Needs to be a change in temperature or a temperature gradient..not just being cold. I just seriously doubt it is due to impact because of how careful i've been. And if it is due to impact then it is some seriously weak glass. I can tell it is pretty damn thin as well (looking at the crack, and comparing that to my wife's old EVO 4G that has a crack through it). You can tell the thickness isn't the same as what they typically place on the front of smartphones.
I appreciate your input but three points I would like to make:
* Judging by the number of posts around the Internet on the various Nexus 4 problems, they are having some consistency issues. It is very likely that I maybe received glass that wasn't well formed, or perhaps was put under extra strain during the assembly process. There are at least 2 different assembly lines operating in China and Korea.
* I'm sorry but I'm really tired of other people telling me about their phone not having a crack, so therefore I must have done something to mine. The assumption that all things coming off of an assembly line are exactly the same is very naive. In another forum I've been told things like "I've dropped my Nexus 4 X number of times and it still looks flawless. I'm not calling you a liar, but you must have been a lot rougher on your phone than I have for that to happen." Well, I'm happy for you if that is the case. I wish I would have gotten your rock solid Nexus 4 device but Google gave me this one. Thankfully, Google acknowledges that this is a known issue and are replacing it.
* If there was any significant impact I would expect more of a web-like glass shatter. There are not signs of impact anywhere. So if it was an impact that caused it, then this is some seriously weak glass.
I stand by my original theory that it was a thermal thing. I was using my phone while taking a poo. When I'm using it, the area right above the Nexus lettering gets really warm (not so hot that I can't touch, but noticeably warmer than any other phone I've previously had...this thing is a beast hardware wise so that isn't surprising). I sat the phone against a tile floor that was no doubt a lot cooler than the Nexus 4 was. When I picked it up, that is when I noticed the crack. It could have happened before then and might have been due to some impact that I just didn't notice...idk... I find it very strange that I owned an iPhone 4 for 2.5 years and never had a problem with any cracks anywhere while the Nexus 4 developed a crack under the same care and usage pattern in less than a week.
Well, the fact is, most people reporting cracked back ACTUALLY DID something. Whether they remember it or not is another story.
I use Stability Test app and baked my phone to 45C and guess what, the back never crack. Also as I said I take the phone outdoors and back indoors, the back never crack. I also used it without any protection for a week before my pouch arrived from UK.
Regarding your IP4, did you use it with a bumper? TPU case? Naked?
The truth is, the glass back is quite solid.
I'm not defending N4 like some fanboys. Just stating from my personal experience.
@Richteralan - If you want to donate your Nexus 4 to science (and really drive home your point that it wasn't thermal), I have a little experiment for you. Use your Nexus 4 to the point of the back being warm-to-hot and then go outside and push it up against a nice cold metal pole (on a fence or something). See what happens.
Does that constitute normal usage? I'd love to do it but didn't you mention that it happened under normal usage? Who will do what you've described?
If you disregard normal usage, I can crack both front and back within 1 second, using a gasoline soaked string. But what point does it prove?