, 04:23 PM
Firstly can you site an article about spaghettification where it states that the thing being spaghettified knows it is being spaghettified? My understanding of it was that from the outside of a black hole things look like they are getting spaghettified and ripped apart and all of that stuff, but for the thing entering the black hole, it does not notice.

The very definition of spaghettification is something getting torn apart, because the parts closer to a blackhole experiences a stronger gravitational pull than the parts further away. An outside observer may or may not observe the victim getting spaghettified, depending on whether the spaghettification occurs inside or outside the event horizon. But for the victim, spaghettification is very real, very measurable, and very final.

http://archive.ncsa.uiuc.edu/Cyberia/NumRel/BlackHoleJourney.html

http://en.wikipedia.org/wiki/Spaghettification (I imagine Chris would've cringed at this one)


1) a black hole whose space time is receeding away from us at the speed of light ... as something gets close it appears to be spaghettified because of the bending of space time at a very fast pace.

As I mentioned above, as something approaches a blackhole, it doesn't just appear to be spaghettified, it is spaghetiffied.


2) The edge of our universe, where space-time is also being warped ( relative to us ) at a very fast pace.

No, the spacetime at the edge of our observable universe is NOT being warped!

You're trying to see how various concepts fit together. That's great, but without an understanding of the underlying mathematics, you can waste a lot of time doing this without getting anywhere. Verbal/textual descriptions are only vague, crude approximations, and trying to fit them together without knowing how the underlying mathematical models work will only result in a lot of misconceptions and incorrect conclusions. Please stop speculating, and start reading. Channeling Chris Hillman once again, you might start with the resources he told you about here (http://www.bautforum.com/questions-answers/72828-white-holes-red-shift-2.html#post1219680).

tommac
2008-Apr-17, 04:25 PM
No.

If you tried to pass the imaginary boundry of the universe, the matter you are composed of would rush away at the speed of light because of the infinite curvature.

Ummm ... isnt that similar to spagettification? Also not sure if it was here or on another thread ... I realize that the distance needs to be scaled ... So the spagettification would not be as obvious ...

If I were a super giant ( many light years in height ) going feet first into the edge then my feet would be swept first and be expanded to infinite size while my head was still normal ( for a super giant ) ....

tommac
2008-Apr-17, 04:27 PM
As I mentioned above, as something approaches a blackhole, it doesn't just appear to be spaghettified, it is spaghetiffied.

I disagree!!! Please provide the math.

CodeSlinger
2008-Apr-17, 04:33 PM
No, I'm done answering your questions, which can be answered with just a little effort on your part. Start reading please.

Neverfly
2008-Apr-17, 04:36 PM
Does it seem to you that Q&A is getting ATM again?:confused:

I have this sinking feeling...:doh:

cjl
2008-Apr-17, 04:51 PM
I disagree!!! Please provide the math.

Sure. Gravity is determined by GM1M2/R2

So, if you are fairly close to a smallish black hole, R is smaller for your feet than for your head, and therefore they are pulled in faster than your head is. This causes spaghettification. For a 1 solar mass black hole, you get an event horizon of around 8km radius. If you happened to be 10km away from the black hole, your feet would be accelerated at 1.3542*10^11 gees towards the black hole. Your head, 6 feet farther away (roughly) would be accelerated at 1.3538*10^11 gees, a difference of 0.0004*10^11 (4*10^7) gees. Your feet would be trying to accelerate into the black hole 40 million gees faster than your head, stretching you apart.

tommac
2008-Apr-17, 05:14 PM
Sure. Gravity is determined by GM1M2/R2

So, if you are fairly close to a smallish black hole, R is smaller for your feet than for your head, and therefore they are pulled in faster than your head is. This causes spaghettification. For a 1 solar mass black hole, you get an event horizon of around 8km radius. If you happened to be 10km away from the black hole, your feet would be accelerated at 1.3542*10^11 gees towards the black hole. Your head, 6 feet farther away (roughly) would be accelerated at 1.3538*10^11 gees, a difference of 0.0004*10^11 (4*10^7) gees. Your feet would be trying to accelerate into the black hole 40 million gees faster than your head, stretching you apart.



Thanks ...
I realized that this effect would happen soon after I posted. I think the effect is still there but it is very different when expanding into infinity rather than collapsing into a singularity.

On a grand scale for a supersized giant ( many light years tall ) going feet first into the horizon ... the feet would begin to expand to infinity, while stretching towards the horizon ... One of the biggest differences is that collapsing to a point would create a conical ( possibly wrong here ) shape with a max diameter of the head or sholders ... and a min diameter of 0 ( or near 0 ) and there would be a stretch towards the singularity. For the effect when being pulled out to infinity ... the cone would have a minimum diameter of the head of the giant and stretch out to a cone of infinite diameter ( or near it ) at the feet while doing a similar stretching.

loglo
2008-Apr-17, 06:46 PM
) The edge of our universe, where space-time is also being warped ( relative to us ) at a very fast pace.

Tommac,
I think you are mixing up General and Special Relativity. They are not the same thing. Just because the expansion of the universe is whisking something away at light speed or greater does not mean that Special Relativistic affects like time dilation apply.

mugaliens
2008-Apr-17, 07:44 PM
Spaghettification occurs in very strong gravity gradients relation to local dimensions, such as near the event horizon of a black hole. While the edge of the universe may be receding from us close (or at) the speed of light, it's doing so due to expansion.

Locally, there, there is no spaghettification.

Things seem as normal there as they do here.

tommac
2008-Apr-17, 08:06 PM
Tommac,
I think you are mixing up General and Special Relativity. They are not the same thing. Just because the expansion of the universe is whisking something away at light speed or greater does not mean that Special Relativistic affects like time dilation apply.

So time dialation is mass based only?

tommac
2008-Apr-17, 08:07 PM
I think things would seem normal to something being Spaghettified just externally it appears to be ripped apart


Spaghettification occurs in very strong gravity gradients relation to local dimensions, such as near the event horizon of a black hole. While the edge of the universe may be receding from us close (or at) the speed of light, it's doing so due to expansion.

Locally, there, there is no spaghettification.

Things seem as normal there as they do here.

Hornblower
2008-Apr-17, 09:58 PM
I think things would seem normal to something being Spaghettified just externally it appears to be ripped apart
Please try to show us, mathematically, why you think that is so.

Moonhead
2008-Apr-18, 03:52 PM
Please try to show us, mathematically, why you think that is so.

In a non-math way, I think Tommac (erroneously) conceptualizes spaghettification as something applying to the 'canvas' of space, so to speak... Like a portion of space and everything in it, is bend, stretched, twisted, whatever, as a whole - so the forces of nature that apply to the stuff in that portion, also apply through the same bend, stretched, twisted ways, sorta neutralizing the deformation, undoing it locally.

Like, when you play a 3:4 movie on a 1:2 screen, things are deformed. But it doesn't matter to the people in the movie, because the oval wheels on their cars run smooth anyway. Something like that, I suppose.

tommac
2008-Apr-18, 06:39 PM
Please try to show us, mathematically, why you think that is so.

Again ... I dont speak math well ... so let me explain what I think in english.

Gravity is a warpng of space-time ... things without gravity are travelling in a straight line and gravity warps one side of space so that things appear to fall towards the bending area. As we would fall into a black hole, we would not mention a difference is the flow of our time, nor the compression of our space. We would fall towards an object but would not get torn apart.

However from something far away things would appear quite differntly ... It would appear due to the bending of space-time and possibly due to the frame dragging ( rotating black hole ??? ) that wierd things are happening ... as time slows drastically and space compresses. Who knows maybe our particles in our body appear to get torn into their molecular pieces ... But meanwhile we just continue to fall ... I am not sure what would happen after the even horizon near the singularity ... maybe we fall forever like zeno ( fixed my spelling ) the warrior princess. Or maybe we are shot out into another place. From the point of our universe anything that is falling into a black hole has no future.

Demigrog
2008-Apr-18, 07:11 PM
There is no attainable 'edge' of the universe. No matter where you are, the universe looks the same.

I think this needs to be repeated. :) Speculating what happens at the edge of the universe is a bit premature if there is no actual edge of the universe.

tommac
2008-Apr-18, 07:26 PM
I think this needs to be repeated. :) Speculating what happens at the edge of the universe is a bit premature if there is no actual edge of the universe.

in my posts I have been using edge of the universe to mean ( and I think I defined it early on ) as the point at which the universe is expanding at the speed of light RELATIVE TO US.

Hornblower
2008-Apr-18, 11:16 PM
Again ... I dont speak math well ... so let me explain what I think in english.

Gravity is a warpng of space-time ... things without gravity are travelling in a straight line and gravity warps one side of space so that things appear to fall towards the bending area. As we would fall into a black hole, we would not mention a difference is the flow of our time, nor the compression of our space. We would fall towards an object but would not get torn apart.

However from something far away things would appear quite differntly ... It would appear due to the bending of space-time and possibly due to the frame dragging ( rotating black hole ??? ) that wierd things are happening ... as time slows drastically and space compresses. Who knows maybe our particles in our body appear to get torn into their molecular pieces ... But meanwhile we just continue to fall ... I am not sure what would happen after the even horizon near the singularity ... maybe we fall forever like zeno ( fixed my spelling ) the warrior princess. Or maybe we are shot out into another place. From the point of our universe anything that is falling into a black hole has no future.
Yikes! That is not even good English, let alone good physics. It is difficult to discern what you are thinking from this latest batch of words that somewhat resemble plain English, but are plagued by moments of poor syntax and/or choice of words. Case in point:
As we would fall into a black hole, we would not mention a difference is the flow of our time, nor the compression of our space.

Let's do a thought experiment in which our planet has been compressed into a black hole, for which the event horizon is about the size of a golf ball. A 1-meter steel rod is placed about 60 meters away from the black hole and aligned with it, and then allowed to fall freely toward it. At this distance, 1/100,000 of Earth's actual radius, the overall gravity is 10 billion times stronger than our familiar gravity. The difference in gravitational acceleration between the leading and trailing ends of the rod is given by the formula:

Δa = 2aΔr/r

where r is the distance to the black hole and Δr is the length of the rod. In this case Δa is about a/30, or over 300 million g's. That means the leading end is attempting to drag the trailing end at that rate, and the cohesive force needed to do so will vastly exceed the tensile strength of any steel.

A much milder example of this phenomenon actually happened to Comet Shoemaker/Levy during its initial flyby of Jupiter, a couple of years before the crash. It was torn asunder and the fragments were strung out like a string of pearls. They converged somewhat as they receded, but were strung out all over again during the final plunge. Had the comet been more nearly like a ball of pasta dough, it might have been stretched into something resembling a strand of spaghetti before breaking up; hence the expression "spaghettification". I am confident in my opinion that this was a very real tearing up of the comet, not merely an illusion as seen from afar.

Our best theoretical inferences about the cosmos indicate that the conditions at the edge of the observable zone are much like those right here, with no extreme gravitational gradients except locally around dense objects, just as around here. What sort of observations of what type of objects give you the illusion of an object undergoing spaghettification?

seanhogge
2008-Apr-18, 11:19 PM
But if you were to go there, you'd see it's not an edge at all, it only seems like one when you back away. Or am I missing something?

Hornblower
2008-Apr-18, 11:32 PM
But if you were to go there, you'd see it's not an edge at all, it only seems like one when you back away. Or am I missing something?
To the best of my knowledge you are missing nothing, and basically have it right.

loglo
2008-Apr-18, 11:41 PM
So time dialation is mass based only?

This has been very well answered in mugalians' post in your other thread about black holes.

JohnD
2008-Apr-19, 09:38 PM
"Could Spagettification happen also at the edge of the universe? "

As His Noodly Goodness extends from end to end of this Universe, of course it is spaghettified.
Nhoj

tommac
2008-Apr-20, 02:17 AM
um ... thanks for the english lesson .. .

Now your 60 meters is relative to what? The thing is that the black hole at that close at that much gravity space-time would be very compressed ...

so from an external source it would definitely look like we were being crushed

g is in m / s2 right? but as space-time is compressed wouldnt the force be different? Although I may eventually agree with you here ... as we are lighter on the moon than on earth we would be lighter on earth than near a black hole. However I still think that the warping of space-time would definitely make things from appear differently from the thing entering into the black hole than when watching it from a distance.



Yikes! That is not even good English, let alone good physics. It is difficult to discern what you are thinking from this latest batch of words that somewhat resemble plain English, but are plagued by moments of poor syntax and/or choice of words. Case in point:

Let's do a thought experiment in which our planet has been compressed into a black hole, for which the event horizon is about the size of a golf ball. A 1-meter steel rod is placed about 60 meters away from the black hole and aligned with it, and then allowed to fall freely toward it. At this distance, 1/100,000 of Earth's actual radius, the overall gravity is 10 billion times stronger than our familiar gravity. The difference in gravitational acceleration between the leading and trailing ends of the rod is given by the formula:

Δa = 2aΔr/r

where r is the distance to the black hole and Δr is the length of the rod. In this case Δa is about a/30, or over 300 million g's. That means the leading end is attempting to drag the trailing end at that rate, and the cohesive force needed to do so will vastly exceed the tensile strength of any steel.

A much milder example of this phenomenon actually happened to Comet Shoemaker/Levy during its initial flyby of Jupiter, a couple of years before the crash. It was torn asunder and the fragments were strung out like a string of pearls. They converged somewhat as they receded, but were strung out all over again during the final plunge. Had the comet been more nearly like a ball of pasta dough, it might have been stretched into something resembling a strand of spaghetti before breaking up; hence the expression "spaghettification". I am confident in my opinion that this was a very real tearing up of the comet, not merely an illusion as seen from afar.

Our best theoretical inferences about the cosmos indicate that the conditions at the edge of the observable zone are much like those right here, with no extreme gravitational gradients except locally around dense objects, just as around here. What sort of observations of what type of objects give you the illusion of an object undergoing spaghettification?

Hornblower
2008-Apr-20, 11:54 AM
um ... thanks for the english lesson .. .

Now your 60 meters is relative to what? The thing is that the black hole at that close at that much gravity space-time would be very compressed ...
My analysis was rough-and-dirty Newtonian mechanics. I don't know how much different the numbers would be in a rigorous Einsteinian treatment, but since you have acknowledged that you do not know much about the math at that level I see no great value in belaboring it. I don't think the fundamental phenomenon of gravity-gradient-induced stretching would go away. We would have a space/time warp whose magnitude would change a lot over a relatively short distance.

so from an external source it would definitely look like we were being crushed
Now, some rough-and-dirty relativity. If an object's velocity is approaching c, as would be the case near the event horizon of a black hole, a remote observer would see it as compressed along the direction of the motion, if my 40-year-old recall of my college days is correct. That is opposite the direction of the actual stretch that occurs in a severe gravitational gradient, such as that which shredded the aforementioned comet. In that case the relativistic effects were negligible.

I don't know how much the relativistic effects would distort our view of my steel rod as it falls toward the Earth-mass black hole whose Schwarzschild radius is roughly that of a golf ball. The rod is still over a thousand times farther away. If anyone out there who is up to speed on the necessary math wishes to contribute to this discussion, please enlighten us.


g is in m / s2 right? but as space-time is compressed wouldnt the force be different? Although I may eventually agree with you here ... as we are lighter on the moon than on earth we would be lighter on earth than near a black hole.
You appear to be concurring with my analysis here. If we were 6000 km from my black hole the gravity would be indistinguishable from what we experience on Planet Earth. When we move in to 60 meters, it increases by a factor of billions and has a severe gradient over a distance of 1 meter.

However I still think that the warping of space-time would definitely make things from appear differently from the thing entering into the black hole than when watching it from a distance.
And I never argued otherwise. That is a separate issue from the question of whether or not spaghettification actually occurs at a particular location.

Occams Ghost
2008-Apr-20, 03:16 PM
Bottom line is, is that you can't pass any boundary of the universe, because itr doesn't have one. Everything is self-contained, so it does us no good to talk about what is outside the universe, because it would imply a boundary between something and something else. In this case, there is no boundary.

tommac
2008-Apr-21, 02:22 PM
Whoa whoa whoa OG ... So are you saying that there is no boundary moving into a black hole? Is entering into a black hole similiar to viewing a distant galaxy moving away from us then? To them we are moving away ... To something falling into a black hole the rest of the universe is changing???





Bottom line is, is that you can't pass any boundary of the universe, because itr doesn't have one. Everything is self-contained, so it does us no good to talk about what is outside the universe, because it would imply a boundary between something and something else. In this case, there is no boundary.

Occams Ghost
2008-Apr-21, 02:53 PM
Be careful here. The no-boundry proposal is very shakey at best. A black hole does has a boundary, but again, the universe is self-contained, and nothing can move into a boundary of a black hole. As soon as one did try this, they would be scrambled up and spat back out. It's almost as if the universe wants to keep everything safe within its own arena.

Occams Ghost
2008-Apr-21, 02:54 PM
So with your example of something moving into a black hole is partially incorrect, since nothing can.