NowThatWeKnow

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1. 1G Relativistic Rocket Ride, Wheeee

And in my head. As long as there is thrust pushing the rocket it will accelerate in the vacuum of space. Inertia says a body in motion will stay in motion in a straight line unless acted on by an outside force. So if there is thrust (outside force), the rocket will continue accelerating towards the speed of light but never make it. There will be no forces acting on the rocket except for the thrust (discounting space dust and gravity). So newton's theory of action and reaction fits well. Where are the experts??
2. 1G Relativistic Rocket Ride, Wheeee

I would think in the vacuum of space a constant thrust could provide a constant 1G. Could someone elaborate on that please? I totally agree if you hit something at relativistic speeds there will be a lot of energy created.
3. centrifugal force

I understood that centrifugal force is an "apparent" force that is directed away from the center, but it is actually inertia telling a body in motion to stay in motion in a straight line.
4. General Relativity stress-energy tensor

I knew it could be put into English! Thank you for coming out of your rubber room (compliment) to help me. It is Saturday night and time to chase a little skirt so the "cosmic vacuum" will have to wait. Thanks Norman
5. General Relativity stress-energy tensor

The stress energy tensor, $T^{ab}$, is the gravatational attraction of matter considering MOMENTUM and ENERGY, and also circulations... and the kitchen sink. Am I making progress?
6. General Relativity stress-energy tensor

Lets make sure I understand each character: c=speed of light v=volume and not velocity $\rho$ = mass density (Different then just mass in KG? how is this determined?) $T^{ab}$ What does this represent?
7. General Relativity stress-energy tensor

I do not mind some math (like Norman used) but what I usually get is an equation with a bunch of characters that are not defined plus the goal is also not defined. Here is what I was looking for to get started but corrections will be needed of course as I do not know the facts or I would not have asked the question. Example answer: GR has to do with gravity, but unlike Newton who used only mass, GR will consider things like density and volume to...P=m/v with p=density, m=mass and v=volume....and then we... See what I am looking for? But lets start with- The first question is: What is the stress-energy tensor going to tell us when we do the math? The gravitational attraction of certain matter?
8. General Relativity stress-energy tensor

I have been trying to grasp the basics of "stress-energy tensor" and most information I have found starts above my head. I hope the basic concept can be put in English words without a ton of complicated math. It seems like more then just mass is being considered in GR when calculating the curvature of spacetime. Is that what it is all about? Links and explanations welcome.
9. How many stars do dwarf galaxies have?

It seems that local gravitational forces causes many galaxies, and even galaxy clusters, to collide. However, after a certain distance away, the expansion of space makes sure all galaxies are moving away form us.
10. Frozen earth

Wouldn't that be like freezing a beam of light? It may take absolute 0 -1
11. what is the universe expanding into?

Hey, I started with "Even if". Isn't that worth something? Some of your post sound like NowThatWeKnow and that makes me go aaaarrrrgh!
12. what is the universe expanding into?

I like that calculator better. At first I thought they left out "z" but then I saw it at the top. Even if the Big Bang was an explosion of singularity or a region, it seems it is not driving what we observe today. Maybe the BB ran out of energy and something else took over the expansion.
13. what is the universe expanding into?

Airbrush, Martin pointed me to a really neat calculator that helps put things in perspective. http://www.astro.ucla.edu/~wright/CosmoCalc.html The light from a galaxy that took 12 billion light years to get here started towards us when it was only 4.8 billion light years away. That galaxy is currently 23.58 billion ly away. The space the light traveled through had an expansion rate of 4.9. If you are interested, a few simple rules and definitions are needed to understand the calculator. If you put 3.9 for a value of "z" and click "flat" you may see where the #'s come from. The light speed episode of "the Universe" program said "the only thing faster then light is the expansion of space. This may be the answer to the question. Also, a third party seeing two objects separating at faster then the speed of light does not mean those two objects see themselves separating faster then light. That crazy space math. http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html and http://www.cthreepo.com/cp_html/math1.htm
14. i still dont understand how someone can "escape"time by traveling faster than light.

Do a google search for "faster then light speed" and you get all sorts of stuff.
15. Toy model space that is not expanding into

I try to think of space/time as a single construct. As time passes it stretches the metric of space with it. It sounds like you are implying that maybe space is not expanding. Would that require time to continually speed up for us to observe the expansion we see? It is hard enough to understand with out illusions making it even harder. It is probably just as hard to imagine a finite universe with a boundary we can not cross as a infinite universe without a boundary to cross.
16. Toy model space that is not expanding into

I was hoping to get ajb to elaborate on "Then we see that space gets larger as time does, yet it is expanding into nothing." What could be closer to nothing then a vacuum that is void? Not having a surrounding woud be easier to visualize if we observed a static universe but that is not the case. Our observations show that the distance between matter is expanding. Maybe it is not expanding into anything but is expanding through nothing. None of us know for sure what is happening and it would be foolish to rule out any of the many possibilities. We all just put a different likelihood on each scenario. your knowledge allows you to grasp what you say much better then my knowledge allows me to grasp what you say. However, my respect for your knowledge tells me to give your views much consideration and I listen when you speak. Now, if someone would get off their double sided end and figure out the real answer.
17. Toy model space that is not expanding into

Do you think it is possible that time is responsible for the expansion of space? Maybe time could be a type of ether. It seems the universe is a vacuum full of matter and electromagnetic radiation. Is it expanding into a vacuum that is void?
18. i still dont understand how someone can "escape"time by traveling faster than light.

The twin paradox: Is the symmetry of time dilation paradoxical? http://www.phys.unsw.edu.au/einsteinlight/jw/module4_twin_paradox.htm
19. i still dont understand how someone can "escape"time by traveling faster than light.

Actually, only electromagnetic radiation (like light and radio waves) can move at the speed of light because the photon has 0 mass. All matter is restricted to speeds below this. This short power point presentation may help you understand time dilation. http://faraday.physics.utoronto.ca/PVB/Harrison/SpecRel/Flash/TimeDilation.html Also my thread in "relativity" "1G relativistic rocket ride Wheee" gets into it a lot.
20. what is the universe expanding into?

The thing is, it is possible that you are not wrong. Have you heard any one here that had the answer? You are doing fine for 15.
21. 1G Relativistic Rocket Ride, Wheeee

According to the light speed episode of "The Universe" program on the History channel, .99c woud give you a very distorted view directly in front of you and you lose the distance advantage to the side. That program and these forums in the last 30 days is my total experience with relativity. But I do like to give my opinion. And I did stay at a Holiday Inn Express the other night.
22. 1G Relativistic Rocket Ride, Wheeee

After you looking at my questions I am sure you do not want me answering your questions. My question is have we actually observed anything moving close to c that had transverse movement? Edit - You bring up a very good point. The edge of our known universe would be very close at .99c.
23. 1G Relativistic Rocket Ride, Wheeee

I have "simultaneity at a distance" when I run these scenarios through my head.

Twins
25. what is the universe expanding into?

When my parents were young the Milky way was the known universe. Today that 100,000 ly has turned into 13 billion ly. The expansion of space and the speed of light keeps us from seeing any further (at this time). I do not see it as laziness.
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