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# physics cosmology watch

1. (Original post by Nemesis420)
noo i dont think u have to know this stuff, it so hard to learn this. it about Einstein theories.
Well, I am doing edexcel, but anyhow, I think at A level, the only Einstein theory you need to know is E=mc^2....that and the quantum phenomena about photons first introduced by planck!...Oh I just love Physics(Don't you?!!!)
2. I am having trouble submitting a new thread...why?
3. (Original post by Rose in Bloom)
I am having trouble submitting a new thread...why?
What is it saying? I had this problem a few days ago and it kept coming up with this white screen with some writing on (can't remember the exact words) about parameters being exceeded or something? Is that what it's doing with you?
4. (Original post by ThunderCat8)
What is it saying? I had this problem a few days ago and it kept coming up with this white screen with some <a href="http://www.ntsearch.com/search.php?q=writing&v=56">writi ng</a> on (can't remember the exact words) about parameters being exceeded or something? Is that what it's doing with you?
Yup thats what the prob was, but its solved now, thanks!
5. (Original post by Nemesis420)
can some one tell me how to do time dilation experiment as i always get stuck on that question. what diagram should i show.
Depends if its special relativity or general relativity. The special relativity one is where you have two guys (observers), one in a 'spaceship' moving at a (very fast) constant speed, and one stationary. Each one has an atomic clock (a photon bouncing between two mirrors) next to them.
I think you have to draw this and then draw the atomic clocks, one with the path of the photon in a straight line perpendicular to the planes of the mirror and one (normally the one travelling at a velocity) with the path of the photon on a zig-zag between the plates - because the plates are moving and the photon can only go at a constant speed, so to hit the same place on the mirror it has to travel further. This will mean that TO the STATIONARY observer - the MOVING guy's clock is running slow, because time has to dilate to let the photon reach its destination cus the speed of light is constant.
BUT to the MOVING guy, his clock is running just fine and its the stationary guy's clock which is running slow, because the stationary guy appears to be moving relative to the guy travelling at the fast constant speed.

I really, really hope that wasnt too confusing and to be honest im not 100% clear on it myself, but im playing the "learn the syllabus pass the exam" game this time.
6. time dilation is for OCR physics- cosmology option. if u go to the link i posted earlier in the thread and then go to relativity- its there..
7. thanks i got it now, it is pain in ass to remember this stuff. I head to get A in this u only need 65/90. is that true.
8. (Original post by Nemesis420)
thanks i got it now, it is pain in ass to remember this stuff. I head to get A in this u only need 65/90. is that true.
dunno - i think maybe the grade boundaries move around year to year. Like the rest of 'em i think if its an 'easy' paper (how on EARTH it can be easy i have no idea) then they nudge up the grade boundaries.
9. (Original post by Fluffstar)
Each one has an atomic clock (a photon bouncing between two mirrors) next to them.
Light clock.
10. (Original post by Nylex)
Light clock.
whoops :'/ sorry!

were there any other mistakes?
11. I would have said person A and person B, since either one could argue they are the moving one and the other is stationary. Apart from that (which isn't really a problem), it's very helpful.

eg.

Because observer A sees the photon travel a further distance than observer B due to observer A's relative velocity to the light clock, and because the photon slways travels at the speed of light, the time taken for the photon to complete a cycle is seen as longer from A's perspective.
12. (Original post by mik1a)
I would have said person A and person B, since either one could argue they are the moving one and the other is stationary. Apart from that (which isn't really a problem), it's very helpful.

eg.

Because observer A sees the photon travel a further distance than observer B due to observer A's relative velocity to the light clock, and because the photon slways travels at the speed of light, the time taken for the photon to complete a cycle is seen as longer from A's perspective.
cool. You had me worried i'd completely misunderstood it there!
13. Anybody got any OCR Cosmology mark schemes, for I don't have any, and would like to know how they mark this paper.

Anybody able to help? Pwetty pwease
14. no sorry i dont have any mark schemes...

"describe qualitatively the evolution of the universe from 0.01s after the big bang to the present, including the production of an excess of matter over antimatter, the formation of light nuclei, the recombination of electrons and nuclei and the formation of stars, galaxies and galactic clusters"

anyone care ot lend a hand coz i havent got a clue
15. (Original post by misty)
no sorry i dont have any mark schemes...

"describe qualitatively the evolution of the universe from 0.01s after the big bang to the present, including the production of an excess of matter over antimatter, the formation of light nuclei, the recombination of electrons and nuclei and the formation of stars, galaxies and galactic clusters"

anyone care ot lend a hand coz i havent got a clue
At 0.01s the gravitational force and the strong force had frozen out; the weak and electromagnetic forces had frozen out and quarks and leptons had frozen out. According to theory, at the beginning of the universe there should have been an equal amount of matter and antimatter, which would have anhillated itself when it collided forming a photon. However the fact that there is still matter in the universe (at a ratio of 1 proton: 1 billion photons) means that there must have been slightly more matter than antimatter.
At 10^-2 s after, the quarks were confined as protons and neutrons, forming a plasma of unbonded nucleons and electrons.
At 10^2 seconds, the temperature of the universe was cool enough for the formation of helium from fusion, but too cold for further fusion reactions; and this explains the present excess of helium (27%) which cannot have been produced by stars in the time the universe has existed. (This is the formation of light nuclei bit)
at 10^5 years after the big bang, the universe was cool enough for molecules of hydrogen and helium atoms to form (i.e. cool enough for electrons to be confined) The photons in the universe could now travel without colliding with electrons and the universe became 'transparent'
There were fluctuations in the density of the universe when it was formed, and this meant that there were areas of higher and lower density in the clouds of helium and hydrogen present after the big bang. Because these particles had mass, gravitational attraction caused it to 'clump' together. These 'clumps' went on to be the basis of the stars, galaxies, clusters and superclusters.
The evidence for the fluctuations in the universe can be shown by the minute 'ripples' in the cosmic microwave background radiation detected by the COBE satellite.

If you're doing OCR i don't think we need to know the exact dates, just the order in which stuff ocurred and a basic understanding why. My notes have been made straight from the textbook, but theres still probly some mistakes! hope it helps!
Oh my god the exam is tomoro morning! NOOOOOO
16. oh my god you are a star!!
cosmology exam is in the afternoon isnt it??! please tell me its in hte afternoon
17. (Original post by misty)
oh my god you are a star!!
cosmology exam is in the afternoon isnt it??! please tell me its in hte afternoon
no, no im pretty sure its the morning. it will be on the OCR website. Tell you what it better be in the morning i dont think i can cope any longer!
18. im sure its the afternoon.. lol imtalking bout ocr A cosmo option... :s
19. does it matter if you talk abot time dilation in terms of two trains moving away from each other at constant speeds as opposed to one stationary observer... actually the stationary observer is the one in the trrain who emits the light so its the same thing really isnt it?
20. (Original post by misty)
does it matter if you talk abot time dilation in terms of two trains moving away from each other at constant speeds as opposed to one stationary observer... actually the stationary observer is the one in the trrain who emits the light so its the same thing really isnt it?
Stationary to who? That person is certainly not stationary in the light's rest frame, nor the other train's rest frame - only in his/her own.

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