The discussion revolves around the relationship between time measured from the Earth and time measured from the Sun, particularly in the context of the approximate 8-minute light travel time between the two. Participants explore whether this time difference is influenced by Lorentz transformations or is simply a consequence of the speed of light. The conversation touches on concepts of simultaneity, time dilation, and the implications of different reference frames.
Participants express differing views on the interpretation of time measurements from the Sun and Earth, with no consensus reached on whether Lorentz transformations play a significant role in the 8-minute time difference. The discussion remains unresolved regarding the implications of simultaneity and the effects of different reference frames.
Participants note that the discussion involves assumptions about the rest frame of the solar system and the effects of gravitational time dilation, which are not fully resolved. The complexity of simultaneity conventions in different reference frames is also highlighted.
The latter. The Lorentz Transform does not apply to light as it does not have a frame of reference.kent davidge said:When people say that time measured from the Earth is equal to time measured from the Sun minus approx 8 min, are they taking into account Lorentz transformations or simply the fact that light takes approx 8 min from Sun to Earth?
kent davidge said:When people say that time measured from the Earth is equal to time measured from the Sun minus approx 8 min, are they taking into account Lorentz transformations or simply the fact that light takes approx 8 min from Sun to Earth?
Are the times equal?PeroK said:I'm not sure when people would say that and what they would mean by it. The Sun and the Earth are approx 8 light-minutes apart in the rest frame of the Solar system.
Which times are you asking about? Using the rest frame of the solar system, a flash of light that leaves the sun at time ##T## reaches the Earth at time ##T+8## minutes.kent davidge said:Are the times equal?
And vice versa. If you shine a flashlight from the Earth at the sun at time ##T+8##, the light will reach the sun at time ##T+16##. To reasonable accuracy, the situation is symmetric. Neither is "earlier" or "later" than the other.Nugatory said:Which times are you asking about? Using the rest frame of the solar system, a flash of light that leaves the sun at time ##T## reaches the Earth at time ##T+8## minutes.
The time measured from a clock on the Sun and the time measured from a clock here on Earth. Wont the NOW in the Sun be different from our NOW?Nugatory said:Which times are you asking about?
It is not very clear what is your question. Are you asking whether two identical clocks (one placed on Earth, second on Sun) tick at the same rate (as seen by an observer on Earth, for example)? The short answer is no.kent davidge said:Are the times equal?
If by "now" you mean the hyperplane of simultaneity selected based on an inertial reference frame where the Earth or sun is at rest then, to good accuracy, two such planes the intersect at the Earth "now" or at the Sun "now" will coincide all through the distance between.kent davidge said:The time measured from a clock on the Sun and the time measured from a clock here on Earth. Wont the NOW in the Sun be different from our NOW?
kent davidge said:The time measured from a clock on the Sun and the time measured from a clock here on Earth. Wont the NOW in the Sun be different from our NOW?
Using Earth's orbital velocity for v, that would be about 47 milliseconds -- if the relative velocity were parallel to the 1 AU separation. Since the relative velocity is perpendicular to the separation, the discrepancy in clock setting due to choosing between Sun frame and Earth frame is zero.PeroK said:Assuming a clock on the Sun and a clock on the Earth are 8 light-minutes apart in the rest frame of the solar system, then in a reference frame moving at speed ##v## relative to the solar system, the two clocks will be out of sync by ##8v/c## minutes.
jbriggs444 said:Using Earth's orbital velocity for v, that would be about 47 milliseconds -- if the relative velocity were parallel to the 1 AU separation. Since the relative velocity is perpendicular to the separation, the discrepancy in clock setting due to choosing between Sun frame and Earth frame is zero.
Right. Of course, gravitational potential (and orbital velocity) affects clock rate, not clock synch per se. The Earth clock may tick more rapidly than the Sun clock, but it will not be "early" or "late".lomidrevo said:But ignoring the difference in gravitational potential, correct?
You'll want to understand this in the easier case of flat spacetime (no curvature, no gravitational effects) first.kent davidge said:The time measured from a clock on the Sun and the time measured from a clock here on Earth. Wont the NOW in the Sun be different from our NOW?
kent davidge said:When people say that time measured from the Earth is equal to time measured from the Sun minus approx 8 min
m4r35n357 said:The Lorentz Transform does not apply to light as it does not have a frame of reference.
PeterDonis said:You are correct that light does not have a "frame of reference" (more precisely, you cannot construct an inertial frame in which a light ray is at rest), but that does not mean Lorentz Transformations don't act on lightlike vectors.
"Is massless" and "travels at c" are two ways of saying the same thing, because they are both ways of saying "the four momentum is null".nitsuj said:So does that mean it's because the light is massless is why it cannot have an FOR, not that it can go c.
nitsuj said:So does that mean it's because the light is massless is why it cannot have an FOR, not that it can go c.
PeterDonis said:"Massless", "cannot have a FOR", and "can go c" are all the same thing, so this question makes no sense.
The interaction between the light and the matter. You can't really treat light passing through a medium as separate from the medium. And the combination clearly has mass.nitsuj said:But light goes c when in a vacuum, not c through stuff, like air or water. what am I missing?
You can argue that position and you won't exactly be wrong, but it's not an especially helpful way of thinking about things. (If all or none of propositions A, B, and C must be true then it is logically sound to claim that A is true because of B not because of C but you aren't gaining any new insight; for that you have to ask why all three are true instead of false).nitsuj said:So does that mean it's because the light is massless is why it cannot have an FOR, not that it can go c.
Nugatory said:I can look at my wristwatch to find out what time it is NOW where I am; anywhere else, NOW means "has the same time coordinate as right NOW where I am".
Is it because when gravity is important, there's no way to choose a coordinate system such that arbritary points in space have the same time-coordinate? that is (x1,T) and (x2,T) is impossible?Nugatory said:You'll want to understand this in the easier case of flat spacetime (no curvature, no gravitational effects) first
No contradiction here, the statement about NOW meaning "has the same time coordinate" is always valid, but it easiest to see how it works in flat spacetime (because everything is easier in flat spacetime).kent davidge said:You say...But first you said...
. It's always possible to choose a coordinate system that assigns the same time coordinate to every event on any given space-like hypersurface.Is it because when gravity is important, there's no way to choose a coordinate system such that arbritary points in space have the same time-coordinate? that is (x1,T) and (x2,T) is impossible?