All observers agree on why the train makes it through the tunnel.

[md65536]

From a thread in the astronomy forum:

 

The video explain it very well :

I just want to disagree with the statement that "the reason why they agree that the train doesn't get smashed is different," which I've seen stated before in these forums.

 

The reason the train doesn't get smashed is the same in all frames: The front guillotine comes down before the front of the train reaches it, and the the back guillotine comes down after the back of the train passes by. Each of these two things describes an event that happens at a single respective location (the location of the respective guillotine), and all observers agree on those statements. The fact that the two events are simultaneous in the tunnel observer's frame is beside the point, and is NOT a necessary part of the reason that the train isn't smashed. It is merely circumstantial.

 

The only way that observers would disagree on what is happening, is if they describe it in a frame-dependent way (such as relying on the two causally unconnected events occurring "at the same time"). But describing the reason something happens is describing causality, which isn't frame-dependent. The cause of the train's survival is not frame-dependent.

 

 

That type of statement, that the reason is different depending on frame, fits with the interviewer's incredulity, and with other statements like "If you get a stupid answer you've probably done it right because the results of special relativity are so bizarre." It's only bizarre if you're holding on to the concepts of absolute time and length, and thinking along the lines of "measuring things differently means the reasons that things happen are different". I feel that such statements are detrimental to understanding relativity because they suggest that it is incomprehensible, and that incorrect outdated notions still "make sense" even if they're wrong, and so there is less incentive to let go of those wrong notions while learning.

 

The description of what happens is different, but the reason why it happens is the same.

 

Just 2 cents.

Edited April 23, 2014 by md65536

[SamBridge]

Right, because they are separated by physical difference in space the information about events take finite time to reach any given observer, the events that are separated by distance can be measured as happening at a different time in another frame even if they appear to happen at the same time in one frame since the distance between events and the time they take to achieve that certain relative distance is also relative.

If say, I'm holding one ball in both my hands, and I measure my throwing my arms and releasing them at the same time, a near-light observer approaching me would have to measure that the electrical impulses that went from my brain to both my right arm and left arm took more time in a longer distance to reach one arm but not the other, so really it's nothing that special, its a direct result of the relativistic all effects we already know at the same time.

Edited April 23, 2014 by SamBridge

[md65536]

Close enough I guess. Yes, I'm adding nothing new to the resolution of the train tunnel paradox. The resolution is straightforward special relativity. It's just that the description of it can be reasonable and straightforward in relativistic terms, or weird and confusing with classical ideas treated as what should be expected.

[DimaMazin]

I feel that such statements are detrimental to understanding relativity because they suggest that it is incomprehensible, and that incorrect outdated notions still "make sense" even if they're wrong, and so there is less incentive to let go of those wrong notions while learning.

 

Things of disagreement of observing exist. They create the question "Why?". It's useful for future discovery.