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On August 22 2006 12:14 maoam wrote:
I don't really care enough basically.
On August 21 2006 19:33 Bill307 wrote:Show nested quote +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.
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On August 22 2006 11:50 Bill307 wrote:Show nested quote +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.
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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.
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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.
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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:
http://en.wikipedia.org/wiki/Dark_matter
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.
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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.
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Cayman Islands24199 Posts
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.
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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."
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On August 21 2006 19:36 Bill307 wrote:Show nested quote +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.
i cant agree with you more
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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
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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.
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On August 22 2006 01:31 Rekrul wrote:
Reading stuff like this makes me feel like an ant.
One time while looking up at all the stars I couldn't think of anything to justify my existance.
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Interesting topic. Lets just wait how this will affect accepted therories like the Big Bang and Big Crunch.
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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. 
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On August 22 2006 12:23 SuperJongMan wrote:Show nested quote +On August 21 2006 19:33 Bill307 wrote: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?
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On August 22 2006 01:31 Rekrul wrote:
Reading stuff like this makes me feel like an ant.
I'm waiting for someone to reply to this and say
"YOU ARE"
and laugh at the bannings.
<3 rekrul
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iNcontroL
USA29055 Posts
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On August 21 2006 19:23 lil.sis wrote:
dope. a lot of physicists will cry themselves to sleep tonight.
lol
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GPS and Relativity in Physics Today
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.
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I dunno, maybe some guys on TL.net know better than those of us who've done courses in GR, and well known mathematical physicists.
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United States24803 Posts
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.
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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.
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EPT
