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There is nothing intuitive about special relativity. If you want to understand SR (or GR or QM), you must throw intuition out the window and strictly follow the

There is nothing intuitive about special relativity. If you want to understand SR (or GR or QM), you must throw intuition out the window and strictly follow the rules of the theory. The best explanation for why FTL breaks causality that I have seen is the tachyonic antitelephone: https://en.wikipedia.org/wiki/Tachyonic_antitelephone https://en.wikipedia.org/wiki/Tachyonic_antitelephone Drawing a bunch of spacetime diagrams might help as well.

sunaurus 4y ago
Thanks, that's what I was afraid of. I guess I've been trying to look for a shortcut, but in the end I'll have to dive much deeper and learn much more to really understand this topic. I've read the tachyonic antitelephone article several times over the years, but the problem is that (as far as I understand it), this thought experiment exactly boils down to "the numbers don't add up without breaking causality", without really explaining why that is in any intuitive way for me.
- hgsgm 4y ago
  Please define "causality", as precisely as you can. Presumably you'll need a "clock" of some kind, so please describe a clock in a way that it is independent of the speed of light and any particular frame of reference (unless you believe there is a preferred frame of reference. If so, which one is / which ones are?) Remember that the theory and experiment of special relativity state and show that the speed of light is always measured to be a constant, no matter who measures it and how they are moving with respect to anyone else.
dataflow 4y ago
Just because there's one unintuitive step that doesn't mean everything following that is incomprehensible without math though. The fact that the speed of light is constant might be unintuitive, but once you accept that, the fact (for example) that you can never reach it is intuitive. As is the fact that it would require infinite energy to do so. It's perfectly fair for someone to seek an intuitive explanation even with an unintuitive assumption. I have no idea whether there is one in this case, but it doesn't seem true that there's nothing intuitive about special relativity.

sunaurus 4y ago

Thanks, that's what I was afraid of. I guess I've been trying to look for a shortcut, but in the end I'll have to dive much deeper and learn much more to really understand this topic. I've read the tachyonic antitelephone article several times over the years, but the problem is that (as far as I understand it), this thought experiment exactly boils down to "the numbers don't add up without breaking causality", without really explaining why that is in any intuitive way for me.

hgsgm 4y ago
Please define "causality", as precisely as you can. Presumably you'll need a "clock" of some kind, so please describe a clock in a way that it is independent of the speed of light and any particular frame of reference (unless you believe there is a preferred frame of reference. If so, which one is / which ones are?) Remember that the theory and experiment of special relativity state and show that the speed of light is always measured to be a constant, no matter who measures it and how they are moving with respect to anyone else.

dataflow 4y ago

Just because there's one unintuitive step that doesn't mean everything following that is incomprehensible without math though. The fact that the speed of light is constant might be unintuitive, but once you accept that, the fact (for example) that you can never reach it is intuitive. As is the fact that it would require infinite energy to do so. It's perfectly fair for someone to seek an intuitive explanation even with an unintuitive assumption. I have no idea whether there is one in this case, but it doesn't seem true that there's nothing intuitive about special relativity.