Talk:Spaghettification/Archive 1

Archive 1

Untitled

(William M. Connolley 17:33, 5 Sep 2004 (UTC)) This page might benefit from a link to Image:Tidal-forces-calculated.png.

Who's got a picture of an astronaut being spaghettified?? 204.52.215.99 15:12, 28 March 2007 (UTC)

I'm sorry about making seemingly irrational changes and saying it was not needed; in my browser there has recently been a change meaning that the images are placed neatly below each other at all times. I thought this was a welcomed new wikipeida feature. [[User:Sverdrup|❝Sverdrup❞]] 20:14, 6 Sep 2004 (UTC)

They line up neatly for me too. Perhaps it's a browser issue?(firefox 0.9.3). Mind you even if it is, it's clearly better to go with Bryan so that it looks good for everyone. Theresa Knott (Nate the Stork) 20:25, 6 Sep 2004 (UTC)

Ah, I see. I'm using Mozilla 1.8a1 with the "Classic" Wikipedia skin, if you're curious. I would also welcome a new Wikipedia feature like that. :) Bryan 20:27, 6 Sep 2004 (UTC)

Sure of it?

Eventually, close to the singularity, they become large enough to tear atoms apart. -Anon

You make a good point. No come to think of it I'm not sure. I've reworded the text. Theresa Knott (The torn steak) 12:26, 17 Oct 2004 (UTC)

Accelerated Towards?

Gravity is fixed acceleration. Even going down a black holes throat. The space/frames of refrence are going to elongate, and light is going to slow down to the outside observe.

but the acceleration due to gravity is the same. Due to the acceleration, your velocity increases, and due to the velocity increase, as you go faster, your distance down the hole increases.

This is all that happened when the Apple fell from the tree.

Which theory of gravity are you working with?

Artoftransformation 17:15, 9 November 2005 (UTC)

I spent a while pondering your comment, trying to think of a way to ask exactly what you're talking about without sounding patronizing. I couldn't think of one, sorry. What are you talking about, specifically?

This doesn't have to bring in time dilation or relativistic velocity or anything silly at all, this is basic physics alone. Of course at any specific distance, gravitational acceleration is fixed, but that's really the entire point. You don't usually notice tidal forces (our ocean being an obvious exception), this is just an extreme case since black holes are relatively small so the differences in acceleration are magnified, and relatively huge stuff gets sucked into them.

Example: Pick up a ball bearing and drop it, it falls at ~9.8m/s^2 because you're standing around 6000km away from the center of the Earth. Get a really tall ladder and drop another ball bearing from 3000km above the surface of the earth, and it only falls at 4.9m/s^2. Now, take a 3000km-long foam noodle, hold it by one end so the bottom end is a few hundred meters above the Earth's surface, and drop it. Ignoring air resistance, what happens? After the first second, the bottom end has fallen 4.9 meters, while the top end has fallen 2.45; it stretches out to compensate for this difference. Earth's gravity might not even be sufficiently strong for the sake of this example - pretend there's a big metal ball at both the top and bottom ends, whatever. The point is that with black holes, you don't need to use foam rubber; their high mass/density by definition means that there's going to be enough free space to fall in for the tidal forces to become strong enough to rip nearly anything apart (ie. tidal force drops off much faster than gravitational force, and we start running into dirt and stuff by the time we get within 6000km or so of the center of the Earth's mass).

Just as a totally trivial, but at least possible, example (physics is not my forte), take a black hole of a thousand solar masses. Its Schwarzschild radius is 2952m, so pretend we're somehow hovering (100000m-2952m) above it, and that we're 2m tall. Get out of your still-hovering spaceship and fall. Yeah, it'll only take you 1.226x10^-4 sec to splatter, but in that time, based only on the original disparity in acceleration due to the difference in distance of your head and feet, your head will have fallen 4m less than your feet. Of course this also assumes you're basically a person-shaped pile of dust, but with this sort of force (stretching 4 meters in 100 microseconds), I don't imagine the human body would put up much resistance at all. In reality you'd be stretched much farther, due both to your height becoming more relatively significant compared to the decreasing distance, and your absolute height increasing the entire time you fell.

The second component of spaghettification has nothing to do with tidal force per se - like the article's top diagram shows, if you have something that is wide (not difficult when you drop a star into a black hole that's a few km across), its edges will be pushed together, moreso at the bottom, because their definition of "down" is different. I don't know if this would normally work fast enough to push the top and bottom apart from each other, but it'd at least make the object thinner. Straker 11:39, 11 November 2005 (UTC)

Whoops. Okay, so my quick example obviously entails going FTL. Sillily enough, this doesn't break anything in the concept of spaghettification itself, so if this happens to bother you, play with the numbers some (a thousand solar masses is kind of a weird mass anyways, should usually be much heavier or much lighter). Straker 12:10, 12 November 2005 (UTC)

Can't spaghettification be explained much more simply?

It looks to me like this article is overcomplicated and spaghettification can be explained in under 30 lines, plus possibly 1 very simple diagram (using Newtonian gravity):

• Gravitational pull is inversely proportional to the square of distance.
• So the pull on the near side of an object is greater than the pull on the far side.
• That means the near side wants to accelerate faster than the far side towards the source of the gravity field.
• This difference in acceleration creates tension between the 2 sides of the object. The tension is proportional to 2 factors: the length of the object in the direction pointing towards the gravity source; the strength of the gravitational force.
• For "normal" gravity fields, like Earth's, the effect is negligible if the object is smaller than a large asteroid. But in an extremely strong gravity fields, such as a black hole's, the tension can become enough to stretch the object and eventually pull it apart.
• Spaghettification contains a positive feedback loop - as the "victim" gets longer, the tensile force increases, etc.
• If the gravity source is very small (e.g. black hole) and the "victim" is relatively large, the stretching is increased by lateral compression since the sides of the "victim" are falling along converging paths. If the lateral compression actually increases the "victim's" length, it also increases the tensile force, etc.

Or am I missing something?

If I'm right and the article can be simplified, we can use the extra space for additional aspects, e.g.: any new features added by general relativity; spahettification eventually destroys atoms and even sub-atomic particles falling into black holes, because as the distance from the black hole decreases the gravitational pull increases very fast (inverse square law) and the difference in distance between the leading and trailing edges of the "victim" becomes a large fraction of the distance to the black hole; what happens when 2 black holes meet.Philcha 18:55, 16 March 2007 (UTC)

could it be explained as like the shape of a rain drop?

An upside-down raindrop, maybe. 76.185.61.24 (talk) 05:53, 20 October 2009 (UTC)

Does the "tidal forces" diagram help non-specialist readers?

I doubt whether the diagram "tidal forces acting on a spherical body in a gravitational field" helps non-specialist readers. To understand it I think readers would need to understand (a) the basic principles of tidal forces; (b) how to split forces into components and re-combine them; (c) the convention that length of arrow is proportional to strength of force.Philcha 13:30, 28 March 2007 (UTC)

Should the article mention another kind of spaghettification?

The process where a computer program turns to spaghetti code. Interestingly enough, it is also an indication that the program is falling into a black hole. (It didn't look like there was an appropriate place to mention this in the article though.) —The preceding unsigned comment was added by EmptyString (talk • contribs) on 22:54, 19 April 2007.

I've added a disambiguation message about this. --Christopher Thomas 23:01, 19 April 2007 (UTC)

How about a "complex math analysis" or something?

You know, something involving general relativity, calculus, tensors, the works. Practically every other astrophysics, quantum physics, and physics article in general delves into the enormously complex math behind it, so why not this one? :) -Matt 01:26, 19 June 2007 (UTC)

My math isn't good enough! More importantly, how many readers would it help? People who understand general relativity, calculus, tensors, the works don't look up subjects like Spaghettification in Wikipedia.Philcha 02:28, 27 June 2007 (UTC)

Remove "tidal forces" diagram?

A while ago I wrote in this Talk page: "I doubt whether the diagram "tidal forces acting on a spherical body in a gravitational field" helps non-specialist readers. To understand it I think readers would need to understand (a) the basic principles of tidal forces; (b) how to split forces into components and re-combine them; (c) the convention that length of arrow is proportional to strength of force." Nobody has argued in favour of keeping the diagram. I also note that the diagram's caption contains a serious error, because the source page for the image says that the gravity source is (counter-intuitively) to the right. I propose to remove the diagram.Philcha 23:44, 13 July 2007 (UTC)

Just fixed two of the four issues right now. The other two (splitting forces and general understanding of tidal forces) are probably a bit much to completely explain in an image caption, but we do have a separate article on tidal forces and there's an image farther down in the article that IMO dovetails well with this one on explaining where the compression and stretching comes from. I think it's a keeper, myself. Though perhaps we should rotate it to match the vertical orientation of the other image, having gravity acting vertically is more intuitive. Bryan Derksen 01:10, 14 July 2007 (UTC)

The diagram as shown actually has two sources of gravity, one on the right and one on the left. This is different from spaghettification, in which only one source of gravity is present. This diagram would fit nicely in a tidal forces article, but not so well in this one. My vote is for removal of this diagram from this page. 142.103.207.10 (talk) 23:35, 4 December 2008 (UTC)

No, only one source of gravity - that's the strange thing about tidal forces. The tidal force is the difference between the gravitational pull on the far and near ends. Because the far end is subject to a weaker pull than the near end, it accelerates more slowly, and the object stretches. --Philcha (talk) 10:34, 20 December 2008 (UTC)

Good catch. The diagram is obvious nonsense. I have finally removed it and replaced it with a correct one with a caption pointing to the relevant article. DVdm (talk) 11:21, 20 December 2008 (UTC)

Thanks, DVdm. The new diagram is clearer, but I still don't think it's the best choice for this article. The diagram still shows two sources of gravity (one on either side of the object). It does a good job of illustrating tidal forces, but it's not accurate for this article, which is on spaghettification. Spaghettification only involves one source of gravity. I like the other diagram better, the one with the four green balls falling towards the brownish planet. That should be the primary diagram for this article because I think it best illustrates the subject of this article. 142.103.207.10 (talk) 22:01, 31 December 2008 (UTC)

Actually the diagram does not show, but assumes only one source, which is either on the right side or on the left side of the planet (see diagram caption). The gravity of the planet itself is of less importance: it merely plays the role of "shaping agent", trying to keep the planet spherical against the tidal forces caused by the single other mass, which tries to "spagettify" the shape of the planet. A similar thing happens with a small spaceship, for which the "shaping agent" is the whole of the electric forces between its atoms. The tidal forces of a nearby neutron star will try to spagettify it in exactly the same way. See the article on tidal forces. Hope this helps... - Cheers and happy 2009. DVdm (talk) 10:38, 1 January 2009 (UTC)

Tidal forces are a pair of forces acting upon object b given another object B of mass M at distance d. The force tends to stretch b along the common axis between b and B, proportional to M and r, the "radius" (assuming b is a sphere) of b along the axis between b and B, and inversely proportional to d cubed. Note that the tides and tidal forces on b do not depend on any motion of b relative to B, and don't depend on the mass of b, nor the size of B (it may be considered a point mass). Naturally, B will have its own tidal forces caused by b. SkoreKeep (talk) 23:24, 9 June 2011 (UTC)

The problem is that the caption says "Longer arrows indicate stronger forces." but actually the arrows show the difference between the force acting at the point on the circumference versus the mean force which acts on the centre of mass. What it should show is a "triangle of forces" at each point with a single arrow on the centre to show that the present arrows are the vector sum. However, I doubt that would make it more understandable so perhaps a correction to the caption would be simpler. George Dishman (talk) 11:06, 19 February 2015 (UTC)

another reference

Found this comment in the article, but it seemed more appropriate here. Gamaliel (talk) 20:30, 28 February 2008 (UTC)

(Another reference is needed here, for the word was popularized and put into the public mind via a Discovery Channel program on black holes around 2001, in which a physicist graphically described the term)

Orbital Spaghettification?

I'm a bit concerned about the section at the bottom titled 'Orbital Spaghettification'. I can't put my finger on it, but there're shades of OR in there. Not helped by its apparent lack of cites. Can anyone confirm the statements made? - Taskis (talk) 08:15, 28 June 2008 (UTC)

• AIUI, spaghettification (in the black hole sense) is only experienced when you are aimed right down the gravitational well. When you pass close by in a highly elliptical orbit, you might pass closer than your Roche limit and be disrupted. The two are different because in one, you are in free-fall, experiencing ONLY tidal forces, but in the other, you are in an orbit. Disruption is indeed due to tidal forces, but this is not spaghettification. I'm wiping it. Sword (talk) 02:55, 30 June 2008 (UTC)

Since a black hole has no solid surface

Are you sure? I never heard about that, so at least you may provide some reference for this strangeness. —Preceding unsigned comment added by 83.103.38.68 (talk) 12:07, 17 July 2008 (UTC)

We're sure that black holes have no solid surface. They missed their last opportunity to have one when they collapsed to singularity. No forces in the universe were strong enough to hold the surface up, and it fell in. 76.185.61.24 (talk) 05:55, 20 October 2009 (UTC)

To clarify, the black hole is the space inside the event horizon, not just the singularity at its center. Everything between the singularity and event horizon is (expected to be) void, since anything that crosses the event horizon will eventually merge with the singularity. 173.85.41.215 (talk) 08:50, 23 March 2010 (UTC)

Really? The space between the singularity and the event horizon contains infalling matter. The fact that it cannot ever get out again because it has passed the event horizon makes no difference; in fact, the EH is just a mathematical figure, sensible only from the outside, and an infalling object probably has no sensible indication it has passed within it. The spaces inside and outside are continuous; curved, but smoothly continuous in the gravity field right up to the singularity. The fact that we cannot see into the event horizon doesn't say anything about what is in there, just that it cannot ever come out. SkoreKeep (talk) 23:12, 9 June 2011 (UTC)

Frame drag

Linear frame dragging should also increase the 'spaghettification' effect in the region of superdense objects, beyond that of just the difference in gravitational force varying by distance. This should probably be mentioned somewhere in the article (and linear frame dragging expanded upon in the fram-dragging page). 173.85.41.215 (talk) 08:55, 23 March 2010 (UTC)

Error in math?

The assertion that tidal forces approach infinite at some point other than the event horizon seems to not make sense to me. The article writer clearly states that for ultra-large black holes, the tidal forces approach infinite past the event horizon. Isn't the whole point of the event horizon that it is the point at which the effects of gravity make it impossible for light to escape? To do that, isn't it already necessary that the curvature of space-time be infinite at the event horizon? What lies beyond could be quantum foam, a singularity, <insert theory>, but the gravity well isn't going to get any steeper past the event horizon.

The fact that the event horizon isn't a "physical barrier" doesn't make it any less real. Dilation effects on time and distance approach infinite as one approaches it, so getting past it is as difficult as penetrating any tangible barrier.

Beerslurpy (talk) 17:17, 22 August 2010 (UTC)

This is not per se related to dilation effects. It is well "known" (i.e. it can be shown) that one can cross the event horizon of a supermassive black hole without feeling any effect of tidal forces. I have a added two sources for this. The calculation is done (in a very accessible way) in Taylor and Wheeler's Exploring black holes. DVdm (talk) 17:58, 22 August 2010 (UTC)

Question

"The point at which tidal forces destroy an object or kill a person depends on the black hole's size. For a supermassive black hole, such as those found at a galaxy's center, this point lies within the event horizon, so an astronaut may cross the event horizon without noticing any squashing and pulling, although it.." My question is if this is correct. Whether an object is destroyed is different from whether an object undergoes strain. Why wouldn't an astronaut notice changes before tidal forces become lethal? Or has some calculation made that for supermassive black holes, the tidal forces are typically that small? What if the astronaut brought a sensitive instrument with him?76.218.104.120 (talk) 21:28, 9 October 2013 (UTC)

See a detailed calculation in Taylor and Wheeler's Exploring Black Holes: Introduction to General Relativity. Here we're supposed to discuss the article, not the subject. You might try the wp:reference desk/science. Good luck. - DVdm (talk) 06:50, 10 October 2013 (UTC)

My issue IS with the article.I don't think the statement should be in there, it's imprecise, for one thing.76.218.104.120 (talk) 00:07, 21 October 2013 (UTC)

It is properly sourced. What would you change to make it more precise, and which source do you have to support that change? - DVdm (talk) 04:55, 21 October 2013 (UTC)

Event horizons applicable only to ballistic trajectories

Briefly explaining the reason for restoring my edit noting an exception to "once you're inside the event horizon you can't excape"...

The event horizon at the Schwarzschild radius of a black hole is a mathematical structure, not a physical one, and applies only to ballistic trajectories. For supermassive black holes where the tidal forces at the Schwarzschild radius are negligible, it is entirely possible for a spacecraft to cross back and forth over the event horizon if it has a source of thrust greater than the local gravitational gradient.

Of course, you'd need a torchship to entirely leave the Hill sphere of a supermassive black hole. But generally speaking, the "unless you have a source of thrust" disclaimer is applicable to any discussion of ballistic trajectories.

152.120.255.251 (talk) 18:30, 24 April 2014 (UTC)

Claiming the above edit. Physicsandwhiskey (talk) 18:35, 24 April 2014 (UTC)

User:DVdm cites http://books.google.be/books?id=5dryXCWR7EIC&pg=PA265, the classic example of an astronaut undergoing spaghettification. There's certainly nothing wrong with this illustration, but this clearly describes a ballistic infalling trajectory. The event horizon of a sufficiently large black hole is no barrier to a ship with thrust. Physicsandwhiskey (talk) 18:52, 24 April 2014 (UTC)

Check the cited source: http://books.google.be/books?id=5dryXCWR7EIC&pg=PA265. It doesn't say anything about upward thrust. Once inside the horizon, there is no way out, not even with "upward thrust". If you want to add something like this to what the source says, you will need a wp:reliable source per our policy wp:original research. Please have a careful look at (and read of) these policy articles. - DVdm (talk) 18:53, 24 April 2014 (UTC)

Of course it doesn't say anything about thrust because a ballistic infalling trajectory undergoes only gravitational acceleration. Your assertion that no object can escape the event horizon of a black hole even with thrust is certainly not supported by your source, and is in fact flatly incorrect. The local gradient g of the gravitational field at a black hole has no lower bound; a sufficently large supermassive black hole can have a gravitational acceleration at its event horizon lower than that of Earth. Your source doesn't support what you're claiming. Physicsandwhiskey (talk) 19:02, 24 April 2014 (UTC)

But I don't claim it in the article. I claim it here on the talk page to explain, even though I shouldn't have to do that. We are not allowed to discuss the subject here. We can only discuss what goes in or out the article—see wp:talk page guidelines. We don't need sources for what we claim here on talk. We do however need sources for challenged content in the article. See wp:BURDEN. And it's upon you - DVdm (talk) 19:09, 24 April 2014 (UTC)

"event horizon of a sufficiently large black hole is no barrier" You might want to check out Surface gravity#Surface gravity of a black hole: "the acceleration of a test body at the event horizon of a black hole turns out to be infinite in relativity". If ships could escape black holes, so could light, which would render the whole notion of black hole meaningless. AS DVdm said, you'll need a rock solid source for this claim. Paradoctor (talk) 19:56, 24 April 2014 (UTC)

I doubt there's any source specifically stating "an astronaut with thrusters could leave the event horizon of a sufficiently black hole" any more than there's a source specifically stating "it's possible to play guitar on Mars", but the math isn't complicated. A supermassive black hole of 600 million solar masses (give or take) would have a Schwarzschild radius of a little over 1 AU and a "surface gravity" lower than that of Earth. Any rocket with enough thrust to lift off under its own weight on Earth would be able to hover at the event horizon, dip below it, or leave it.

The event horizon of a black hole is defined with respect to infinity, not with respect to local spacetime; there is no local uniqueness in the curvature of space at the event horizon. You cannot observe that you are crossing the event horizon; wherever you are, there is simply a "new" event horizon farther below you corresponding to the distance for which escape velocity exceeds lightspeed. The event horizon is not an inescapable barrier; it is simply the point from which no ballistic trajectory can escape to infinity. Physicsandwhiskey (talk) 13:39, 25 April 2014 (UTC)

See wp:NOR and wp:CALC: "Routine calculations do not count as original research, provided there is consensus among editors that the result of the calculation is obvious, correct, and a meaningful reflection of the sources." Without such sources to support what you have in mind, we're not allowed to discuss this—see wp:talk page guidelines. Continuing to do so would be disruptive. - DVdm (talk) 15:52, 25 April 2014 (UTC)

Yes, this would be wp:CALC. The sources are simple: here's the equation for the size of an event horizon (R_s = 2GM/c²), here's the equation for surface gravity (g = GM/R²), and for an example, the largest known supermassive black hole is 21 billion solar masses, or around 4.2e40 kg. I trust none of those are disputed. :) Given that G = 6.67e-11 in SI units and c = 3e8 m/s, the Schwarzschild radius of NGC 4889 is 6.27e13 m. Using the above euqation for surface gravity gives us a gravitational acceleration of 712.6 m/s², about 72 gees. Quite a bit of acceleration to be sure, but not insurmountable; an F-1 rocket engine has a thrust-to-weight ratio of 94 and SpaceX's Merlin 1D has a ratio of 160. Seems pretty straightforward to me. (note: I was doing the math in my head before and thus underestimated the surface gravity in my prior comment; sorry about that) Physicsandwhiskey (talk) 16:46, 25 April 2014 (UTC)

It would not be wp:CALC. Read about sources here. And please have a careful read of wp:no original research. You are wasting (y)our time. - DVdm (talk) 16:54, 25 April 2014 (UTC)

It's not WP:CALC for the simple reason that you don't have consensus that your calculation is correct. DVdm and I deny categorically the correctness of your calculation. Your formula for surface gravity is not correct. I repeat the quote from above: "the acceleration of a test body at the event horizon of a black hole turns out to be infinite in relativity". The formula you refer to is only valid in Newtonian gravitation, and fails miserably around black holes. You're wrong, and there is no way you can get this in the article. This is because it contradicts the very definition of black hole: "A black hole is defined as a region of spacetime from which gravity prevents anything, including light, from escaping." Paradoctor (talk) 17:26, 25 April 2014 (UTC)

... and even if his formula would correct, we couldn't discuss it here, let alone put it in the article. This not the place to educate each other, again and still per wp:TPG. - DVdm (talk) 17:32, 25 April 2014 (UTC)

Fair enough. It seemed a simple fix, but hey, maybe I'm wrong; it's been a while since I did much of anything with relativity. I'll swing back by here if I happen to come across a clear source. Cheers! Physicsandwhiskey (talk) 17:52, 25 April 2014 (UTC)

That's the spirit—and how Wikipedia works . Cheers - DVdm (talk) 17:58, 25 April 2014 (UTC)

Aye, I remember. I was a contributor back when I was a YEC, years ago. Physicsandwhiskey (talk) 18:52, 25 April 2014 (UTC)

Discrepancy in the "simple example" equation

The main page says $F={\frac {\mu lm}{4r^{3}}}$ but this NASA page seems to differ by a factor of 8 giving $a={\frac {2GMd}{r^{3}}}$ which is equivalent to $F={\frac {2\mu lm}{r^{3}}}$ : Black Holes and Tidal Forces. Can someone confirm which is correct.

Also, since the preceding diagram shows unconnected point particles, would it not be more useful to have an equation giving the separation as a function of the change of height and then a separate diagram showing how the tension in a rope acts on the ends to cancel the tidal force before giving this equation? George Dishman (talk) 11:38, 19 February 2015 (UTC)

Why Spaghettification Does Not Occur by Ann Hall Kitzmiller

The article above purports to mathematically demonstrate that the concept of spaghettification doesn't reflect reality. Could someone more qualified than I please review it and comment? It's at http://dynamicspacetime.com/ Thanks! — Preceding unsigned comment added by 198.236.58.30 (talk) 22:30, 28 April 2015 (UTC)

Please sign your talk page messages with four tildes (~~~~). Thanks.

That is not a wp:reliable source (in the Wikipedia sense), so we cannot use that here. Therefore we also cannot discuss it here—see wp:talk page guidelines. Cheers. - DVdm (talk) 06:31, 29 April 2015 (UTC)

Known

One of the notes on the bottom says, “The smallest black hole that can be formed by natural processes at the current stage of the universe has over twice the mass of the Sun.” I would change “natural processes” to “known natural processes”; after all, given that we may never know all the laws of physics, there is a chance that someone will discover a mechanism that will produce an even smaller black hole.--Solomonfromfinland (talk) 23:47, 27 April 2016 (UTC)

Sure, but that is always the case with every scientific statement—by definition of science (but of course excluding logic and mathematics as sciences). There is a chance that someone will discover a mechanism that will produce light that goes twice as fast as what is currently known as the invariant local speed of light. That's how science works. The word "known" could be added in zillions of other places. Adding it here might even induce a wp:POVvish tone, like "hey, but I think that there can be smaller ones, if we look harder..." - DVdm (talk) 08:26, 28 April 2016 (UTC)