Background: in brief, dark matter is some kind of matter out in space that we cannot see. Even though we cannot see it, we know that it must exist because of its gravitational effects on other things.
For example, we have observed that stars (like our sun and solar system) orbiting the centre of a galaxy (like our own Milky Way galaxy) orbit a LOT faster than we'd expect. One possible explanation is that our theory of gravity is wrong, and doesn't work on large scales like the orbit of stars around the centre of a galaxy, or galaxies orbiting around the centre of a galaxy cluster. Another explanation is that there is a LOT of extra mass that we simply have not seen or detected yet. How much is "a LOT"? Well, one cluster of galaxies called the Coma Cluster has ~400 times as much mass as we can see. We refer to this extra mass as dark matter.
Dark Matter is likely a combination of many things, but we don't know what. Black holes are definitely one contributor, but there are probably others as well. For example, one exotic possibilitiy is that there is some new, almost totally undetectable form of matter that we have never seen before, and this invisible matter is responsible for much of the extra mass that we cannot see.
Explanation of the Evidence: look at the first picture in the article above. Click on the link that says "Press Image and Caption" right below it. This gives a good explanation of the picture and how it proves the existence of dark matter. Another explanation can be found on Wikipedia's entry on the Bullet Cluster.
I found this sentence (from the "Press Image and Caption" link) to be particularly interesting (emphasis mine):
Most of the matter in the clusters (blue) is clearly separate from the normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark.
So, in conclusion, we may not know what the dark matter is made of, but at least we have reaffirmed the correctness of our theory and understanding of gravity works .
On August 21 2006 19:21 {ToT}Strafe wrote: WOW THIS IS SO FUCKING AWESOME !! THIS IS SO COOL THAT I DONT KNOW WHAT IM GONNA DO NEXT. WOW.
It's a simple rule that you don't run around posting "I don't care" in topics that don't interest you. You've been here how long and yet you still can't do this one simple thing?
On August 21 2006 19:29 haduken wrote: can some one explain how this find will benefit anything practical -.-.
Nope. It's common for things to happen in science and math that have no practical application at the time they're discovered, yet become crucially important later on, e.g. complex numbers.
So I'm confident it will have practical benefits. We just can't explain them to you because we don't know what they will be.
G. H. Hardy, a very brilliant and well-known mathematician was quoted as saying:
"I have never done anything 'useful'. No discovery of mine has made, or is likely to make, directly or indirectly, for good or ill, the least difference to the amenity of the world."
However, since his time pure mathematics has found many practical applications in cryptography (elliptic curves, number theory etc.).
while the discovering of dark matter might not directly do much, such as bottling it and selling it at the grocery store, expanding our minds and learning for the sake of learning is why we are where we are today. For instance, spending half a trillion dollars on sending a man to mars is a complete waste of time and resources, but if we were to accomplish this i cant help but imagine the incidental benefits which would automatically unfold unto our society. We create advanced rockets which are useless except for short distance space travel (relatively speaking), and a guy stands around stomping his feet into red dirt. Yet our collective minds rejoice in the idea, kids seek interest in higher education, the sciences flourish, and some guy makes a car that runs on nothing. Spending our time educating ourselves in anything usually has some benefit here or there.
Strafe does it right. Writes a trolling post that took him 7 secs to conjure up and gets some 10 or so replies that actually try to explain it to him .
On August 21 2006 19:51 NewbSaibot wrote: while the discovering of dark matter might not directly do much, such as bottling it and selling it at the grocery store, expanding our minds and learning for the sake of learning is why we are where we are today. For instance, spending half a trillion dollars on sending a man to mars is a complete waste of time and resources, but if we were to accomplish this i cant help but imagine the incidental benefits which would automatically unfold unto our society. We create advanced rockets which are useless except for short distance space travel (relatively speaking), and a guy stands around stomping his feet into red dirt. Yet our collective minds rejoice in the idea, kids seek interest in higher education, the sciences flourish, and some guy makes a car that runs on nothing. Spending our time educating ourselves in anything usually has some benefit here or there.
Gravity is a theory thats tries to explain to happens in our reality. One day someone can come up with a better theory that explains why you cant jump off a cliff without a parachute but ALSO, what happens with that extra mass in the universe.
As far as all this "how will it be practical?" stuff, I could go into story telling mode and explain how sending men to the moon was pointless and did nothing, however the advancements in technology resulted in the very computers that we are all sitting in front of now...or how delving into completely theoretical and crazy studies resulted in the advancement of many medical procedures...
But instead I'm going to tell you you're being douchebags and direct you to a song that shows how stupid your attitude is.
On August 21 2006 19:21 {ToT}Strafe wrote: WOW THIS IS SO FUCKING AWESOME !! THIS IS SO COOL THAT I DONT KNOW WHAT IM GONNA DO NEXT. WOW.
It's a simple rule that you don't run around posting "I don't care" in topics that don't interest you. You've been here how long and yet you still can't do this one simple thing?
A common example of clueless people who make very many posts. That's why I find the "I have more posts" "more important than you" thing to be obsolete.
And like a few people have said, this "finding" (which is not really a proof of anything, only hypotheses) does not have any real impact on our lives on Earth. It only opens up new theoretical physics which is researched purely for the "fun" of it. The finding of dark matter merely shows that there are loops to be filled in our view of how the universe is kept together and has no practical application.
this is like Stephen Hawking making all these super dooper discoveries about things that no one ever thought about and then... OOPS we detected radiation from something that was 5+ billion years old... sorry steve... your theory just got shat on...
basically most of astronomy and the relevant sciences are based on philosophical principles. i.e. weak anthropic principle: The observed values of all physical and cosmological quantities are not equally probable but they take on values restricted by the requirement that there exist sites where carbon-based life can evolve and by the requirements that the Universe be old enough for it to have already done so."
which basically say that "we exist so something must have brought us to existence just the way we are now"...
so it's like knowing what y and x are but not having the equation... so we're basically putting any sorts of equations together and saying "this equation is correct because we get the right values of x and y (which we already know)"... when really there's so many probabilities and so much speculation that it's almost worthless to even try deriving the equation...
BUT.. like some people said in this thread.. it advances science, human thinking, etc., although I would argue strongly as to whether all these inventions (nuclear bombs, cloning, computers) are beneficial or not.
It pains me to think that there are people as ignorant as you, mazza.
The fact that physical models are made redundant by empirical observation is nothing original or surprising, we used to think that the Earth was the centre of the universe, and that it was flat.
Your criticism of "astronomy and the relevant sciences" is hilarious, and it is clear you do not understand the first thing about the substance or genesis of physical theories. I suppose Einstein threw "any sorts of equations together" when deriving general relativity, did he? Do you really have sufficient mathematical understanding to make such a statement? Do you know anything about physics beyond what is taught in schools?
Bernoulli's principle was pretty useless at one point, but now understanding of it allows us to fly. Maybe in the future all these "fun" discoveries will allow us to travel in space...
On August 21 2006 21:11 WhatisProtoss wrote: And like a few people have said, this "finding" (which is not really a proof of anything, only hypotheses) does not have any real impact on our lives on Earth. It only opens up new theoretical physics which is researched purely for the "fun" of it. The finding of dark matter merely shows that there are loops to be filled in our view of how the universe is kept together and has no practical application.
One hundred years ago humans worldwide lived a much more primitive lifestyle in comparison to today, your grandparents were raised by people brought up in victorian times for fucks sake... a hundred years might seem like a long time to you but believe me, it's not, and no one on this planet (in the present) knows enough or has the right to say dark matter has "no practical application"... you don't have a clue what you are talking about...
Edit: No offence man but what DO you know about dark matter? Where are you getting this "has no practical application" view from, do you actually have any knowledge on the subject whatsoever =/?
Well, based on the article linked in the original post what is claimed to be the "proof" of dark matter is a new observation (collision of galactic clusters followed by a "separation" of dark matter and hot gas) which discredits some of the competing theories based presumably on modified general relativity. No doubt this is a quasi- big deal to the astrophysics community, but the article is sensationalized. It's just more evidence of what everyone already thought without any new hint as to the composition of dark matter...
On August 21 2006 20:58 CaucasianAsian wrote: wait wtf gravity is not what really what we thought?
WTF I'm going to finally jump off of a cliff without a parachute now that I know gravity is different! WOOT!
read the article, the entire point of it is that this new observation discredits theories about gravity being different on huge scales and confirms the dark matter theory
On August 22 2006 05:35 HnR)hT wrote: Well, based on the article linked in the original post what is claimed to be the "proof" of dark matter is a new observation (collision of galactic clusters followed by a "separation" of dark matter and hot gas) which discredits some of the competing theories based presumably on modified general relativity. No doubt this is a quasi- big deal to the astrophysics community, but the article is sensationalized. It's just more evidence of what everyone already thought without any new hint as to the composition of dark matter...
it's a pretty big deal because this is the first time they found any direct evidence
up until this point they just had to assume dark matter was there because of its measurable effects, but it could also have been caused by gravity doing some funky things on a huge scale, which can now be ruled out
The only news in this finding is that it has made it easier for some physicists to grasp the concept of dark matter and black holes, and thereby increasing their motivation for researching further, and perhaps onto more relevant areas of physics. The idea of a form of matter that is only affected by the gravitational force, based on large scale astronomical observations, has been around for some time.
On August 22 2006 04:26 Reason wrote: One hundred years ago humans worldwide lived a much more primitive lifestyle in comparison to today, your grandparents were raised by people brought up in victorian times for fucks sake... a hundred years might seem like a long time to you but believe me, it's not, and no one on this planet (in the present) knows enough or has the right to say dark matter has "no practical application"... you don't have a clue what you are talking about...
Edit: No offence man but what DO you know about dark matter? Where are you getting this "has no practical application" view from, do you actually have any knowledge on the subject whatsoever =/?
I think this is very interesting...
Actually, I do have knowledge on this subject. Do YOU? Probably not. Sure, it's interesting, I didn't say it wasn't. Dark matter is just basically compacted mass which is super-dense enough to not emit light. Simple. The only problem was trying to verify their existence through the patterns and behavior of nearby light-emitting systems. And that was possible by the observation of "collisions" and trying to remap how those particular shapes were formed as light/dark matter systems passed through one another.
And how is this going to benefit us? We are going to... live on dark matter? No, our bodies can't handle that kind of pressure for even a split second. We are going to..... USE this dark matter? We won't be able to isolate this matter in small quantities even IF we were able to get close enough to any type of dark matter.
The thought process on dark matter has been going on for a while. We know it exists (theoretically) and we know what it does (theoretically).
Why is this different from what you say? Okay, so if the primitive people knew what a car was, knew that it existed and what purpose it served... then they would know that they could USE it. Don't compare cosmos to civilization, idiot. Civilization is the creation of technology with the specific purpose in which to better our lives. Studying dark matter has no such intent.
Stop making your bullshit entries. You just throw shit out trying to belie your apparent low IQ.
No I don't have knowledge on the subject, that's not important. I also never said you didn't find it interesting... do you have a problem with me saying that I find it interesting? =/ Why the hell are you being so rude ?? I did say no offence!? I was just trying to point something out...
The point I am making is that if we are just discovering/theorising something you're not in the position to pronounce that it has no practical application. That's beyond blatant and yet your managing to call me an idiot with a low IQ.
I don't think he meant to be offensive with the thing about 'your' grandparents, because EVERYONES grandparents were raised by people brought up in the victorian era
I think he was just making a point, that things can change drastically, and a 100 years from now this might have some very practical application (I don't know if that's realistic, but I think that was his point) that today we can't see or understand.
On August 22 2006 07:52 WhatisProtoss wrote: Tell me, what theory cosmos-based has been used for practical applications? Theory of relativity? Does it? Give me an example.
Well, since it's so easy to give examples for Newtonian gravitation, I'll supply one for general relativity: GPS. Without GR it would be hopelessly inaccurate.
Strafe, why don't you explore physics today, and test whether or not nuclear strong beats gravity: a tall building, a sidewalk, and a pair of legs to jump with are all the equipment you need.
No I don't have knowledge on the subject, that's not important.
So, you DON'T know about dark matter. Yet, you proceed to try and bash others: "Do YOU know about dark matter? No!"
Tell me, what theory cosmos-based has been used for practical applications? Theory of relativity? Does it? Give me an example.
Did you just imply that you had a dick? @_@ No WAY!
aww man lol FA got it right,
On August 22 2006 08:00 FrozenArbiter wrote: I don't think he meant to be offensive with the thing about 'your' grandparents, because EVERYONES grandparents were raised by people brought up in the victorian era
I think he was just making a point, that things can change drastically, and a 100 years from now this might have some very practical application (I don't know if that's realistic, but I think that was his point) that today we can't see or understand.
im not offending your grandparents LOL?????
Edit: No offence man but what DO you know about dark matter? [/quote]
No I don't have knowledge on the subject, that's not important.
On August 22 2006 07:52 WhatisProtoss wrote: So, you DON'T know about dark matter. Yet, you proceed to try and bash others: "Do YOU know about dark matter? No!"
Dude I was never trying to bash you, thus the "no offence" I know nothing of dark matter, all I was trying to communicate was that I don't think anyone knows enough to say "IT HAS NO PRACTICAL APPLICATIONS".
Annnnnnnnnd if there's anything more lame than your-mom jokes ( still get a chuckle from me occasionaly ) it's dick-less jokes. Guess what. I am a male. Guess what. I have a penis.. get over it
On August 22 2006 05:35 HnR)hT wrote: Well, based on the article linked in the original post what is claimed to be the "proof" of dark matter is a new observation (collision of galactic clusters followed by a "separation" of dark matter and hot gas) which discredits some of the competing theories based presumably on modified general relativity. No doubt this is a quasi- big deal to the astrophysics community, but the article is sensationalized. It's just more evidence of what everyone already thought without any new hint as to the composition of dark matter...
What he said. And all attention to cosmology/astronomy is welcome imo.
On August 22 2006 07:52 WhatisProtoss wrote: Tell me, what theory cosmos-based has been used for practical applications? Theory of relativity? Does it? Give me an example.
Well, since it's so easy to give examples for Newtonian gravitation, I'll supply one for general relativity: GPS. Without GR it would be hopelessly inaccurate.
Wrong (that's why I put Theory of relativity out already), GPS is very accurate without relativistic scales. This has already been proved... welcome to 21st century. Plus, the distance at which GPS transmitters are located makes the probable error very small.
----
On August 22 2006 08:18 Reason wrote:
Guess what. I am a male. Guess what. I have a penis.. get over it
Um, I don't need to state such things to affirm that I am a male. Don't you wink at me, you gay! >.<
When petroleum was discovered by modern society, people were using whale oil to light their lamps. Once oil came, people discovered that they could light their lamps much more cheaply by refining oil into kerosene.
One of the side products of this refination was gasoline. People had no idea what to do with it, thought it was useless, and threw it away or burned it.
This is pretty interesting. Thanks for posting the findings here.
Although, I'm curious--what if dark matter exists in other places, such as on the Earth itself? I mean, if we can't see it, how do we know it's there (or isn't there)? I'm also curious if dark matter can be passed through, or if it's still a solid, although it isn't visible.
if dark matter existed on earth then common physic knowledge implies that earth inself must be either dark matter or part of dark matter. which is impossible because u can see shit.
As far as i don't care about Reason (i just ignore him) , Whatisprotoss is completly ridiculously clueless idiot.You have no clue about so many things and you still for some reason like to post your idiotic posts. EDIT: I'm not talking about that GPS thing.
Basically, the frequency emitted by GPS satellites is about 0.00000005% slower than the frequency that we receive on earth. The satellites intentionally emit a frequency slightly slower than the one we want to receive here on Earth to compensate for time dilation effects.
General relativity doesn't appear anywhere else in that article.
I'm about 60% of the way reading through this article and I have to say: you should have given us a summary -_-;;. If everyone ignores it because it's too long and isn't straight-to-the-point, then I don't blame them.
Edit: Okay, there is only ONE relevant paragraph in the whole bloody article. Honestly this is the last time I am ever going to read something like that again. Next time, quote the relevant sections, or else I think it's fair for everyone to disregard it.
It is completely false that the design of the GPS system ignores relativity theory. Relativistic effects in the GPS system are vitally important. The total difference in the rate of atomic clocks on board a GPS satellite and the reference clock at the USNO amounts to some 38,600 nanoseconds per day. (This is mostly due to a combination of the Sagnac effect for a clock which is moving wrt the GPS receiver, and the relative gravitational time dilation between a stationary clock on the Earth's surface and a stationary clock 20,200 km above the surface, as mentioned in the above quoted paragraph from Ashby's paper; frequency shifts in clocks on the ground wrt UTC due to inhomogeneties in the shape of the Earth also play a role.) In contrast, in order to maintain the accuracies listed above, the GPS system must maintain a timekeeping synchrony within 10 nanoseconds variation per day, indefinitely! The major way in which the 38,600 nanosecond per day discrepancy due to relativistic effects is accounted for is by building into the GPS software used to keep the satellite clocks in synch with each other and to synchronize GPS time with UTC an effective downward frequency shift of 446.47 parts per trillion in the orbiting atomic clocks. In addition to this basic conversion factor, GPS receivers are programmed to take account for the fact that slight eccentricities in the satellite orbits result in tiny periodic changes in the frequency of the orbiting clocks.
The best part is that it doesn't even tell us how much accuracy we would lose if we did not take time dilation into account.
So in conclusion, unless you can explain otherwise, this article is useless.
On August 22 2006 11:48 maoam wrote: You're right it does get quite technical, but I'd rather you didn't take my word for it.
Then post the link AND quote the key parts of the text. That way, if someone doesn't want to take your word for it, then they can just go and read the whole article.
Edit: by the way, before today I had always believed that it was crucial for GPS to take general relativity into account. But honestly, right now I'm just not seeing the evidence to back it up.
Well, that's basically asking me to explain all the pertinent calculations to a lay audience. I'd rather concede the argument than take the time to do that for the sake of "winning" a thread on tl.net
then why did u argue when you can not explain your point properly? We might all be clueless on this subject but at least WhatisProtoss try to explain his understanding instead of others who just call him wrong but tell anything why he is wrong.
I am going to go out on a limb here and suggest that this 'direct empirical proof' of dark matter that the Harvard Scientists presented is not really proof. More like a slightly more certain analysis than the previous. The paper: http://chandra.harvard.edu/photo/2006/1e0657/media/paper.pdf
On August 21 2006 19:21 {ToT}Strafe wrote: WOW THIS IS SO FUCKING AWESOME !! THIS IS SO COOL THAT I DONT KNOW WHAT IM GONNA DO NEXT. WOW.
It's a simple rule that you don't run around posting "I don't care" in topics that don't interest you. You've been here how long and yet you still can't do this one simple thing?
Read and contemplate. In the end, one is far stupider than the other... but it doesn't change the fact it's both stupid.
As for those who don't care or find it useless due to irrelevance, scientific discoveries, no matter the relevance is something that people should just be happy with. The future honestly is limitless, and to think that our generation has it good is nonsense. In the grand scope of things, our individual lives etc mean jack shit. It is only humanity's progress as a whole that means shit. Humanity is still sadly incredibly primitive.
This is coming from a International Affairs major and not a science major btw. I too have no idea what any of this really means cept what was spelled out in layman's terms. Humanity is still a fetus in the grand scheme of things.
On August 22 2006 11:48 maoam wrote: You're right it does get quite technical, but I'd rather you didn't take my word for it.
Then post the link AND quote the key parts of the text. That way, if someone doesn't want to take your word for it, then they can just go and read the whole article.
Edit: by the way, before today I had always believed that it was crucial for GPS to take general relativity into account. But honestly, right now I'm just not seeing the evidence to back it up.
Relativity actually does play into it... but it's mostly false that accuracy is lost by ignoring relativity in GPS systems. Sure, like Maoam said, there are so called changes in the "gravitational frequency." And I'm guess that there are only like ~10 ns of change in the frequency at most.... but there's no way to know which way or how exactly this changes the GPS system.
Relativity plays a minor role in GPS. Even without consideration for relativity, the margin of error would be small, not huge as people say it is. You're right, Bill, there isn't enough evidence that GPS needs relativity. And based on calculations made by physicists, it is not needed.
---- But really, this is all besides the point. I just asked for an example of where a cosmic-based theory was crucial in our practical lives... >_> GPS is not one of them.
Interesting read, but for obvious reasons I feel largely indifferent to this discovery. It's like the space and shit articles you read in popular magazines and think "wow i didn't know that, that's awesome, how cool" and the minute you put the magazine away the information is stored in the "things of low interest, with no significance" area of your brain.
On August 22 2006 07:33 WhatisProtoss wrote: Dark matter is just basically compacted mass which is super-dense enough to not emit light. Simple.
Hmm, actually, dark matter doesn't emit light not because it's actually "super-dense". Observational cosmology isn't my field, but wikipedia is clear enough:
In fact, the article there actually rules out super-dense matter as a possibility for dark matter (this makes sense, because dark matter is very difficult to detect while black holes are simple to detect via gravitational lensing, etc.). It's clear from the limited info available about dark matter that it's really not so simple at all.
I don't think it is correct to speak of a proof in the context of physical theories. Experiments either falsify or confirm a theory, but you can't proof a theory in a mathematical sense.
This discovery is a strong argument -- and that's probably what is meant by "proof" -- for the Dark Matter theory, since this theory can easily explain the findings, and according to the NASA article, it falsifies the "alternative gravity" (don't know the name) theory. But this doesn't make it a proof.
proof is an abused word, things like legal proof or scientific proof are not the same as mathematical proof. but what can you do. :/
but yeah sometimes a less rigorous "proof" is used to describe something, then the reader might not understand "proof" is not actually hard 100% proof.
Im not sure where this argument has landed, but when they say proof of dark matter, they mean quite literally proof. Maybe the following more simplified exerpt will help you understand-
NASA says it now has the first direct evidence for the existence of dark matter, thanks to observations of a huge, intergalactic collision.
Researchers using the Chandra-X telescope have been watching two galactic clusters collide, an event they say is the most energetic in the universe, ever, apart from the Big Bang.
They also used Hubble, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes to track the location of the mass in each cluster using gravitational lensing. This is the phenomenon whereby a sufficiently large mass can actually bend the path of light, so that you can see something that would otherwise be obscured by a massive galaxy, for instance.
As the two galaxy clusters smash into one another, the huge clouds of hot, gaseous normal matter encounter drag, similar to air resistance. Because of this, normal matter is slowed down by the impact of one cluster on another. Dark matter, on the other hand, continues unimpeded since it doesn't interact with normal matter, except through gravity.
This separation of the two types of matter shows up in the data, NASA says, and this provides the evidence that the dark matter is really there.
Most of the matter in the universe is thought to be so-called dark matter. It gets its name because it is effectively invisible, and until now its existence could only be inferred from its gravitational effects.
The term was invented to account for the fact that despite not having enough mass to hold themselves together under their own gravity, galaxies still spectacularly failed to tear themselves apart. Astronomers reasoned that something invisible, but massive, must be holding things together. Hence, dark matter.
However, not all scientists agree (and when do they ever?). Some alternative theories have been put forward, but NASA says only dark matter can explain the observations here.
Doug Clowe of the University of Arizona, and leader of the study, says the work has "closed the loophole" on gravity.
"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," he said "These results are direct proof that dark matter exists."
On August 21 2006 19:29 haduken wrote: can some one explain how this find will benefit anything practical -.-.
Nope. It's common for things to happen in science and math that have no practical application at the time they're discovered, yet become crucially important later on, e.g. complex numbers.
So I'm confident it will have practical benefits. We just can't explain them to you because we don't know what they will be.
On August 22 2006 07:33 WhatisProtoss wrote: then they would know that they could USE it. D Stop making your bullshit entries. You just throw shit out trying to belie your apparent low IQ.
of course for our current technology, its useless. But with thoughs like yours, it seems that humanity would have never evolved this much. Think of Galileo, Why the world would fucking care if it was round or square the planet.... Now we know you can go to the sea without falling to an abyss...
yes maybe this kind of knowledge is useless atm, but when we're able to travel through space (if we are ever able ) then this kind of knowledge might be put to some use
yea, i mean now that i know dark matter exists, im actually kinda glad my teleporter experiments failed, otherwise i might have teleported myself right into such dark matter and probably died or something, all the while thinking it was just empty space.
I've done a fair amount of general relativity, and this is how I understand the GPS thing: I know FOR SURE that a clock in orbit around the earth will not agree with a clock at the surface due to the different gravitational fields (general relativity) and different speed (special relativity). I am positive this affects the GPS satelites, but I cannot say by how much... I am also sure this is the effect in the quote Bill posted.
I do not know exactly how the GPS works, but I'm quite positive it involves sending light speed signals and then making time measurements to measure postion. So i ASSUME that if the satelites are a time t wrong, then the you will get an error in position of the order t*c. Using the figure in Bills quote 38.6*10^-6 (In the US, 38,600 means 38 thousand 6 hundred?) seconds per day, that would give around 38.6*10^-6 * 3*10^9 = 115.8 10^3 meters. That is: after just one day ignoring general relativity, you would get an error of about 100km.
But again, I'm not sure how a GPS works, and I may have missinterpreted the figure in Bills quote so this calculation may be wrong.
On August 22 2006 20:40 pH)ggbOy wrote: Interesting topic. Lets just wait how this will affect accepted therories like the Big Bang and Big Crunch.
Yes intereseting, but maybe not as revolutionising at they want it to seem. Almost everyone have already accepted the dark matter model, and this is just one in a row of observations of dark matter, if maybe the most direct. There is however a bit of work left to do regarding the future of the universe.
On August 21 2006 19:21 {ToT}Strafe wrote: WOW THIS IS SO FUCKING AWESOME !! THIS IS SO COOL THAT I DONT KNOW WHAT IM GONNA DO NEXT. WOW.
It's a simple rule that you don't run around posting "I don't care" in topics that don't interest you. You've been here how long and yet you still can't do this one simple thing?
Read and contemplate. In the end, one is far stupider than the other... but it doesn't change the fact it's both stupid.
Yes, how stupid of me to give up a fruitless argument instead of attempting to teach a lay audience GR, and then discuss the calculations involved in estimating the error introduced by relativistic effects on GPS.
I think that must be a new low, being called stupid by someone who majored in International Affairs. What next? MacDonalds employees pointing out holes in my proofs?
For those interested the article says relativity IS relevant for the GPS. According to it navigational errors amount to 11 km after one day without correction.
On August 22 2006 12:27 WhatisProtoss wrote: Relativity actually does play into it... but it's mostly false that accuracy is lost by ignoring relativity in GPS systems. Sure, like Maoam said, there are so called changes in the "gravitational frequency." And I'm guess that there are only like ~10 ns of change in the frequency at most.... but there's no way to know which way or how exactly this changes the GPS system.
Relativity plays a minor role in GPS. Even without consideration for relativity, the margin of error would be small, not huge as people say it is. You're right, Bill, there isn't enough evidence that GPS needs relativity. And based on calculations made by physicists, it is not needed.
---- But really, this is all besides the point. I just asked for an example of where a cosmic-based theory was crucial in our practical lives... >_> GPS is not one of them.
On August 23 2006 04:25 Cascade wrote: I've done a fair amount of general relativity, and this is how I understand the GPS thing: I know FOR SURE that a clock in orbit around the earth will not agree with a clock at the surface due to the different gravitational fields (general relativity) and different speed (special relativity). I am positive this affects the GPS satelites, but I cannot say by how much... I am also sure this is the effect in the quote Bill posted.
I do not know exactly how the GPS works, but I'm quite positive it involves sending light speed signals and then making time measurements to measure postion. So i ASSUME that if the satelites are a time t wrong, then the you will get an error in position of the order t*c. Using the figure in Bills quote 38.6*10^-6 (In the US, 38,600 means 38 thousand 6 hundred?) seconds per day, that would give around 38.6*10^-6 * 3*10^9 = 115.8 10^3 meters. That is: after just one day ignoring general relativity, you would get an error of about 100km.
But again, I'm not sure how a GPS works, and I may have missinterpreted the figure in Bills quote so this calculation may be wrong.
I don't have the numbers offhand but I do know that the effects of relativity are significant. Even if you disregard general relativity, the time dilation of the high-speed satellite will offset the clock. Over time, the problem continues and it gets more and more offset from Earth time. In addition, the offset in 1 day is substantial enough that after the order of magnitude of weeks or months, the accuracy of the theoretical locus of points generated by a gps device is pathetic and useless.
pH)ggbOy wrote: Interesting topic. Lets just wait how this will affect accepted therories like the Big Bang and Big Crunch.
Oscillating universe was pretty much ruled out by red-shift/blue-shift analysis of an outlying star a few years ago fyi.
On August 23 2006 08:53 maoam wrote: Yes, how stupid of me to give up a fruitless argument instead of attempting to teach a lay audience GR, and then discuss the calculations involved in estimating the error introduced by relativistic effects on GPS.
I think that must be a new low, being called stupid by someone who majored in International Affairs. What next? MacDonalds employees pointing out holes in my proofs?
I think the problem has been that from the beginning you claimed that you are very knowledgable then haven't really backed that up. You dropped some fancy terms to sound like you know what you are talking about, but stopped the moment you needed to show a deep understanding of the topic. Then you were a little overly rude when someone got annoyed about that (I admit you weren't the only one who got rude, but you didn't have to bite). You might be the world's foremost expert on this topic for all I know, but your statement about McDonald's employees implies a greater level of absurdity than has been witnessed in this thread.
On August 23 2006 15:30 micronesia wrote: I think the problem has been that from the beginning you claimed that you are very knowledgable then haven't really backed that up. You dropped some fancy terms to sound like you know what you are talking about, but stopped the moment you needed to show a deep understanding of the topic.
I don't claim to be an expert on physics (I have a degree in mathematics, though), or even on GR. I have done a graduate course on it, and I've read about this subject before (to be precise, about how the GPS system uses relativity). That is why I referenced the article on John Baez's site. I don't recall using any fancy terms, but if I did, I should certainly have used simple ones instead; however, as I have said several times in this thread, I don't see why I should be expected to reproduce the figures or calculations myself, when it's unlikely that the people I will be presenting them to have sufficient knowledge of physics.
Perhaps I should've taken the time to explain, in detail, exactly why GPS require GR, and exhibit a deep knowledge of the subject in the process. But I thought that people might take the word of a mathematical physicist (well, a guy with a PhD in mathematics who has published papers on GR) over mine, how can I explain it better?
GPS does adjust for gr, but i think the compound errors are grossly overstated since they can be easily corrected right? If every x seconds the satellite asked for the proper time from a land base system, the maximum error would then be limited to the change over the x seconds rather than a day
But that was a really cool article maoam, i'm much more impressed with the other adjustments they make in the gps systems.
On August 23 2006 18:16 testpat wrote: GPS does adjust for gr, but i think the compound errors are grossly overstated since they can be easily corrected right? If every x seconds the satellite asked for the proper time from a land base system, the maximum error would then be limited to the change over the x seconds rather than a day .
Yes, that is accounting for special relativity. The point is that there is a need to acknowledge the effects of relativity, whether or not he reason behind these effects is even understood.
On August 23 2006 04:25 Cascade wrote: I do not know exactly how the GPS works, but I'm quite positive it involves sending light speed signals and then making time measurements to measure postion. So i ASSUME that if the satelites are a time t wrong, then the you will get an error in position of the order t*c. Using the figure in Bills quote 38.6*10^-6 (In the US, 38,600 means 38 thousand 6 hundred?) seconds per day, that would give around 38.6*10^-6 * 3*10^9 = 115.8 10^3 meters. That is: after just one day ignoring general relativity, you would get an error of about 100km.
Ahhh. This is the kind of quantitative example I was waiting for . Even though your figure my disagree with that other one posted (11 km), I am starting to understand why the tiny difference in frequency can cause a monumental error. I didn't realize the frequency played such an important role. I'm also in awe of the accuracy of these instruments.
EPT
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![[image loading]](http://web.mit.edu/jsslee/Public/relativity.jpg)
