otacon14112 wrote: ⤴
Thu Mar 07, 2019 2:26 am
I was talking about the difference in time between when gravity was turned off, and the exact moment when the planet stopped orbiting the star and began continuing on its velocity...
There is no need to wait until light reached the observer, since there is no observer involved (there doesn't need to be a scientist hypothetically watching from an observatory in this scenario for us to know the unfolding event); this is a hypothetical situation in which you would instantly know, as if you were outside the universe watching the simulation (or whatever you want to call this hypothetical scenario).
Ay, but there's the rub. You're assuming that time is absolutely constant, and that just isn't so. Unless I've badly misunderstood you (which is certainly possible!).
(adding a tangent line reference is redundant, since velocity is a vector).
Habit from uni, where you really have to be specific about what's what. That said, it's not a bad idea to be specific here. Vectors aren't necessarily tangent to something.
I thank everyone for their input, but what does the acceleration rate near Earth (9.8 m/s/s) have to do with this situation? That unnecessarily adds more complexity to this scenario.
True -- I just got caught up with the other chaps' explanation of g = 9.8 m/s^2 and ended up typing a long and mostly useless blurb. I was so busy seeing if I could, I didn't stop to think if I should
I'd like to blame being so excited to talk physics for my going off on tangents
(pun completely intended).
trytip wrote: ⤴
Sat Mar 09, 2019 6:48 pm
time is a man made measurement value
Not really, no more than mass or length. Sure, we came up with techniques and units for measuring them (seconds, kilograms, meters). But if humans weren't around, wouldn't you still think that massive objects would exist, or that London would still be very far away from Sydney? The universal constants don't owe their existence to humanity.
Why should time be any different?
MrEen wrote: ⤴
Fri Mar 08, 2019 11:35 pm
The satellites your GPS use account for the gravitational time dilation because it's much less affected by gravity then us here on the planets surface.
This + 1000!
Relativity may not be easy to think about -- and for sure it's not a perfect or complete theory -- but it does a rather good job of explaining observations that would otherwise be unexplainable with our current knowledge. The precession of Mercury and other planets, our ability to see stars "behind" the Sun during an eclipse or "Einstein's cross" where massive objects can be directly observed to bend light, time dilation -- these are all unexplainable to the very best of my knowledge without relativity.
https://en.wikipedia.org/wiki/Tests_of_ ... relativity
trytip wrote: ⤴
Fri Mar 08, 2019 10:11 am
we can escape light and gravity, but never time.
I'm afraid we can't escape light (or rather, electromagnetic radiation) or gravity. There's no perfect insulator that can shield you from either.
The only exception would be a thought experiment where you imagine you're in a remote corner of the galaxy so far away from any object that neither light nor gravity have had time to reach you. If such a corner even exists, there's no known way for us to reach it -- by the time we travel there, even if we could
travel at light speed, light and gravity would have already beaten us there!
if you buy 1000 digital and analogue clocks of all sizes and mechanisms and put them in a row synchronize them to the second then let them run for a year, i do not believe they will stay synchronized which means time can't be measured
Isn't that rather a flaw with your measuring device rather than with time itself?
If I buy 1000 wooden metersticks and leave them out in the rain for a year, they won't all be the same length (or "synchronised") either!
If I buy 1000 palladium metersticks and place them in a carefully controlled environment, they'll probably all be identical even a hundred years from now. As it turns out, we have a pretty good "palladium meterstick" for time too. By measuring oscillations of caesium-133 atoms in a carefully controlled environment, we can get an extremely accurate device for measuring time.
https://www.timeanddate.com/time/how-do ... -work.html
trytip wrote:don't know what terminal velocity is on mars or jupiter but i'm sure it's much greater than here on earth
Less on Mars, greater on Jupiter -- if you ignore the effects of atmospheric resistance as you fall.
if you can affect decent and ascent with wings and engines, that has everything to do with gravity.
It has everything to do with forces
. The force due to gravity acts "down", the forces of atmospheric resistance or engine thrust act up. Take the (vector) sum of the two and you get the net force acting on you (and acceleration if you know your own mass). You're not manipulating gravity, you're just adding forces.
who came up with the measurement for an hour? or a day? man did looking up at the sun. once you leave earth's orbit you are in space time and the clock you bring with you is only relevant beneath earth's atmosphere
Ah, but you're only thinking about how time measurement can be conveniently defined. Sure, it was far easier for our ancestors to define a day as sunset to sunset instead of measuring ~3.309x10^13 Cs-133 oscillations. But that doesn't mean that 24 hours can't be measured both ways.
Time is not a slave of however we chose to measure its passing, just like the Great Pyramid has the same mass no matter if a tourist prefers to use kilograms or pounds.
I just remembered -- we have more evidence that time dilation occurs for objects approaching light speed. IIRC muons (or "mu mesons") from the Sun can be consistently detected here on Earth. But muons only live for about 0.2 seconds before they decay, while it takes light ~8 minutes to reach us from the Sun. Since nothing can travel faster than light, what's going on?
As it turns out, solar muons are traveling at close to light speed. Relative to them, they do only live ~0.2 seconds before decaying. But relative to us on Earth, they have survived 8 minutes. The only way both of these are possible is if they experience time dilation so that 0,2 seconds for them is 8 minutes for us -- and it appears that's exactly what's happening.
Therefore, time cannot be truly constant for all observers in all reference frames.