Help Low battery -- Phone turns off at 15%

That's how it's often phrased, and since energy and mass are partially interchangeable there's some truth in looking at it that way (I tend to define mass as "how much energy something has when it's at rest"). But the people who use relativity all the time generally use the word "mass" to mean something that doesn't change, to the extent that I only remembered there was another way of expressing it part way through my post.

Words are tricky - they mean different things to different people. Safest to stick to equations

Yeah, equations are concrete. You can't argue with them if the maths is sound.

Different topic; I don't know if this is your field but do you know anything about dimensions above the 4th? I can appreciate how time is the 4th dimension but I watched this video called Imagining the 10th Dimension and I couldn't really visualise the 5th-10th.

edit: re: the previous topic. So is it also untrue, as I was once told, that the reason objects can't travel at the speed of light is because they gain so much mass as their velocity approaches c?

It's certainly the case that a particle cannot be accelerated to the speed of light because the energy would have to be infinite at that speed. So when the kinetic energy becomes large compared to the rest mass, increasing the kinetic energy of the object further has increasingly little effect on the velocity. Whether you like to think of this as mass increasing as it gains energy, making it harder to increase the velocity, or use "mass" to mean an invariant property of the object and say instead that that's just how the kinematics (energy-velocity relation) work, is arguably a matter of taste as long as it's clear to your audience. Professionals tend to take the second approach, but since we know that mass can be converted into energy and vice-versa I'd say that the first is defensible if it helps you understand it.

As for extra dimensions, nobody can visualise them . We can write algebra for multi-dimensional spaces, but we can't picture in our heads any more than 3 perpendicular directions (I expect that the ability to do so would have little survival value!). If these things exist, they would be "extra directions" perpendicular to all 3 dimensions of what we perceive as space, and also perpendicular to each other (technically "orthogonal" is the actual word used). String theorists usually talk about these dimensions being very small (and I do mean very) and that being the reason why they are imperceptible to us. Whether they do exist is speculative - as an experimentalist I'll reserve judgement until there is some evidence, or at least a prediction we can test (well there was one testable prediction, that stuff about black holes at the LHC, and we didn't see any. But that was a much larger scale of extra dimension than the string theorists talk about).

I noticed the 'If'. I guess this stuff is not as concrete as I thought. For some reason I'm not fond of String Theory and it's proponents. Those guys seem heavy on marketing and light on substance.

Since you mentioned the LHC, I have another burning question. Do you have a better explanation for what the Higgs Boson is than that popular analogy about it being like Maggie Thatcher walking in a room full of politicians who are drawn to her as she moves through them?

And separately, if I travelled to the nearest star (4.5 light years away) and back at the speed of light, 9 years will have elapsed for me but how much time will have elapsed for the family I leave on Earth?

Nothing is definite in science, e.g. Newton's laws survived for a couple of centuries before we started finding things that didn't fit and discovered that they weren't the whole story. Extra dimensions currently come into the "no evidence as yet" category.

That analogy was very nicely crafted (not by me!) to appeal the the (tory) politician who was offering a bottle of champagne as a prize . I suppose could offer a different analogy (filling the universe with treacle, perhaps?). But the basic idea is that there is some quantum field whose average value in "empty" space is non-zero, and which interacts with other particles. Those other particles gain energy as a result of this interaction, and hence mass (E = mc^2 means that if a particle at rest has an energy E, that is equivalent to a mass m = E/c^2). The Higgs mechanism, or something like it, is necessary because just adding mass terms to the field theory destroys an important mathematical property which makes the theories actually usable. Doing it this way, via interactions with this extra field, preserves that property. Whether that is what actually happens in nature we don't yet know - if not, there must be some other process that produces the same effect, and that should also be accessible to the LHC. Arguably it will be more interesting if it turns out not to be the Higgs (it would spur more new thinking and some re-evaluation), but it's too early to say yet.

As for interstellar travel, it depends on how close to the speed of light you travel how much times has elapsed. But it's actually the other way round: if you travelled at 0.9*the speed of light, and we overlook the time taken to accelerate/decelerate, then 10 years would have elapsed on Earth but only 4.4 years for you. If you travelled at 0.95*c it would be 9.4 years on Earth but 3 years for you, and at 0.99c it becomes 9.1 years vs 1.3 years to you. To the observer on Earth it appears that you travel 4.5 light years each way but your clock is running slow. To you it appears your clock is normal but the distance is reduced (Lorentz contraction).

And as evidence that this is a real effect, we're both being hit by a couple of cosmic rays each second (easy to see them with the right apparatus). These particles are muons, produced in the upper atmosphere. But muons have a lifetime of 2.2 microseconds, so should only be able to travel about 700m before decaying (at speed close to c, but without time dilation). They only reach the ground because they are travelling fast enough that time (as we see it) is running slow for them.

And if you aren't a fan of string theory, you might like the punchline to this one: xkcd: Unscientific

To briefly return to the topic, I tried to run mine down the other week and failed - it got to 8% and was still going when I had to put it on charge. Maybe this is because of one time I did actually run it flat? But I'm so used to it shutting down at around 15% that this doesn't help me, 'cos once it reaches 20% I still feel like I'm minutes from shutdown and daren't trust it...

Hadron said:

As for interstellar travel, it depends on how close to the speed of light you travel how much times has elapsed. But it's actually the other way round: if you travelled at 0.9*the speed of light, and we overlook the time taken to accelerate/decelerate, then 10 years would have elapsed on Earth but only 4.4 years for you. If you travelled at 0.95*c it would be 9.4 years on Earth but 3 years for you, and at 0.99c it becomes 9.1 years vs 1.3 years to you. To the observer on Earth it appears that you travel 4.5 light years each way but your clock is running slow. To you it appears your clock is normal but the distance is reduced (Lorentz contraction).

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I had to read this a couple of times to get my head around it. So, interstellar travel isn't too bad with the Lorentz contraction shortening the distance, is it? This reminds of a blog I read by this guy who started 2 atomic clocks measuring time to microseconds(I think) and took one with him for a weekend at a mountain retreat with his kids. When they returned, the clock they left had gained a few micro(?) seconds. I know it's to do with the distance above ground, but how exactly does that all work ?

Also, is the maths for calculating time for interstellar travel (at relativistic speeds) very complicated or is there a simple equation?

Bit late to this thread guys, but I've just noticed it and thought I would comment anyway.

This problem with the battery turning off at, or > 15%. I've had it several times now, and yes there are several complicated and clever ways of fixing it, with long guides posted earlier as many of you have pointed out.

See for me, I wait until the phone auto-shuts down, and then plug in the charger. Leave the phone till it is fully charged (shut down) and then see if things have changed. Every time I've tried this it has solved it for me. Last few nights for example, flashed lots of different roms and the phone started shutting off at 18%. Did my trick, and now it just auto shut down at 1% this evening.

For calculating time dilation due to velocity it's very simple. Time slows down by a factor of gamma, i.e. 1/sqrt(1-v^2/c^2). So for v = 0.9c, gamma = 2.29, and hence time appears to be running slower by that factor.

But for interstellar travel the distances are still huge, especially since it's not easy to accelerate a significant mass to that the sort of velocity that would make a big difference (and decelerate it at the other end).

Time dilation due to altitude is General Relativity (i.e. a gravitational effect), which is much more mathematically involved. But it's a measurable enough effect that the GPS system, which relies on very precise timing, has to take it into account (sneakily bringing it vaguely back to android phones ).

Got physics fatigue yet? . Never leave me alone with a physicist. My curiosity killed Schrodinger's cat.

I better let the thread return to it's intended topic before I get banned.

williamj1 said:

See for me, I wait until the phone auto-shuts down, and then plug in the charger. Leave the phone till it is fully charged (shut down) and then see if things have changed. Every time I've tried this it has solved it for me. Last few nights for example, flashed lots of different roms and the phone started shutting off at 18%. Did my trick, and now it just auto shut down at 1% this evening.

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Good to see this trick is working for others. I'm still surprised it's so easy compared to the other calibration methods.

I...can't...resist. Last 2 questions. I promise. This was bugging me so much that I couldn't concentrate on the footy earlier on.

How much time elapses for a photon travelling to us from the nearest star? I'm sure it's not 4.4 years, however, gamma will end up being 1/sqrt(0) which doesn't work and as v approaches c, gamma becomes extremely large indicating that we approach instantaneous travel time. What gives?

And separately, one of the laws of thermodynamics is that energy can neither be created nor destroyed etc. etc. So how does that reconcile with there being no energy and then a universe full of energy respectively before and after the Big Bang?

Photons are tricky. The gamma factor relates time as I observe it to time in the moving spaceship's rest frame (i.e. as observed by the person on the ship), so the time I think has elapsed is gamma times what the astronaut thinks. But you can't apply the same logic to a photon, because it doesn't have a rest frame - the photon is always travelling at the same speed in any coordinate frame.

But there is a way of looking at it: the "interval" ds between 2 points in space-time is given by ds^2 = c^2dt^2 - dr^2, where "dt" = time difference between 2 points, while "dr" = spatial separation between them. The beauty of this is that it's "Lorentz invariant", i.e. you get the same answer irrespective of how fast you are moving or which observer you ask. So if a spaceship travels between 2 points at a constant speed, the interval between these points (the position and time when they set off and the position and time when they arrived) just equals cdt as measured by the astronaut - because in the astronaut's rest frame they are not moving (the planets are moving relative to them!) so dr = 0.

The way this helps becomes clear if we apply this to a photon: in a time dt the photon travels a distance dr = cdt, so the interval between 2 points in space-time connected by the emission and absorption of a photon is ds^2 = 0. So if we ignore the fact that the photon hasn't got a rest frame and treat this as the time elapsed in the photon's frame, we'd conclude that no time elapses for the photon (which is also consistent with gamma = 1/0, as that would imply time travels infinitely slowly for the photon, but I don't like being so casual with divide by zero or infinity, which is why I introduced the interval instead!).

As for cosmology, I remember an argument that gravitational potential energy (negative) balances the mass (positive) giving a universe with very little net energy. Whether that still works if the expansion of the universe is accelerating I'm not sure.

Hadron said:

The way this helps becomes clear if we apply this to a photon: in a time dt the photon travels a distance dr = cdt, so the interval between 2 points in space-time connected by the emission and absorption of a photon is ds^2 = 0. So if we ignore the fact that the photon hasn't got a rest frame and treat this as the time elapsed in the photon's frame, we'd conclude that no time elapses for the photon

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Fascinating!

Let me try and get this thread back on track. I reflashed the ROM the other day and when I let the phone run down it switched off at 13%. I started to recharge the phone with it switched on, waiting to 15% and then unplugged the charger. Waited until 13% but it didn't switch off. I waited to 11% and then plugged the charger in and charged the phone. Obviously, letting it power down must have reset the battery calibration.

What do you mean letting it power down must have reset it? I think the calibration was lost when you reflashed the rom.

I am just assuming that is what happened because I didn't plug the charger in as it was powering down. I let it power down completely before recharging it to 15% and then wait until it powered down, but it didn't. It just kept getting lower and lower. I hadn't calibrated it.

Interesting. Is this the only time it's cut out early for you?

It is the only time I have let it run down since I reflashed the ROM

So the battery calibration tut I posted didn't work? which kernel are you using?

I just realized I already posted earlier in the thread, the method I posted definitely works for me, I do it every couple of months.

ps, v. interesting thread for all the offtopic posts lol nice one

sure, i'll check back and see how u go

u can find out if your kernel is compatible with that app, download it and see if u get values in the boxes on the general tab, if there are numbers there then you should be good to use it. (assuming u haven't tried that particular one)

edit: this app https://market.android.com/details?id=net.jonrichards.batterycalibrator.ui&hl=en

edit2: following the method in the tut i posted takes ages, and u have to be watching the phone a lot for a while, in fact it's a real pain in the ass... but it's the only thing that actually works for me.

edit3: I think this could MAYBE work if you don't want the hassle: let the battery run down until the phone switches off, remove the battery for a bit. Put the battery back in and either 1- charge it to full while it's off 2- charge it to full, on airplane mode, switching any alarm/reminder apps off or anything that may draw power without direct user interaction, and basically don't touch the phone once it's past the 70% mark.

the way the battery charge works/is designed (afaik): once a learn flag is activated (which you can do with the app if your kernel is compatible, but arguably other things can trigger it, like letting the phone completely run out of battery, who knows) the more charged the battery gets the less voltage it draws. The phone thinks it's completely charged once the voltage it's drawing drops below a certain level. The problems happen when, for example, the phone is close to that threshold voltage that indicates it's charged and an app draws power which makes it reach that threshold. The phone will then stamp that level as the 100% level, even tho it's not, and deactivate the learn flag.

this is just how i understood it when i looked into it, hope it sheds some light on how the calibration app works

It might be that the shutting down reset your calibration a bit anyway. Did it shut down at 15%, or did you just decide that was far enough and recharge it?

I'd got so used to the idea that mine shut down at around 15% that I always plugged it in as soon as I could below 20. Then the other week I had a similar experience to madhatter - I tried really hard to run it down and see how low it went, and it counted down all the way to zero before shutting off, and like him I'd made no deliberate attempt at calibration.