Robittybob1

There are already huge compression forces inside stars and planets just waiting for the day that gravity seized to exist.

There would still be the Van der Waals forces to overcome.

Very interesting. Worms or beetles storing up food for themselves. I like the concept.

Do you think that is a bit sexist? Men fart but women just pass wind.

That's why I quoted it.

Thanks for that Latest from Wikipedia is:

You wanted to know if Relativity can be aligned with Quantum theory and as I said 3 dimensions of time is said to allow this. Does it really matter how many dimensions time has?

Where did that figure come from?

I have seen papers which suggest 3 dimensional time unifies those two theories. I'm just not good enough with the math to know whether that is really true or not.

If it was random there should be the same chance of getting each number. have you graphed the frequency of each number? I ran a macro looking at the random generator in Excel 2007 and over 300,000 events each number 0-9 was chosen very evenly. "4" seemed to be a little light at 259 less than the average of 30,000 per number. Next 300,000 throws and it caught up.

From Wikipedia on GPS Hence the GPS satellite clocks gain approximately 38,640 nanoseconds a day or 38.6 μs per day due to relativity effects in total." With Bob and Alice thought experiment the speed of the spacecraft will be the dominant effect so the slowing of time due to gravitation, as Bob approaches the Earth, will not be significant at the speed Bob is going (0.6 c).

I know a cheese sandwich can be pretty darn good.

Is this due to different meanings of "nothing"?

Getting close though.

There are other things to do. Wish him well.

An inte Yes it is just one more of the many factors to consider when trying to comprehend relativity. A very interesting connection came up on another forum today and that has been confirmed by an internet search, and that is "the time dilation caused by gravity on the surface of a planet is equal to the time dilation for an object moving at the planet's escape velocity". So that said in another way is that the velocity that an object will gain by free falling into a gravitational field will be the velocity that will cause the same amount of time dilation as that object has while stationary in that gravitational field. I wonder if I said that correctly, but it is such a new and not widely discussed idea (I could be wrong about that too, but I had not previously heard of it in the 4 years I've been on the science forums.) "Since gravitational time dilation is tied to gravitational potential, and escape velocity is the speed at which you need to start with in order to climb to infinity against Earth's gravity with a ballistic trajectory." Very interesting that escape velocity and time dilation are linked and not just for things falling into a black hole but everything under the influence of gravity.

I'm sure I've heard an expression like that before. It may have been slightly different. Would "because they travelled faster through space, they travelled slower through time" rather than "because they travelled further in space, they travelled less in time", be correct? (Minkowski spacetime diagrams)

Going back over the threads in this forum on relativity this post struck me as being filled with wisdom: http://www.scienceforums.net/topic/82735-special-relativity-twins-paradox-is-it-real/#entry801650 I like that concept. Next post it was considered incorrect - oops!

Bob and Alice had been over the years pre-flight discussing Relativity on the NASA approved science forums and had noticed one glaring mistake. There were these diagrams and animations of time clocks on board another craft where it was possible for both observers to see the workings of each other's time clocks. Many presenters had it so that one observer who was thinking his/her time wasn't dilated ending up observing the "one" photon traveling in a different direction as someone observing the same photon in a time dilated situation. Now in the words of Janus that is a "physical impossibility". Bob and Alice had to work out a method so that in both situations the moment of reflection was always the same time, yet one photon seemed to be traveling a different length of path, if light speed never changes, and there is no length contraction in dimensions other than the direction of travel, so how can that be comprehended? In clocks that have been calibrated, a moving clock will be showing slower time. But then can the person on the moving craft also look across and claim that the other guy is moving and their clocks are slowed? Could that be "Yes, they are slowed but never slower than his"? Both Bob and Alice are still confused. Muons are so interesting.

So the two parameters that were agreed on pre-flight were: 1. The time intervals between the pulses, and 2. That Bob would send an additional signal 3 ms after receiving a pulse from Alice. The time between the pulses for Bob was set at a shorter interval for it was known that his clock would be running slow compared to the calibrated master clock at Houston. Alice's clock onboard the ISS will also be slightly time dilated compared to the Houston one but not by any significant amount. Alice has already received a time dilated signal back from Bob so their prediction that Bob's time will be running slow has been verified. Bob has just a split second to decide when to action his LiDAR pulses to check his velocity, Alice is anxiously waiting to detect these pulses. She hoping all is well and Bob hasn't run into any space debris or valuable assets for they had been pre-warned it was a dangerous and foolish place to run speed trials considering the number of satellites and the vast amount of space debris orbiting the Earth. She knows there shouldn't be too many issues with the first pulse for as far as they are aware there are no satellites orbiting the Moon at the moment.

"It is very simple to show that you cannot do away with length contraction by having the frames measure their relative speeds differently." Well that is the purpose of the experiment, to find out whether this is true. "All it takes is one LiDAR pulse" I disagree with that as LiDAR takes two pulses to make a speed measurement. The rest seems to be the confusion between reading other peoples clocks while you are very distant and moving relative to each other. Alice and Bob don't know what time it was when the pulse is fired unless it was preplanned while they were calibrating and setting up their machines.

It is unreasonable to be hard and fast about not saying Bob is heading toward the ISS for he well knows he started off from stationary on the Earth some weeks ago and he headed out, stopped, turned around and now is heading back to Alice that he knows is/was stationary when he left. He also knows that as he sped up his time was be dilated. Even though he knows he is moving he finds it is so easy to view the situation as the Earth and the Moon speeding up towards him. He had been taught classical relativity and very easily slips back into that mindset. Nothing short of a catastrophe would made the Earth and the Moon change direction so right or wrong he finds himself thinking he is moving. And I tend to agree with him.

Janus - I appreciate that someone is reading it. What I would ask you to do is, please, is it possible you work with 0.6 c rather than 0.8c because then I will be able directly compare your answer with mine (that I'm working on)? The only other thing I am trying to imagine is that at all times we talk of the situation from the perspective of the person doing the measuring, so I wouldn't say like you seem to have "Bob fires off a pulse towards the ISS as he passes the Moon and when his clock reads 0. It takes ~1.282 sec for that pulse to reach the ISS. In which time, Bob has traveled ~ 231,000,000m and is now ~153,000,000 m from the ISS. The pulse bounces back towards Bob at c while Bob continues to travel towards the ISS at 0.6c and they meet in another ~0.32 sec." From Bob's perspective the ISS is coming toward him, not him going toward the ISS. Also are your clock times corrected for time dilation? Can Bob use the signal from Alice as the time to turn on the LiDAR? Bob first senses Alice's LiDAR when he is at the Moon distance from the ISS, 0.3 ms after the LiDAR will sent the first pulse, it has been figured since the things ahead are coming toward him at less that the speed of light, there should be some point where two pulses can be fitted in, but it has to be done in less time than the travel time for Bob to the ISS (1.709627176 sec) 1.7 seconds doesn't seem enough but the light waves will hit the ISS at a position, well somewhere in between, but where and when. If light is going at the speed of light out from Bob and Alice's ISS was able to travel at the speed of light toward bob the reflection would have been at the halfway point, so if at the speed of light it is half way, at 0.6 the speed of light (or thereabouts (doubt)) one could imagine the reflection being at 0.6 the distance to the half point. As the signal returns to Bob's LiDAR Alice keeps on approaching, the light will take the same amount of time to return. [some replies have come in so I'll break and read them. Dratt! One of them was my own.] @ Janus - what I find difficult is to read someone else's figures and make instant sense of them, I'm using an Excel spreadsheet where all graduations of speed can be analysed (I am increasing the relative velocity by 0.01 c at each step) So once I have got my head around how to do the calculations of when to fire the LiDAR I will be able to tell where you and I see the issue differently. What I need is the logic to work out the steps so I can enter the formulas into the cells. Note: Bob and Alice can't read each other's clock and the firing times have to be preset. So statements like this are forbidden "But wait, by the ISS's observations, only 1.28 sec ticked off for Bob between sending and receiving the pulse. This is an physical contradiction."

There are endless variations but for Bob's view of the situation when Alice recorded Bob doing 0.6 c we have the following. The 3 millisecond pulse return was measured by Alice as having dilated to 3.75 ms which is consistent with a clock moving at 0.6 c. speed in C => 0.6 c (as recorded by Alice) beta=v/c => 0.6 gamma = 1/sqrt(1-beta^2) => 1.25 speed of light m/s => 299792458 Earth Moon distance m => 384,400,000 m Bob's time (dilated by gamma) (travel time in sec get less as speed increases) => 1.709627176 s 3ms time dilated by gamma (in milliseconds) => 3.75 ms (as recorded by Alice) Now to try and work out Bob's relative velocity as measured by the LiDAR on board. Now Bob can see the ISS straight ahead, the Moon is to the left and the Earth will be to the right as they pass by at an estimated speed of 0.6 c. Bob has his doubts about what he will measure as his own relative velocity as for he has surmised that since his clock was calibrated against Alice's clock and Alice recorded his relative speed at 0.6 c the onboard clock will be time dilated as he had to change direction and reapply the thrusters to regain top speed (he is well aware of previous acceleration). This was previously discovered by Bob's grandfather, one of the travelling twins, (the so called Paradox Twins) and they ended up different ages because the symmetry was broken. (It was rumoured that the cosmic radiation got to him in the end so he tragically died sooner than the older twin.) Now Bob has to figure out when to turn on the LiDAR to get two pulses recorded before the ISS passes to the right. "Bob's time (dilated by gamma) (travel time in sec get less as speed increases) => 1.709627176 s" what that means is that since Bob's clock has slowed down it will take fewer of his seconds to go from the Moon to the Earth, so by his calculation of velocity = distance over time, his velocity is greater for he covers the same distance in less time. Because the trip will take less time he has more issues with fitting it all in. Bob's LiDAR has been pre-adjusted to fire at an interval of exactly 2 seconds (That is like 2 ticks of the clock) so it is irrespective of how fast the clock is moving. Remember to Alice Bob's clock is ticking slower so those 2 seconds is measured by her as been dilated by gamma, so 2 seconds of Bob's time measures 2.5 of Alice's Earth seconds. [if we can do without length contraction to worry about a position in space measured in meters is the same place wrt all parties. I'll leave it there for a day or so and think it through. Merry Christmas folks. ]

It seems if the light pulses have a delay for 2.6 seconds the pulse will be out there near the Moon and the reflection back at the ISS in time to put up another pulse even at the higher relativistic speeds. Plenty of time is available at the slower speeds but will the effects show up? It might be a couple of days before the maths is completed - Christmas you know! Do we all agree that the LiDAR on the craft returning from the Moon's direction will be time dilated? So even though the ISS positioned LiDAR will be set on 2.6 second pulse delay, the one on Bob's craft will need pre-adjustment. But we need to know ahead of time by how much for we will only get one run at this before Bob is off to Alpha Centauri. http://en.wikipedia.org/wiki/Alpha_Centauri If Bob's LiDAR was set up such that 3 ms (calibrated on Earth, but dilated at speed) after receiving a signal from Alice it would activate a pulse, this way it is known that the photons will travel back to the ISS at the speed of light so the time difference will indicate the magnitude of gamma .