# NowThatWeKnow

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391

1. ## E=mc^2

Of course, we also have f=ma. Thanks folks, your only easy question this week.
2. ## E=mc^2

$E=MC^2$ $1 kg * C^2 = 8.98755179 * 10^{16} joules$ What is $8.98755179 * 10^{16} joules$ used for? Is this just a conversion from mass to energy or energy needed to accelerate it to a certain speed in a given time?
3. ## 1G Relativistic Rocket Ride, Wheeee

Exactly A starlight solar sail would be nice but it doesn't look like we should hold our breath waiting for that to be developed. We have a long time to go before this trip is made for several reasons.
4. ## Sharing the same "now"

That is the point being made by the twins paradox, the space twin does return to Earth's future according to the clock on the space ship. A 12 year 1G rocket ride for you would mean 100,000+ years will pass on Earth. Merged post follows: Consecutive posts merged Travelers would require a computer controlled time keeping system. There is no reason why you could not calculate Earth time while traveling. Just thinking out loud and not suggesting anything that would be practical.
5. ## 1G Relativistic Rocket Ride, Wheeee

I do not think changing mass from fuel consumption is considered in the numbers in my first post. You will notice it takes 2 years to reach .97c and then another 10 years to reach .99999..c . It seems that maybe the rocket accelerates slower and slower as the speed increases because of this so called relativistic mass.
6. ## scientist are still looking for zero temperature

Personally, I would just like to get a ball park reading off any thermometer with a large scale when 150 miles up and shielded from the Sun's visible light. Would other then visible electomagnetic energy have a large impact on the temperature? When the temperature of the dark side of the moon is taken you don't have to stick the thermometer in the moon's surface to get a reading, do you?
7. ## Einstiens Universe in 3 Trillion Years

Because all we remember is the "I before e, except after c" part and then not use spell check?
8. ## Sharing the same "now"

It could be instantaneous like a digital change. Using the theory of relativity you could calculate an exact time for every location in space and that could be used for a now time. Just like clocks for different time zones we could have clocks for different locations in the universe that would run at different speeds. They would be displaying a now time for different frames.
9. ## scientist are still looking for zero temperature

So what would a thermometer read in earth orbit if shielded from the Sun? -233C like the dark side of the moon? It sounds like space may not have a temperature but anything it it could.
10. ## Sharing the same "now"

Twin A's 2008 is twin B's 2009. So an event could happen in two different years yet happen at the same time or "now" as you say. You could demonstrate this after the trip was over. Each twin may disagree on the year of a recent event, but agree it happened 1 hour ago. However, from two different frames they will not agree. I can relate to your thought process but I am usually wrong.
11. ## scientist are still looking for zero temperature

That being said, would you take a coat or t-shirt if you were going to visit this hypothetical "void"?
12. ## scientist are still looking for zero temperature

Is there a thermometer that is not made of "particles"? I was just having fun saying you could not measure the temperature of a true void because it would not be a true void if something was there to measure it. I think some are implying that this "true void" may be outside of our universe. I am not disagreeing with you.
13. ## Sharing the same "now"

That isn't the way the story goes. The atomic clock, windup clock and biological clock all agree. http://www.phys.unsw.edu.au/einsteinlight/jw/module4_twin_paradox.htm You should read this site (insert your favorite word).
14. ## scientist are still looking for zero temperature

So if you put a thermometer in a true void, it would not longer be a true void?
15. ## blue shift galaxies

What about colliding galaxy clusters? I would think they should show a blue shift galaxy from out side their own cluster.
16. ## 1G Relativistic Rocket Ride, Wheeee

You mixed my merged reply to swansont and you together. I understand what you are saying. Merged post follows: Consecutive posts merged I stand corrected. I was considering the first 40% of the bell curve and not the complete curve. Making up my own definitions is not good.
17. ## scientist are still looking for zero temperature

Google found many online dictionaries. This on is not too bad. http://www.yourdictionary.com/ Wikipedia has too much info sometimes.
18. ## 1G Relativistic Rocket Ride, Wheeee

It isn't a bell curve? http://en.wikipedia.org/wiki/Lorentz_factor#Values So, would the acceleration of a constant Force rocket slow its acceleration as speed increased? And restarting the engines would be less then 1G? Merged post follows: Consecutive posts merged mass of the Moon * (the speed of light^2) = 6.61483812 × 10^39 joules. You will need a big rocket and please do not point it towards Earth.
19. ## 1G Relativistic Rocket Ride, Wheeee

I think tomorrow we will see a reply that says "the acceleration broke the symmetry". I need to think about that I guess.
20. ## 1G Relativistic Rocket Ride, Wheeee

This math agrees with you I think: p=y(rest mass)v ---- density=time dilation(rest mass)v but If you are at rest in your inertial frame, who is to say what your speed is. Why couldn't the length contraction you see come from the objects around you moving and not you. This keeps coming up to haunt me like the twin paradox. Whoever did the initial accelerating is moving but that makes no sense to me in a metric without an ether.
21. ## scientist are still looking for zero temperature

Degree - English 1. A unit division of a temperature scale. 2. A unit of latitude or longitude, equal to 1/360 of a great circle. 3. Relative intensity or amount, as of a quality or an attribute: a high degree of accuracy. And it doesn't stop there.
22. ## 1G Relativistic Rocket Ride, Wheeee

The "Greek letters used in mathematics" link helped some. I will post a list I started in my next post hoping people will add to or make corrections. Thanks Merged post follows: Consecutive posts merged What I think I am seeing (here and your other Force link) is Force required to accelerate is somewhat proportional to time dilation. Time dilation becomes very nonlinear (like a bell curve) as relativistic speeds are increased. 1a. Is that right? 1b. The acceleration of a constant Force rocket would slow its acceleration as speed increased? 2. At any point the engines were shut down the rocket would become an inertial frame and maintain speed relative to its surroundings (not counting space dust and gravity influence)? 3. Why couldn't you restart the engines and accelerate out of your inertia frame? I started a list. If anyone sees any errors or would like to add to it please feel welcome. p = Density P = Momentum Y = Lorentz factor t = Proper time T = Time in another frame c = Speed of light u = velocity as observed in the reference frame where time t is measured v = velocity V = Volume F = Force G = Gravitational constant m = Mass d = Distance a = Acceleration
23. ## General Relativity stress-energy tensor

Yes I did look at wikipedia but after this thread it makes more sense to me. Thanks for your succinct answer. That is exactly what I was looking for when I started this thread.
24. ## 1G Relativistic Rocket Ride, Wheeee

That might work if I can find the right one. A glossary of the characters used in these equations would also be nice. I need to get up to speed on math if I am going to keep playing this game.
25. ## 1G Relativistic Rocket Ride, Wheeee

2 hours and 4 minutes, not too bad. (you know I appreciate your help) Some of that math I could probably actually do but my first problem is I do not know what each character represents. It wasn't in my "Relativity for dummies" book. I have figured out a few but is there a complete list some where? Sorta like c = speed of light v = velocity V = volume ?? funny looking Y = ?? Should I be looking at this problem like E=MC^2? The faster you go, the more energy it takes and that is why it isn't linear? I keep thinking that at any time you shut the engines off you would be at rest and inertia would keep you going. Starting your engines again would quickly get you to 1G acceleration. Sort of like starting over again. Arn't you either at rest or accelerating? Even when the math is done it only gives you an answer and not a good visual of what is happening or why. Thanks Merged post follows: Consecutive posts merged You speak my kind of math. Are you saying that less spinning and equal spinning would produce the same results (constant velocity)? And more spinning is needed for acceleration? When you take all resistance away it would seem that more spinning would not require additional force, just a higher gear. I guess the part that confuses me is I see everything as at rest in space so force would be force. How else can you look at it in a metric without an ether? If you have any comments on the post above this one I would appreciate it. I relate to your words and appreciate it. I have my good areas but formal training in physics is not one of them, as you can tell.
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