Recent content by JArnold

The underlying reason for time dilation is real-world physics. With relative uniform motion it is observer-dependent, and yes, there is no “actual.” With gravitation and inertial acceleration different clocks actually move at different speeds, and one twin will actually age more than another...

You seem to have your own dictionary. "Velocity" doesn't substitute or include "speed" and "rest"; velocity is speed in a particular direction, and a body that is considered to be at-rest thereby has neither speed nor velocity. A clock-speed that can be considered more-or-less dilated from other...

"Time dilation" is a standard term. "Actual" is not-relative, and can be measured variously from different reference frames.

I think I agree. Uniform velocity, speed, and rest are relative. Whether a body is inertial or accelerating is not. Yes?

Actual time dilation is "actual" when A observers the clock of B moving more slowly, while B observers the clock of A to be moving more quickly. It is not actual when each observes the other's clock to be moving more slowly. Force causes time dilation because it causes acceleration, and time...

Velocity is just motion in a particular direction. Inertial motion isn't relative? Don't tell Einstein.

I'm just joining this long discussion, and it may be inevitable that my contribution will only be annoying. But there are basic and well-established principles that should guide the discussion: Uniform motion is relative; inertial acceleration and gravitational effects are absolute. In the...

Weightlessness can be determined by placing a drop of electrically neutral liquid in the center of a transparent sphere. If it remains in place, everything stationary relative to the drop is weightless. If the drop appears distended, there is a tidal influence present, indicating that there is a...

The equation for cosmological redshift where z << 1 is is commonly given as z = λobs / λemit -1 What is the equation for high-z, accounting for how light surpasses the spatial expansion it leaves behind, but abstracting from gravitational influences? I'm particularly interested in how CMB can...

That's fine. But if redshift doesn't scale linearly, neither does CMB "temperature", given by Tobs = Tem/(1+z) in the original thread.

That thread wasn't helpful. I had specific questions, and I believe my calculations were correct. Here's another strange calculation: The spatial expansion between 13,750 Myr and .38 Myr would be 36,184 -- not 1100.

The earlier thread was closed for some reason. It prompted this question: Given the formula for CMB temperature Tobs = Tem/(1+z) (analogous to the formula for z) it seems the age of the universe at the emission of the CMB would have been about 12.5 Myr (if 13.75 Gyr presently), not 380,000...

I can understand using both, and that all extreme distant measures are more or less inaccurate. But to go from distance modulus to Mly is only to go from 2 digits to 4 or 5, and though a LOG10 might reduce relative inaccuracies (only because it's a LOG10 reduction), to telescope relative...

Why do astronomers and cosmologists prefer to use the Distance Modulus instead of -- rather than in addition to -- Bly (billion light-years) or Mpc (mega parsecs)? Being a LOG10 it distorts relative distances. You can find Bly plotted on a graph (but not specified), and even in studies comparing...

Jorrie, thank you for your patience. I was wrong, you were right. What finally made sense to me was a thought experiment (in the shower!): If the universe were to abruptly stop expanding, would a distant galaxy still recede, and have a redshift? The answer of course is no.