NowThatWeKnow

OK asprung, does this sound about right? There is no reason why time can not be constant giving us an absolute time and a universal "now" as you propose. It is not the duration of a time segment that changes as you accelerate, but it is how fast you are moving through spacetime that impacts how you measure it. To support this, a good example would be a 1 G rocket ride accross the Milky Way. The duration of time is not changing but you are traveling through/accross time. This will allow you to travel 100,000 light years in just 12 years of your life while 100,000 years pass in universal time. How else would this be possible with out breaking the speed of light? A similar deception of time occurs when spacetime is curved because of gravity. It is not the duration of a minute that changes put only how you perceive and measure it. So universal or absolute time is measured in flat space while not moving relative to the CMB and everyone can share the same "now".

It would be about as useful as the last four post in this thread.

Is it possible that large orbiting masses may be able to maintain heat from movement created by tidal forces?

Darkness moving is no more out of line then space expanding IMO.

Youtube, like SFN, can be a source of good information or garbage as we witness here daily.

Yes, that is what I said in post #8.

So what is the duration of "now"?

What you said along with what you didn't say did not make what you believe clear. I was just asking a question. Your post edit did shed a little light on your statement. So, do you believe there is a universal "now"? I guess you could stack the different length "now" time segments like a pyramid with them centered on each other and consider that simultaneous.

We can measure how fast darkness appears or disappears. You can move towards or away from a state or condition and darkness is a state or condition.

Why would we have to establish a universal now in order for one to exist? Two locations can share the same time without human intervention. That would be like saying the speed of light is what it is only because we know what it is. My problem with asprung is that he is saying only certain laws of physics carry over to different frames. Also the length of "now" has not been defined and would have a margin of error regardless of its duration.

Centripetal is real and centrifugal is an apparent force. Using a satellite as an example, I see centripetal force as gravity and centrifugal force as inertia keeping the satellite going straight and resisting orbit decay.

I am not sure if you or anyone else is still following this thread but here are a few thoughts from a layman. Corrections are always welcome from the experts so we all can learn. Space, time and the speed of light are all necessary pieces of the puzzle and must follow certain rules for special relativity to be mathematically correct. However, there are many paradoxes associated with special relativity. "Einstein postulated that the speed of light in free space is the same for all observers, regardless of their motion relative to the light source." I look at the speed of light as being constant, but only relative to its current location or frame. As light leaves the Sun headed for open space it would actually speed up as gravity decreased IF it could be measured in real time from a single frame like Earth. Since we can not see the light until it gets to us we can only measure what we see relative to the speed of clocks in our frame. Therefore we measure the speed of light at 186,000 miles per second. If we we were closer to the Sun our clocks would be running slower so the slower light would still be measured at 186,000 miles per second. I look at it like gravity bends space so light has further to go in gravity but your clock is running slower so the math works out. In special relativity the time dilation (and length contraction) comes from speed rather then gravity. you will observe the speed of light from any source as being constant. The light from a flash light in your hand or a flash light on a ship moving at relativistic speeds will be seen by you at the same speed. You would observe the light from the ship and the ship itself separating at a speed much slower then light as they both traveled at a speed close to each other. The guy in the ship would see his light moving away from him at the speed of light because relative to his very slow clock it would be moving at 186,000 miles per second.

Keep in mind that the expansion is not from the edge out, but is uniform. The expansion is also measured much closer to home so the horse is not all that far away. Since there is no reason to believe we are at the center of the universe we could represent what is happening everywhere.

I can not see one without the other so you are on your own. As mentioned, you have an "uphill battle".

I can relate to what you are saying I think. At any point of time in one frame there is a simultaneous event happening in other frames, even if we do not observe it. One problem would be that a one second event in one frame may be a 10 second event in another frame making it unable to happen at the same time. It seems you would have to use a very high resolution of time and then just call it close enough.

That may depend on what definition of "dark" and "move" you use. Does a shadow move? I probably should have put a smiley with my post as I was having fun with what some would think a silly question.

iNow, It would seem that true simultaneity could only happen in the same or identical frames. Since that is almost impossible, a range of error is necessary to use the word. It seems that asprung allows for more error then most and may not be that far off, at least in his mind. When I read your post I see you well ahead of me in most areas of physics. Edit - Plus, Swansont and Martin correct my post often and yours rarely.

Excellent link and got a bookmark. While relativistic speed may show the "simultaneity concept rather well", Here on Planet Earth we have a huge variable frame caused by general relativity. We don't let that stop us from defining simultaneous events. At what point does time dilatation or length contraction cause a problem in defining simultaneous? Could we say that when the front of the train passed the end of the dock my right foot hit the ground and call it close enough?

Light and darkness travel at the same speed. This can be observed when turning a light on or off.

During acceleration away from Earths frame your clock will continue to run slower and slower as you accelerate. When you shut off your engines and become an inertial frame moving away from Earth your clock will maintain a ratio of running slow. As you decelerate back to Earth's frame your clocks will speed up until they match the speed of Earth's clocks. The same thing happens on the way home. Does that sound right Swansont?

You can't go the speed of light but at relativistic speeds the distance from the Earth to the Sun would be covered in seconds, not minutes. You would also age only seconds. This would be because of time dilatation and length contraction.

Hi Norman, I am in over my head and I am definitely not answering for Martin. Don't most agree that GR will require some tweaking for simultaneity when considering some of the large distances in cosmology? It seems like I was reading about that somewhere.

Relative to Earth? OK. Accelerate away from Earth to .99c and shut off your rocket engines. While traveling away from Earth at .99c, send a second rocket from your rocket pointed away from Earth and have it accelerate to .99c. You will see yourself moving away from Earth at .99c and the second rocket moving away from your at .99c for a combined speed of almost twice the speed of light. However, from Earth the second rocket will be moving away from Earth at just under the speed of light. Your example is frame mixing and that does not work. Each frame has its own time dilatation and length contraction conditions and should not be mixed. Relative to you, light will move at c. The only exception is using the expansion of space to separate faster then the speed of light.

Light speed is independent of the motion of the source. Relative to you, your light will travel c in any direction. You can think of it as you are standing still and everything around you is moving.

Don't quit thinking yet. There are several in these forums that say the light is really not slowed down or stopped. That is why I started my last post with "Most of the experts around here will argue that light can not be slowed down but the average speed can be slowed down as it passes through different substances. The light is absorbed and then re-emitted with a delay coming while it is absorbed." There is a thread about all this somewhere around here not far away.