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| | The discussion on this page is incorrect. Relativity does not say that nothing can travel faster than the speed of light, it says that objects with mass cannot travel at the speed of light. Massive objects can either travel below or above the speed of light. {{unsigned ip|108.162.237.183}} | | The discussion on this page is incorrect. Relativity does not say that nothing can travel faster than the speed of light, it says that objects with mass cannot travel at the speed of light. Massive objects can either travel below or above the speed of light. {{unsigned ip|108.162.237.183}} |
| − | :Not as I read the wiki page on this: {{w|Speed_of_light#Upper_limit_on_speeds|Upper limit on speeds}}. Maybe if you could have negative mass could you travel faster than c. But according to the page, nothing with zero mass or any finite (positive) mass can move faster than c. And yes if it has mass, then the speed will have to be sharply smaller than c. (But can get as close to c as you like by pouring in more energy).--[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 14:15, 30 September 2015 (UTC)
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| − | It is actually that you can't accelerate to the speed of light if you're already going faster you won't automatically have a immeasurable speed that is almost C you will keep going at that speed theoretically. [[Special:Contributions/108.162.246.72|108.162.246.72]] 07:38, 22 September 2016 (UTC)
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| − | Cueball mentions Galileo. Is it because he went against the then-consensus on scientific knowledge and was punished, and others are accusing Cueball (and other "thought police") of attempting to do the same thing? [[Special:Contributions/108.162.210.196|108.162.210.196]] 11:35, 12 November 2016 (UTC)
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| − | Could someone explain to me why a GPS wouldn’t work if relativity didn’t exist? {{unsigned ip|162.158.186.156}}
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| − | :[http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html This is a good read.] [[Special:Contributions/172.69.210.28|172.69.210.28]] 06:43, 13 September 2018 (UTC)
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| − | ::It is a good read. To summarize the main points of that article:
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| − | ::* GPS satellites contain {{w|atomic clock}}s to keep time, and they broadcast their current time. A GPS receiver measures the amount of ''time'' it took for the signals to arrive from the satellites' known positions, using ''{{w|trilateration}}'' to determine the receiver's position. (This is different from ''{{w|triangulation}}'', which determines position by measuring ''angles''.)
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| − | ::* GPS satellites orbit at a speed of 14,000 km/h relative to Earth's surface. One effect of this is {{w|Time dilation#Velocity time dilation|velocity time dilation}}: time passes ''slower'' for GPS satellites than it does near Earth's surface, drifting 7 microseconds ''behind'', every day.
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| − | ::* GPS satellites orbit at an altitude of 20,000 km, which is far enough away from Earth's mass that {{w|spacetime}} curvature is different there. One effect of this is {{w|Time dilation#Gravitational time dilation|gravitational time dilation}}: time passes ''faster'' for GPS satellites than it does near Earth's surface, drifting 45 microseconds ''ahead'', every day.
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| − | ::* Combining those, time passes faster for GPS satellites, by a net 38 ''microseconds'' (10<sup>-6</sup>) every day, relative to near Earth's surface.
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| − | ::* But GPS precision depends on ''nanosecond''-range accuracy (10<sup>-9</sup>), so 38,000 nanoseconds drift would cause GPS precision to accumulate an ''additional 10 km of error every day''. GPS would still ''function'' – the satellites would still transmit, and the receivers would still calculate a position – but that position could be out by miles and miles; so if the purpose of GPS is to provide a reasonably precise position, then by that standard, GPS wouldn't ''work''.
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| − | ::* {{w|Albert Einstein}}'s theories of {{w|special relativity}} and {{w|general relativity}} enable GPS to predict ''velocity time dilation'' and ''gravitational time dilation'' (respectively), and thereby compensate for the error so that GPS can ''work''!
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| − | ::[[User:Yfmcpxpj|Yfmcpxpj]] ([[User talk:Yfmcpxpj|talk]]) 21:58, 5 September 2020 (UTC)
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| − | :::I'm sorry, but to me, your summary seems to make it sound like relativity is a problem that we are correcting for, rather than enabling anything. If relativity didn't exist, we wouldn't need to correct for velocity and gravitational time dilation. Mind you, that's only what I get from your summary, haven't actually read the article.--[[Special:Contributions/172.68.94.150|172.68.94.150]] 22:35, 24 March 2023 (UTC)
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