Recent content by Jun Pan

Yes. When the spaceship rests on the earth, in the Earth coordinate (x,y,z,t), the simultaneity is defined without any doubt in the Earth coordinate system (x,y,z,t). So the moment the spaceship flies can be chosen as t=0 in (x,y,z,t), t'=0 in (x'.y',z',t'),and choose the spatial point x=0 in...

When the observer going away looks at an accelerometer to deduce that the spaceship is accelerating means this observer does not choose the spaceship as the rest frame, but instead chose other frame such as the frame the Earth rests as the rest frame. Yes, the green line is longer. However in...

During the period of acceleration, the observer in system 1 thinks the system 1 is inertial while the system 2 is not inertial system, and the observer in system 2 thinks system 2 is inertial while the system 1 is not inertial. This situation is symmetrical for two systems.

1, For Earth (x,y,z,t) chosen as 'rest' frame, spaceship (x',y',z',t') move away at speed v; for spaceship(x',y',z',t') chosen as 'rest' frame, Earth (x,y,z,t) moves away at speed -v. 2, When t=t'=0, let x=x'=0, or let two coordinate systems have the same start point. 3, According to the...

True, the turning point is the half way point observed from the Earth (x,y,z,t). But it seems to me that the turning point observed from the spaceship (x',y',z',t') can not be regarded as not the half way point. If according to the (x,y,z,t), the turning point observed from (x',y',z',t') is not...

I have read your insight. If to chose the spaceship as the rest inertial frame, from the view of the twin in the spaceship, the twin on the Earth is younger. When the two twins meet, neither one is younger.

I am sorry there is a mistake of my last post. It is supposed to me the twin going away will not be younger than the twin on the earth.

Yes, the definition of simultaneity is coordinate-dependent. There are two coordinate systems considered here or the Earth coordinate system (x,y,z,t) and the spaceship coordinate system (x',y',z',t'). Define when t=t'=0, x=x'=0. Spaceship is always at rest in the spaceship coordinate system...

If there is good definition of simultaneity, the Earth coordinate system and the spaceship coordinate system are symmetrical and the so the time dilation effects are symmetrical for these two systems.

The reciprocal time dilation and relativity of simultaneity can be derived from each other. I understand now. Thank you. If to consider the light travels in spaceship from A to B in the perpendicular direction to the spaceship move direction, this light beam observed from the Earth has the speed...

I have read your insight "A Geometrical View of Time Dilation and the Twin Paradox". I understand your meaning. Thank you. Indeed simultaneity not only links to time delay but also links to time units change. In this regard, simultaneity indeed plays a central role in time dilation. If I...

My understanding is time dilation is in the determination of how many ticks a clock in motion within time period of inertial frame 1 observed from another inertial frame 2 or how much time elapsed within one tick of the clock of inertial frame 1 observed from another inertial frame 2. In special...

Time dilation means time units dilation but does not specifically mean time points shift. The time units dilation between observer 1 in inertial frame 1 and observer 2 in inertial frame 2 are symmetrical for each other. There is not much relation between time units dilation and the relativity of...

I understand that no matter if there is return trip or not, time dilation exists in the whole period. In any scenario, observer 1 in the inertial frame 1 observes observer 2 in the inertial frame 2 moves at v, while observer 2 in the inertial frame 2 observes observer 1 in the inertial frame 1...

At the moment of explosion, there is big outward momentum on materials and gases from the explosion center away outwards. I think it is difficult to create the vacuum at the center. There should be outward momentum gradient and so pressure gradient from the center away. And how many forces is...