md65536

Sorry, I was wrong. You are correct. http://www.newton.de...05/phy05139.htm My reasoning is bad because the ramp doesn't just provide an upward force that counteracts gravity (preventing the ball from accelerating at free-fall speeds), it also provides a horizontal force that causes the ball to accelerate horizontally too. It seems that the composition of these two force components will act normal to the ramp?, which for a ball will make a line between the point of contact and the ball's center of mass. This removes any "off-balance" force that could cause the ball to tip. However I don't think the same reasoning applies to a square block in general, if the block could be positioned with a corner (single point of contact) against the ramp, which could be done so that the normal force doesn't intersect the center of the block, then the normal force could provide some rolling torque to the block. In the typical starting case (probably also a stable state if the block was allowed to slide indefinitely), with the edge of the block flat against the ramp, any amount roll would cause one of the corners to become a "pivot point" which would tip the block back toward "flat against the ramp", so I guess even if it started off-balance on a corner then a rolling angular velocity couldn't accumulate for long or something, and would instead oscillate while approaching 0? Just like a block that is off-balance on a horizontal surface will roll, but only so much that it will rock back and forth and settle into a state with 0 roll. A block that is flat against the ramp will not be off-balance, no matter what the angle of the ramp is, because the force acting on the block and ramp is normal to the ramp.

You cut a piece out of the brownie and didn't even align to the edges and you're hoping to not suffer her anger? Here's the only idea I could think of:

On an incline steeper than 45 degrees, a square shape (as in a side view like the diagram's) will always be off-balance, and I believe should always tip over even while it's sliding, so it should develop a rolling angular momentum even though it is sliding frictionlessly. For steeper inclines: The rate of acceleration of tipping or roll would approach 0 as the acceleration approached g, which would (only?) happen if the angle of the ramp approached 90 degrees. Anyway the rolling momentum would be very little on a short ramp as in the example, especially with a square shape starting flat against the ramp. On any incline a ball should be always off-balance. If there's no friction then the ball's roll should have no effect on its linear movement (the movement could be entirely described as sliding even if it is also rolling). If we replace the ball with a square, and then replace the ramp with stairs, we should be able to describe setups where a block still slides down the stairs, or where it only tips and rolls down the stairs (and slides too?, maybe necessarily), or where it doesn't move at all. Sorry, this is getting further off topic... I think it's interesting but it doesn't make a difference to the puzzle.

The line is a world line. It's a line through two dimensions (on a 2d diagram at least). One represents time, the other represents... space! It is not a line through time, it is a line through spacetime. No, the object doesn't remain at its past coordinates, it moves through both space and time. What remains at past spacetime coordinates is "events", including if you will the event of "being" at a certain location at a certain time. The moon of some moment in 1969 was at some location and that event is fixed there and then. We are certain of this to the degree that we are certain of our understanding of applicable aspects of spacetime and reality etc. To say that the world line "develops" along one dimension and "changes" along another dimension, makes me think that you may have some additional assumptions that are getting in the way of understanding this. I don't think I understand it enough myself, or can explain it any better than has already been explained in this thread, but perhaps someone else can. I think the confusion comes from assuming something more than what was said, so there may be some important bit of information that is missing in these explanations which you are filling in with incorrect assumptions?? The moon, an object, usually refers to a ball of mass as it exists in one specific place and time. The moon described by its world line, something that "is" in all the places its ever been, is not an "object" that has an existence in reality as we know it. The world line is fixed in the 4d spacetime manifold. It only "develops" from the perspective of one who sweeps a plane along the time dimension... which essentially corresponds to our perception of the 4d spacetime manifold. When you view a spacetime diagram, you can look at the whole thing at once. But the way you would experience it in reality is not as a 2d diagram (experiencing it all at once) but as a line that sweeps along the time dimension. If this is confusing it's probably because I don't know the right words or even the right understanding!

I would paraphrase it thusly: Given that the moon "occupies" some given 4d spacetime coordinates... For space: At another time, the moon might not occupy that same space. For time: At another location, the moon does not occupy that other location at the same time. When you're talking about the moon moving away, you're talking about another time. If you're talking about one specific value for time, then the moon has a fixed spatial location for that fixed time. Sorry, I don't seem to be understanding what you're saying.

No, it doesn't make sense to say "the coordinate is empty". An event happens at a particular place and time (a 4d point on the spacetime manifold) and that point is fixed in 4d. It doesn't change. See http://www.scienceforums.net/topic/59951-inflation-and-causality/page__view__findpost__p__627339 The spatial coordinate can become "empty" as the object that used to be there moves away (so XYZ="where the moon was in 1969", T="2011" could be "empty"), but the spacetime coordinates of an event such as those involving the moon landing, will always be associated with those events. As I've already mentioned (#39), we know things about the past and the future, to varying degrees of certainty, due to physical laws, and we also know things about the past to varying degrees of certainty, due to memory (which also involves physical laws, allowing information to propagate through confined locations or something). Our conviction comes from our level of certainty of available information and of the physical laws. I'm not sure if the question is "Since we can't directly see the spatially near, temporally distant past, ... ... how do we know it hasn't changed?" -- The answer is that the spacetime manifold is fixed. Or, ... how are we certain that it happened as we say it did?" -- We are very very certain of the laws that connect those past events to current events, and of the directly visible information that is causally connected to those events (photographs, millions of human memories, etc). We're not that certain of everything. We know the solar system formed, and it contains clues about how it formed (ie "memories"), and we can observe other systems forming (visible accretion discs) and consider it likely that ours formed the same way that others did (due to "physical laws"). So we think specific events happened in the past, many of which we're not that certain of.

My take on this: F: To say that the height the ball will reach after reaching its minimum is 3m assumes that the ball is perfectly elastic and there is no loss of energy anywhere, which I don't think falls under the umbrella of "excluding any friction". However the elasticity etc is not specified, and the "maximum" height is asked for, so I think it's fair to assume best-case conditions of no loss for "maximum possible height". Technically, the question doesn't even specify that the "max height" is only after reaching its minimum, and the ball is already at 3m at the start so its max height cannot be any less than that. C: Typically a ball will roll down the incline and acquire angular momentum, which might allow it to roll up the incline after hitting the "wall". To see this effect, roll a rubber ball along the floor against a flat wall, and the ball can bounce with some vertical component to its velocity. Without knowing the properties of the ball etc it would be impossible to calculate C. However, this doesn't apply to the puzzle because it relies on friction in order to convert the ball's angular momentum into linear momentum. Excluding all friction, the ball would slide down the incline, but it would also roll (I think) because the downward gravitational force is the same throughout the volume of the ball but the upward force of the plane is off-center, allowing the ball to constantly keep tipping faster off balance as it slides down. This is beside the point of the puzzle though.

I think it will be "less logical", or at least have less correspondence to a "common sense" understanding of reality. My idea of what a ToE will look like is "Emergence", where the other theories you mention are emergent aspects of some more-fundamental description of the universe, of which we only see and experience emergent aspects. Gravity, particles, geometry etc would all be emergent. What I don't have a guess about is whether we would be able to figure out "the absolute fundamental nature" of the universe, or if it might be possible that any more-fundamental model of the universe that we could describe could itself be emergent from some other model. I think that any such fundamental models could be described mathematically, so I doubt that all of math could be emergent. Perhaps I'll start a new thread before I ramble off topic...

Don't Gödel's incompleteness theorems imply that this is impossible? Wouldn't such an equation have to transcend the set of all mathematical equations? http://en.wikipedia.org/wiki/G%C3%B6del's_incompleteness_theorems I can't imagine anything like what you're talking about, where it must be simple enough that "cursory glances" show meaningful things, yet complex enough to describe everything. So I'm curious about your motivation for writing it. Is it just an idea you're imagining, or is it based on a real equation (or even the hint of one)? If the latter then I'm interested in what your perception of gravity is, and why it would make you think that everything mathematical can be deduced from it. My opinion is one of doubt, but also puzzlement.

No. It's not really a tornado. It freezes them and encases them in ice (it kills everything that gets stuck in the ice, not everything that touches the outside, as can be seen in the video where starfish are crawling over it). I don't think it has anything to do with difference in pressure. This is curious and I want to guess at what's happening here. I don't know for sure though. Guesses: - As saltwater contacts the cold air, it is cooled enough to be able to freeze. The ice that forms from saltwater is purer water (less salty) than the water it froze out of. This means that this very cold saltwater is essentially separated into less-salty ice, and more-salty water, both of which are at temperatures low enough to freeze ice out of the (normal-salty) water. The cold, saltier brine is able to remain as liquid because it is extra salty! - The saltier brine is heavier and sinks into the surrounding seawater. Because it is so cold, it is able to freeze ice out of the surrounding (less-salty) water. This creates a tube through which it can flow. - The tube grows and eventually reaches the bottom. At that point, the extra-salty cold brine flows along the sea floor. It is essentially a freezing cold liquid being poured through a less-cold liquid. Anything that has the cold liquid being poured over it can become frozen, and anything that has ice form around it can become trapped in the ice.

The difference is that if you say the words "time dilation" you are reifying time, by making "something" of "it". What is "it" that dilates?, one might reasonably ask. When you use the words "event duration of physical processes dilation", you are simply describing that durations become longer in certain circumstances. It's easy to see that durations can "become stretched out" without having to "be something" that can be stretched out. But with the word "time"... uh... Well see, they're just different, because they're different words. I know it doesn't make any sense when I say it, but owl will explain this all much better than I can.

Well, it made sense when it was on wikipedia. Nah, it still doesn't make sense to me but your previous post makes me see where my error is.

If clocks appear to slow down, doesn't that mean that the "Event Duration of Physical Processes" has lengthened? (That is, the processes involved in say one revolution of a clock hand, take longer duration to complete.)

Observable universe: "In Big Bang cosmology, the observable universe consists of the galaxies and other matter that we can in principle observe from Earth in the present day, because light (or other signals) from those objects has had time to reach us since the beginning of the cosmological expansion. [...] the current comoving distance to the edge of the observable universe is calculated to be 14.3 billion parsecs (about 46.6 billion light years) [...] The age of the universe is about 13.75 billion years, but due to the expansion of space we are observing objects that were originally much closer but are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the comoving distance at the present time) than a static 13.75 billion light-years distance." [http://en.wikipedia.org/wiki/Observable_universe] I started replying to your post, but then I found everything I was writing in the "Misconceptions" section of the above link. My previous posts have contained misconceptions too! "Distances obtained as the speed of light multiplied by a cosmological time interval have no direct physical significance." -- Sounds like light cones are not the right tool. The wikipedia article should provide some answers. I need to shut up and do some learnin! This is where I was confused, thanks.

A specific light cone is relative to an observational frame of reference (the spacetime point that is the apex of the cone being maybe the most important thing, as least in simple examples???). Events that lie on any specific cone are fixed spacetime points that don't move. Objects move but events don't... only the events remain on the surface of the light cone (whose apex is also a fixed spacetime point, because we're talking about the lightcone of an observer in a single instant), but... the object, extended in time, and described by its world line... is uh... It's not that "an object is fixed to a light cone", it's that its world line always intersects that light cone (for stuff in our spacetime vicinity at least, on the order of billions of years and light years), so there is always an instant where the object (or a past state of the object, one might say) can be observed "on any given light cone". We can gather information about stuff that's not on the surface of a light cone, because of "physical laws". We can use the current observed state of a system and understand previous states that must have preceded it, and we can predict future states to varying degrees of certainty, because the progression of states follows certain laws. One might say that the observable state of a system contains "memory" of previous events. Things are the way they are due to causal relationships that precede observable events. So if we see a nebula, its current state encodes much information of say the star that created it. We observe systems that have memories, and the observer systems can have memories too, where information can oscillate for long periods of time and intersect with many many many different light cones through time. I think you might be talking about extending light cones through time, such as describing "Everything that I see in a day". That's not a light cone. A light cone is a 3D surface in a 4D space. If extended through time I think it becomes a 4D volume that is a subspace of the 4d space. Or, there is the 4D volume that is contained by the past light cone of a single observational instant, which includes everything I see now and everything I could have ever seen and everything that causally affected everything I see or could ever have seen. This is also a 4D subspace.

Quote from the link: "- Distance is defined as the spatial separation at a common time. It makes no sense to talk about the difference in spatial positions of a distant galaxy seen 9.1 billion years ago and the Milky Way now when galaxies are moving. - The Universe is homogeneous and isotropic, so it has no edge. Thus there cannot be a maximum distance. Distances greater than speed of light times the age of the Universe are commonplace. But a uniform grid in the Universe shown at left below is very non-uniform when plotted using the light travel time distance" This doesn't make sense to me. What's the point of talking about the distance between the Milky Way and a galaxy that you can only see as it was 9.1 billion years ago? Sure, you can predict its "true distance right now", but that won't have any effect on us whatsoever for over 9 billion years. There is no causal connection between "us, now" and "that galaxy, now". We see it 9.1 billion LY away, as it was when we are seeing it. What's the point of taking something that we observe, and saying "Well it's not actually there, it's moved. And, it's not actually *that*, it's evolved for 9 billion years so it'll probably be quite different (most of its stars will probably die by then anyway)." I don't see how you could consider what you're talking about as being the same thing as what you observe. -- That can be a philosophical issue but I'm just wondering what the practical point of considering the "current" predicted distance to an observed object is. If you were planning on sending a signal to it, then maybe its distance now is relevant.

I've seen conflicting information. This video: claims that it can't be molten aluminum but shows an experiment where aluminum at the supposed temperatures of the fire is seen glowing as it's poured! At this point I would have to do further research before continuing to claim that there is anything I know to be scientifically impossible in the NIST report. I hope others will continue to bring scientific arguments to this discussion. What's sad is that evidence provided for both sides tells just enough to support a claim, and nothing further, with no room for uncertainty. Anything more is either left out, not worth investigating, etc. The best evidence I've seen so far involves one side trying to prove a point while the evidence they're presenting shows something else, because that something else is just pure evidence, not pre-interpreted evidence presented only to support the interpretation. Another Feynman quote: "The only way to have real success in science, the field I’m familiar with, is to describe the evidence very carefully without regard to the way you feel it should be. If you have a theory, you must try to explain what’s good and what’s bad about it equally. In science, you learn a kind of standard integrity and honesty."

The first part sounds good but is beyond me. It's the reason for the expected "heat death" end of the universe. The second part must be correct. If we can receive a signal from the "intermediate" which has received a signal from the "disconnected", then there must have been time enough to receive a signal from the "disconnected" which means it's not actually causally disconnected. Disclaimer: I'm trying to figure this out as I go and I have no idea about the credibility of the link I quote below. I suppose we can get mixed up on the meaning of "visible universe". I googled to find out the distance to CMB and found this answer: "[...] the today distance to the matter which emitted the light we are now getting as CMB. It says 45.65 billion LY, but you can round that off to 45 or 46. OK strictly speaking that is not the 'distance to the CMB'. The distance to the CMB is zero, it is all around us. It is radiation and some of it is in this room. 46 billion LY is the distance to the MATTER that emitted the CMB radiation that we are currently receiving. Technically, 46 billion LY is called the distance to the 'surface of last scattering'." [marcus, http://www.physicsfo...p/t-280981.html] But now I've confused myself. If the age of the universe is about 14B years, then we cannot see (now) anything beyond 14B LY because it would require more than 14B years for that light to reach us. Therefore I think the causally connected observable universe must be at most 14B LY. HOWEVER, 14B LY is the spatial distance to the event of the "last scattering" of some material, and that material would have kept traveling away from us. Some of that material may now be say 16B LY away???? and may become visible in a few billion years. Other material may be say 30B LY away and moving away faster than the speed of light so it will never be visible to us. Also, since apparently the rate of expansion is increasing, the 23-34B LY boundary should get closer in the future! I think that this means that the currently observable universe is within 14B LY. The causally connected universe extending to 23-24B LY is not currently visible, but events within that range can become visible in the future (but, for events around that range, not until the universe is at least 23B years old). Also... as the age of the universe grows, while the distance to the "causal boundary" or whatever decreases, at some point these two values should be equal. At that point, I think what happens is that the material that gave off the CMB radiation we're then seeing, will quickly be moving away faster than the speed of light???, and the CMB radiation will be the last we'll see of that material! After that point, we should not be able to detect CMB radiation any more.

Sounds alright. I think others would be able to improve that description (better than what I could do). I would say: Everything we observe -- every observation -- can be considered an "event", such as "Neil on Earth", "Neil in space at t=5000", "Neil in space at t=5001" etc. Some of those events can be outside our (Houston's) light cone, such as "Neil on the moon right now", but those same events will be on the past light cone of ours in the near future (about a second in the future in this case). So I would disagree with "he navigates the past light cone of Houston". However, yes, his world line will always intersect with any of our past light cones, so he is always observable. He navigates the spatial realm of Houston's past light cone, but just outside of it in the temporal dimension, as does pretty much everything (according to SR). When you say "he", if you mean him as an object extended through the time dimension, then his spacetime location(s) can be described with his world line, which always intersects with Houston's light cone. If by "he" you mean him existing in different specific single instants (which could be called events), then there will be instants that are on the light cones of Houston's specific instants, and others that are not. The event of him touching down on the surface of the moon is an instant that is only observable in an instant at Houston. But, for any light cone of Houston's, there will be an event corresponding to "Neil intersecting the surface of that light cone". Either way, some "he" is always theoretically observable to Houston. There is probably a simpler way to say this than what I wrote.

Alright, I will agree with you that simpler explanations are better. I will also say that a LOT of stuff happened that day, and just like the rest of life there's going to be some very unlikely things happening mixed in with all the likely things. If something seems unlikely (like WTC 7 collapsing due to heat expanding a specific beam and weakening others), that doesn't mean it couldn't have happened that way. If we debunk all of the "scientific" claims against the official explanation, then we should be left with the "likelihood" of the official explanation, and that might give us some high or low degree of confidence in the explanation, but unless it was statistically impossible I can't really say "It couldn't have happened that way." However, an explanation that relies on scientific impossibilities is a complication, not a simplification. Claiming that the molten metal is aluminum is a complication, because molten aluminum does not glow as seen in the videos. An explanation I've come across in some of the videos is that it was molten aluminum well-mixed with burning office materials. This is a complication because office materials don't mix with aluminum. They float on top. A simple explanation for the molten metal is that it is steel melted with thermate. There are complications with this too, including that there was no evidence of thermate found. However this has a simple explanation too! "NIST simply never checked for the presence of thermite or thermate" [http://en.wikipedia....piracy_theories] The simple explanation for why they never checked is: "NIST did not test for explosive compound residue in steel samples, stating the potential for inconclusive results, and noting that similar compounds would have been present during construction of the towers," [same ref as above], or "When asked why NIST did not test for explosive residues, NIST spokesman Michael Newman responded that NIST saw 'no evidence saying to go that way.'" [http://en.wikipedia....ld_Trade_Center] Saying that there was no thermate in the wreckage because none was found and nobody looked for it, is like saying that length-contraction doesn't happen at human scales because no one has done an experiment that can confirm it. If the likelihood of thermate is low (negligible, as NIST implies), then it currently falls under "Unlikely, but not impossible". If the glow of the dripping molten metal can't be explained, then "it is molten aluminum" falls under "not possible." The case for thermate can be considered even less likely, if there's an alternative explanation that is scientifically possible.

I'm not sure what you're saying here. Do you mean the theories are elaborate, or that they tend to be far-reaching (ie. involving a lot of conspirators)? I suppose that if we have a lack of understanding of a situation, and think that we can fill in the details with guesses and assumptions, then it's easy to grow a conspiracy theory. It will probably have holes in it, so if you keep filling the holes with guesses it can get pretty complicated. Any theory built on layers of conjectures is probably pretty bad. That goes both ways though... as soon as you put together a few assumptions like "The government has no reason to lie so they wouldn't; it would take thousands of conspirators to pull off something like this; it would be impossible for anyone to have access to the buildings before 9/11" etc, the theory can become unreliable. Also, what do you mean by "easier"? I don't think it's easy to say that something that is not scientifically possible actually happened.

The Loose Change link reminds me of something else. The Iraq war lie was exposed but I don't remember anyone facing any consequences for the lie. Clinton was impeached for lying about sex. A large percentage (I remember ~35% but the first link on Google says 84%! http://www.prisonplanet.com/articles/October2006/141006poll.htm) of people think that 9/11 was a lie, among them both experts and lay people. That proves nothing about whether or not they're right, but it does show that exposing the lies doesn't necessarily mean that anything will be done about it. This wasn't kept secret for a decade. People know about it. People demand answers, and are ignored. I'd also like to speculate on ways that the conspiracy could have been pulled off without a lot of people "in" on it, but it would require a lot of guesses and would be unlikely to be correct. I'm sure that whatever really happened makes a lot more sense than anything I could imagine, and NIST's version of things as well. If anyone's still interested in discussing the science of it, the biggest mystery for me at the moment is the glowing molten metal that is seen dripping from one of the towers. I think that the official explanation has been debunked.

I'm not caught up in this conversation but... A world line of an object is the path of that object through 4d spacetime. The world line is defined by its object. Different objects would each have their own world lines. You could though describe the world line of a molecule, or describe world lines for each of the molecule's atoms and they'd be very close to "the same" world line at macroscopic scale. Where two world lines intersect, you have two objects collocated in spacetime. A collision event might be described that way, where the collision event is essentially on both world lines... the same point could be said to be on both world lines, even though each world line is still associated with its own object. I suppose that some sets of objects can never occupy the same place and time, so their world lines would never touch.

I'm having trouble understanding how the WMAP diagram and a 2D diagram of what's observable fit together. Is the WMAP image a representation of the entire universe (of which we don't know the size, right?), or just the observable universe? What I think is that it is not meant to be either, but rather just a diagram of history, or the history of distance, where the bell-shaped curve is the distance between two completely arbitrary astronomical spatial coordinates??? Yes, the diagram is pretty empty, because it's a 2D image of a 4D representation of the universe. The galaxies and junk in the image are shown at one moment in time... but these don't exist only for a moment of time! Every object in the diagram could be "extruded" along the time dimension to show its history. Every bright object would have a "birth" along the time axis where presumably it formed from less luminous materials, and each would eventually have a "death" where it exploded or evolved into other things. So, everything that's in this diagram can be traced back through time to an earlier part of the diagram. None of the objects that you show outside the light cone should have come from an earlier part of the universe that was outside the light cone. That is, something that's 15 billion LY away and unobservable to us right now, was something else in the past, say 13 billion years ago when it was 13 billion LY away from us and thus visible to us at the moment.* Your "empty diagram" suggests that visible things are blinking in and out of existence, instead of existing for long periods of time and only being observed in single instants. Presumably, the objects on the diagram are placed "illustratively" roughly in the era that they existed as shown. I assume they'd want to be shown in formative parts of their lifetimes, rather than arbitrary times in their lifetime. But all the material that's shown in the diagram exists for the entire length of time in the diagram, in different forms as stars form and explode and reform into new stars etc. Smear the diagram horizontally from CMB to WMAP and vice versa, and even though it still only shows a handful of the hundreds of billions of observable galaxies, the diagram will become pretty full. * Note: I have a feeling this statement is wrong, due to my feeble understanding of inflation. A correction from someone who knows GR would be appreciated. Inflation must involve updates to simultaneity?? -- Due to inflation, an event may have been say only 12 B LY away, 13 B years ago local time, and be visible now 13 B LY away, right???

You keep using those words. I do not think they mean what you think they mean. Before you get too entrenched in scientific debate in the Speculations forum, you might want to brush up on a thread like http://www.scienceforums.net/topic/58293-frame-of-reference-as-subject-in-subjective-idealism/, where you will see that owl has already soundly defeated the "theory" of relativity, and his claims remain untouched by even the most seemingly convincing of logical arguments. I know 26 pages is a lot to read through, but as owl really dislikes repeating the same thing over and over and over, it would be courteous to get up to speed on the whole "What is IT that is time?" field of study so that we can skip any questions that have already been answered and go full speed into the ontological discussion of the quantum eraser experiment.