I did and I still found your explanation doesn't work. Your forward trip is entirely within the light cone, and your return trip does not intersect the original trip as you say.
To have it work out as travel into the past, you first need to exit the light cone, then re-enter it (specifically, re-enter it in the lower half-cone representing the past). So, you have to make both trips at FTL speeds.
For any point in space time, draw a cone with that point as origin (actually a hypercone, but you can visualize it as a 3-d cone if you strip out one spatial dimension). The axis of the cone is the time axis running through the origin. The upper half of the cone's surface and interior represents the future, and the lower half represent the past. The sides of the cone represent light speed; light that can be seen by a person at this point converges on that point following this surface from the past, and light leaving the origin travels along this surface in the direction of the future. The cone's exterior represent points in space that are neither past nor future (or *either* past or future, which one will depend on observer's frame of reference, but from a causation standpoint they are *neither* because events in this region cannot affect events at the origin).
The slope of the sides of the cone is 1/c (or alternatively, -1/c). If you travel faster than light, you travel along a line with a slope that is between -1/c and 1/c. If the slope you are traveling on is between 0 and 1/c to one observer, there must exist an alternate frame of reference where your slope is between -1/c and 0.
In order to go back in time, you first go outside of the light cone whose origin is your starting point in space time; this requires traveling faster than light. But you aren't yet in the past. If you then turn around and travel in the other direction faster than light, you can re-enter the light cone at a point that is in the past relative to the origin. In order for this to happen, there must exist a frame of reference in which both lines of travel have negative slopes, otherwise you will re-enter the light cone at a point that is in the future relative to the origin.
Paraphrasing, GP said FTL travel is a sufficient condition for traveling into the past. Strictly that's not true as I just explained what additional condition must be met. But there's nothing in special relativity that says that once we allow objects to move faster than light, that additional condition cannot be met.
There's no evidence that running both vehicles for 200000 miles will result in equal energy costs. And please don't cite the flawed study as "evidence".
Prius batteries are recyclable, and have a 150000 mile warranty (in Cailfornia).
The post only said "There's a case to be made", which is exactly correct: the case is (yet) to be made. You hit the nail on the head. The linked article (which is surely politically motivated) is making an argument that's analogous to the mythical Laffer curve.
It's a step toward the soixante-neuf drive used by the ship Hwang Ho in Philip Jose Farmer's (under the peudonym of Kilgore Trout) "Venus on the Half Shell". So named because it could achieve 69000 times the speed of light, obviously.
Good point... People forget that caller ID is a misnomer. It's really only caller location. If your spouse or child calls you from a phone number unknown to you (maybe from a service station after his or her car breaks down, or some other emergency), and you reject the call, you wouldn't know that it's him or her calling you.
Caller ID is a convenience, not a right. Such a service wasn't available until about twenty-something years ago. Were our rights being violated up until that time?
Um, the point is that people will bring their cellphones to these events and they will use them to take photos. The actual participants in the events have no control over the observers in this regard.
I cannot understand not reading my post before replying.
Next will have complaints from parents whose children's recitals are marred by clicking cell phones, newlyweds whose vows were interrupted by the same, etc., etc.
Slashdot Mirror
they can do something about this "The update "Java for Mac OS X 10.5 Update 4" can't be installed error message I get when I try to install the thing.
I did and I still found your explanation doesn't work. Your forward trip is entirely within the light cone, and your return trip does not intersect the original trip as you say.
To have it work out as travel into the past, you first need to exit the light cone, then re-enter it (specifically, re-enter it in the lower half-cone representing the past). So, you have to make both trips at FTL speeds.
As in, "I got a wrong number yesterday".
Then let's say you decide to travel back at some speed faster than light, like 0.5C or 0.1C.
Either of those choices would be slower than light.
For any point in space time, draw a cone with that point as origin (actually a hypercone, but you can visualize it as a 3-d cone if you strip out one spatial dimension). The axis of the cone is the time axis running through the origin. The upper half of the cone's surface and interior represents the future, and the lower half represent the past. The sides of the cone represent light speed; light that can be seen by a person at this point converges on that point following this surface from the past, and light leaving the origin travels along this surface in the direction of the future. The cone's exterior represent points in space that are neither past nor future (or *either* past or future, which one will depend on observer's frame of reference, but from a causation standpoint they are *neither* because events in this region cannot affect events at the origin).
The slope of the sides of the cone is 1/c (or alternatively, -1/c). If you travel faster than light, you travel along a line with a slope that is between -1/c and 1/c. If the slope you are traveling on is between 0 and 1/c to one observer, there must exist an alternate frame of reference where your slope is between -1/c and 0.
In order to go back in time, you first go outside of the light cone whose origin is your starting point in space time; this requires traveling faster than light. But you aren't yet in the past. If you then turn around and travel in the other direction faster than light, you can re-enter the light cone at a point that is in the past relative to the origin. In order for this to happen, there must exist a frame of reference in which both lines of travel have negative slopes, otherwise you will re-enter the light cone at a point that is in the future relative to the origin.
Paraphrasing, GP said FTL travel is a sufficient condition for traveling into the past. Strictly that's not true as I just explained what additional condition must be met. But there's nothing in special relativity that says that once we allow objects to move faster than light, that additional condition cannot be met.
This happened in National Lampoon's European Vacation, but the Griswold's weren't so lucky about their image not being used "in an unseemly manner".
You forgot the link.
Suspicions rise when he's the only student in the auditorium, yet attendance is registering full...
"It runs on air!"
Third time is the charm right?
Not if it's on Fox.
There's no evidence that running both vehicles for 200000 miles will result in equal energy costs. And please don't cite the flawed study as "evidence".
Prius batteries are recyclable, and have a 150000 mile warranty (in Cailfornia).
The post only said "There's a case to be made", which is exactly correct: the case is (yet) to be made. You hit the nail on the head. The linked article (which is surely politically motivated) is making an argument that's analogous to the mythical Laffer curve.
Don't laugh, it's been done. There was a sketch on SNL back in the seventies, where a cockatoo was dancing to "Macho Man".
...with the ILOVEYOU virus.
be behind the preference of some people for LPs over CDs?
What do you mean, an infant human body, a child human body, or an adult human body?
Sincerely,
Wolfram Research, Inc.
Throw back the little ones
and pan-fry the big ones
use tact, poise and reason
and gently squeeze them
It's a step toward the soixante-neuf drive used by the ship Hwang Ho in Philip Jose Farmer's (under the peudonym of Kilgore Trout) "Venus on the Half Shell". So named because it could achieve 69000 times the speed of light, obviously.
Good point... People forget that caller ID is a misnomer. It's really only caller location. If your spouse or child calls you from a phone number unknown to you (maybe from a service station after his or her car breaks down, or some other emergency), and you reject the call, you wouldn't know that it's him or her calling you.
Caller ID is a convenience, not a right. Such a service wasn't available until about twenty-something years ago. Were our rights being violated up until that time?
He might be logged in but posting anonymously, that means he can see the sig, which BTW is "So this is how Linux dies. With thunderous applause."
I can't get no power, Captain. Send down more whiskey!
Um, the point is that people will bring their cellphones to these events and they will use them to take photos. The actual participants in the events have no control over the observers in this regard.
I cannot understand not reading my post before replying.
Next will have complaints from parents whose children's recitals are marred by clicking cell phones, newlyweds whose vows were interrupted by the same, etc., etc.
Learn to use teh Google.