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My teacher told me that todays smartphones wouldn't work if the theory of relativity hadn't been discovered, but he didn't explained why.

Qmechanic
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uuu
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    This question already has an answer. See http://physics.stackexchange.com/q/1061/ – hdhondt Apr 26 '16 at 03:56
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    he mentioned those two points, gps and smartphones separately – uuu Apr 26 '16 at 03:59
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    smartphones have a GPS app built in. – hdhondt Apr 26 '16 at 04:04
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    of course they have, but i think he meant sth else – uuu Apr 26 '16 at 04:06
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    Ask him what he meant, and add it to your question. Of course, they would not work at all if Quantum Mechanics had not been discovered. And neither would computers, tablets, etc. – hdhondt Apr 26 '16 at 04:09
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    Of course cell phones will work without GPS! Spend time in a city with narrow roads and tall buildings (or in those buildings) you'll still have good cell performance even with NO GPS fix. While GPS certainly helps the network direct your data to your current cell, with no GPS, they'd just ues something else - for example another common method like triangulation. However, if there was GPS and then suddenly it stopped globally, there may be problems because the backup methods may not be reliable or handle the sudden increase in the demand for triangulations. – uhoh Apr 26 '16 at 05:20
  • yes, ask him what he meant; but I suppose he just said two things to sound more convincing, and actually meant only gps timing. – Ilja Apr 26 '16 at 05:37
  • [pedantic] Your teacher's statement is similar to "We would all be floating around if we didn't have a theory of gravity." [/pedantic] – James Apr 26 '16 at 14:54

2 Answers2

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Of course cellular phone systems could work without GPS.

In fact, cell phones DID work before they carried GPS chips!

Bottom Line (moved to the top): if there was never GPS or an understanding of General Relativity, the system would have been developed just fine without it.

edit: I'd like to add a few items:

  1. Teaching is hard! Credit should be given to anyone who is willing to stand up every day and try to explain science concepts. It's necessary to adapt the information to the level of the group and even accommodate the range within the group. Give it a try sometime!

  2. Teaching can also provoke thought and independent learning. If a teacher 'pushes the envelope' a bit and you catch them, especially by thinking and independent research, remember it wouldn't have happened if the teacher had't brought it up to begin with, and planted those seeds.

  3. This PCworld article might be good for further reading. Some of it is speculative (e.g. 'your cell phone could...'), so take with a grain of salt.

Spend time in a city now with narrow roads and tall buildings (or inside those buildings) and you'll still have good cell performance even with NO GPS fix. Turn it off, take out the battery, then go somewhere else far away, into a building where you can't receive GPS, then put the battery back in an try to make a call, and it will still work. It may take a little longer to "find itself", but there are other ways to do this - like triangulation.

(note - useful GPS signals come mostly from above and you need at least 3 or 4, while cellular connections can happen from any direction or path, through walls or windows. Since in most cases the cellular signal is orders of magnitude stronger than a GPS signal, this also makes it easier.)

However, the triangulation requires careful timing from multiple cell towers or installations, and they also may use GPS to set their clocks. GPSDO GPS disciplined oscillator is a great way to have a low cost, automatically maintained clock. If we didn't have GPS, then the towers would implement something else, since it's only local timing that's important (to their interaction with the phones), any group of thee towers can just ping each other once in a while.

If GPS suddenly stopped without time to prepare, there could be substantial problems in some cellular systems, and some might stop working completely. However, if there was never GPS, the system would work fine using alternate methods, just like it used to!

Cell towers are connected to the larger network via cables, microwaves, and mostly these days by optical fibers. These networks also heavily rely on a broad distribution GPSDO clocks.

That's important also if you want to browse the internet on your "smart phone" instead of your "cell phone."

If GPS never existed, an alternate would have been found. If it suddenly stopped working, I'm going to hope that there are some backup methods there too. Maybe follow that up in Engineering Stackexchange.

uhoh
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  • If GPS didn't work, you're right we would just develop something that did. But even without an understanding of GR, GPS would work just as well as it does today. See this answer for why the necessity of GR is a myth. –  May 03 '16 at 08:02
  • @ChrisWhite thanks for that! Maybe it's better to call it an overstatement rather than a myth. Each satellite is in a slightly different orbit, so even relative to each other they would still drift apart in time, albeit much more slowly than the difference between orbit and surface. After a while a new factor would be added to compensate. And of course relativitistic effect would have been 'discovered' early on and probably explained not long after, reguardless. – uhoh May 03 '16 at 08:29
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According to general relativity, Time is not absolute . But in most of the electronic devices which we use, Time is taken as absolute (For easy calculations) in clock speeds.And when these devices interacts with satellites which are away from earth the difference in time would be a problem in accuracy. Hence the general relativity is used to correct the time difference and more accuracy is obtained. Please note that time passes slower near massive substances according to general relativity. Hope the doubt is clear.

Avi
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