A lot more people get PhDs in physics than can ever be scientists working at labs like CERN. A physics prof can typically have 3 or 4 PhD candidates working with him/her. Sometimes more. One guy at the school I graduated from had his own baseball team of PhD candidates. (That's nine people, for those who don't know from baseball.) That means on average a prof will graduate a PhD student every year or two over his/her academic life, maybe for a total in the range of 20 to 30. But only one is needed to replace that prof. Even in times when the field is expanding you won't see a large fraction of the PhD students getting academic positions.
That being said, it is rare for a PhD in physics to be unemployed. Not impossible, of course, just rare. It's just that they wind up in industry. In many cases, they wind up doing interesting work, but not particularly oriented towards research of academic journals or anything like that.
So look at it this way. Would you be doing this stuff in you spare time if you were employed doing something more "workaday?" So if you were employed as a nuclear safety analyst by a nuclear power utility (for example, I wonder who that could be) would you be reading about particle physics in your off time? If so, maybe you still want your degree to be in particle physics. Do it if you love it and have an aptitude for it.