Where does ones relativity begin/end? [duplicate]

If there were a space ship moving close to the speed of light, that was large enough for a smaller ship inside of it to reach close to the speed of light and it opened its hanger doors and the smaller ship exited the larger ship at that speed, Theoretically, would it be crushed by its own mass at the door horizon, when it neared the door, after exiting the door, at all, or do we even know? (I'm not asking about relativity inside, because I know that neither ship is moving faster than the speed of light relativity speaking until the smaller ship exited the larger one, unless relativity changes as the ship approaches the door from the prospective of the person in the smaller ship). Which brings up what would it look like to the person in the larger ship from an angle where they could see out the hanger door, perspective of the small ship as it approached the door and to an outside observer (or camera) watching through the windows into the larger ship seeing the smaller ship (from that point of view moving faster than the speed of light) would it disappear, or would they just see it after?

marked as duplicate by Kyle Kanos, Jon Custer, glS, John Rennie special-relativity StackExchange.ready(function() { if (StackExchange.options.isMobile) return; $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() { var$hover = $(this).addClass('hover-bound'),$msg = $hover.siblings('.dupe-hammer-message');$hover.hover( function() { $hover.showInfoMessage('', { messageElement:$msg.clone().show(), transient: false, position: { my: 'bottom left', at: 'top center', offsetTop: -7 }, dismissable: false, relativeToBody: true }); }, function() { StackExchange.helpers.removeMessages(); } ); }); }); Sep 6 '18 at 16:24

• It doesn't work like that. Your question implies that there's an absolute reference frame that limits how fast you can go, but there isn't one. Also, to combine speeds properly you can't just add them together. That's approximately correct for low speeds, but it's hopelessly wrong at speeds near the speed of light. – PM 2Ring Sep 6 '18 at 6:12
• Eg, if the mother ship is going at 4c/5 relative to the outside observer, and the small ship is going at 3c/4 relative to the mother ship (in the same direction), then in the outside observer's frame the small ship isn't going faster than light at 31c/20, it's only going at 31c/32. – PM 2Ring Sep 6 '18 at 6:19
• would it be crushed by its own mass at the door horizon please read physics.stackexchange.com/q/3436/25301 and physics.stackexchange.com/q/133376/25301 – Kyle Kanos Sep 6 '18 at 10:18

From the larger ship's perspective, the smaller ship shoots off at the speed of light. Beyond that, nothing dramatic happens.

Being inside another ship doesn't actually mean anything. It's just a matter of reference frames. From the perspective of the larger ship, the smaller ship inside it is moving at close to the speed of light. Whether the smaller ship is inside or outside the larger ship isn't relevant, it is still moving at the same speed. Since you've given that the smaller ship is moving at close to the speed of light in the reference frame of the larger ship, then once it exits the hangar it's still moving at close to the speed of light in the reference frame of the larger ship. That means it shoots off, and nothing else happens.

• Looks like you've chosen the wrong reference frames. By definition, the small ship is moving relative to the large ship. – user191954 Sep 6 '18 at 6:46
• Question is a bit confusing, but OK, edited. – Allure Sep 6 '18 at 7:48
• Ok, that makes sense from the perspective of the larger ship, but how about from an outside bystanders point of view.. what happens when the smaller ship exits the large ship, wouldn't it be moving faster than light ... but that's impossible isn't it? – Sirgregory1st Sep 9 '18 at 1:47
• How about from an outside bystanders point of view.. what happens when the smaller ship exits the large ship? I thought that because of relativity the smaller ship would be moving at different speed relative to the different perspective. For example if the larger ship is moving at 2.99e8 m/s from an outside observer point of view and the smaller ship inside is moving at 2.99e8 m/s from the larger ships perspective. to an outside observer wouldn't the smaller ship exit the larger ship at around 5.98e8 m/s to an outside observer? – Sirgregory1st Sep 9 '18 at 2:12
• @Sirgregory1st no it wouldn't, addition of velocities doesn't work that way. See e.g. hyperphysics.phy-astr.gsu.edu/hbase/Relativ/einvel.html. Velocities cannot add to be faster than the speed of light. – Allure Sep 9 '18 at 3:10