Now this makes no sense

pants on fire

I was out for a walk 1 night, and i had a thought.
Every1 knows about the Doppler effect, and the way the frequency of the noise apparantely increases if the source is moving towards the observer. The sound waves are closer together..........etc.
I was looking into the nights sky, and started thinkin:
If there was a planet identical to Earth 3 million light years away, and the light from it reached Earth 1 million years ago (just for arguments sake!!), we'd now be seeing what was happening on that planet 1 million years into its life.
However if we were to move towards that planet at half the speed of light, for example, we would be seeing what was happening on the planet at 1 and half times the speed it actually happened...kinda like 'fast forward'!
Does that mean that as i walk towards some1 on the street, I am actually experiencing this same effect on a very small scale?
This is wreckin my head!!

rugbug86

in theory, yes. but you are moving forward towards them and if you were being "pulled" to another planet you would be moving up to the planet...

just my 2 ha'pennies

*shrug*

pants on fire

that makes no sense.

Amz

pants on fire wrote:

that makes no sense.

That's what I was thinkin'.

Sangre

No because the Doppler effect only alters the frequency of the wave not the speed. So higher frequency when approaching means higher pitch and vice-versa.
What happens on the galatic scale is the frequency change alters the colour of light and causes the red or blue effect, depending on whether a galatic body is approaching or receding.
Its a useful technique for measuring the expansion of the universe.

Sangre

Also with the universe expanding I don't think 2 planets in orbit around a star could approach each other.

Capt'n Midnight

Sangre wrote:

Also with the universe expanding I don't think 2 planets in orbit around a star could approach each other.

hang on to your hat our galaxy will "collide" with andromonada in a few bilion years...

Sangre

Would you mind telling me why/how? How can they be moving towards each or the same point. Wouldn't each of those scenarios require a different universal starting point or is to the with the orbit of out solar system in a galaxy or some such?
Similarily won't gravitonal effects be the first thing to worry about before we 'collide' with it?

I have no science background I'm just saying what seems logical.

Capt'n Midnight

http://www.nasa.gov/audience/forstudents/5-8/features/F_When_Gallaxies_Collide.html

Light moves at 300,000,000Km/Second so you would have to travel very fast to notice a change in visible light by walking down the street. GPS clocks have to run at a corrected speed though because they do move fast enough for relativity to affect them.

Zillah

Capt'n Midnight wrote:

http://www.nasa.gov/audience/forstudents/5-8/features/F_When_Gallaxies_Collide.html

Light moves at 300,000,000Km/Second so you would have to travel very fast to notice a change in visible light by walking down the street. GPS clocks have to run at a corrected speed though because they do move fast enough for relativity to affect them.

What...the hell...?


I suspect he was talking about the speed of movement of the planets as opposed to his speed walking down the street...

And Sangre is quite right, compression of the light wave like that alters its colour towards red or blue depending on if its heading towards or away.

pants on fire

Ref the thread called 'Help!'

I posted that thread last Fri, but made a fatal error i just realised.
First of all, 'Sangre', as events happen, light waves are emitted in real time. Imagine if you moved towards them at half the speed they were moving towards you. The light waves being emitted would appear closer together relative to the observer. Therefore, it should seem as if the events were happening faster than they actually were.
This would have to make sense, because if I was to travel from here to a planet 3 million light years away, I would have to witness everything that happened on that planet (assuming i can see whats happening even at a distance of 3 million light years) between the time i left Earth and the time i arrived at the planet. Since I am moving at a speed faster than the speed of light (relative to the actual light waves i am observing), events are going to unfold faster than they actually did. That would have to make sense.
HOWEVER!!!
Most of you will have spotted that Einsteins Special Relativity will not allow ANYTHING to move at a speed faster than light. In theory, if I am moving half the speed of light, and i pass light travelling in the opposite direction, relative to me, the light will still only be moving at the speed of light.
Doesn't this mean that if was moving towards this planet at half the speed of light, I am not going to witness events taking place faster than they did. I will see everything on the destination planet occur at the same pace they actually did occur.
So going with this, I leave earth at half the speed of light, my destination being this planet 3 million light years away.(I'll call this Path 1) Although I observe all ocurrences on the destination planet at the pace they actually ocurred, i am actually moving at 1 and a half times the speed of light, and therefore should be observing these occurrences at 1 and a half times the pace they occurred.
Like i said this isn't the case due to Special relativity. Think about it this way...If i was to witness events occuring at 1 and a half times the pace they occured, by the time i come to a stop at the destination planet, everything would have just caught up with me and i would have just experienced a complete history of the planet happening at a speed proportional to the speed I had just travelled at. (as long as my speed was greater than the speed of light, theoretically relative to the observer).
But Einstein tells me that as I move, the events happen at the pace they actually happened. So therefore, when I stop at the destination planet, I would go from seeing what happened at two thirds way through Path 1, to immediately seeing what was happening in real time. The latter One third of its history would just not be witnessed at all by the observer.

GuanYin

No need for two threads.

Merged.

acri

i think this may have been asked, but how can two galaxies move toward each other? if we are to believe in the theory of the big bang, all bodies are moving out, away from each other. eventually the massive vacuum in the centre of all this will pull all bodies together creating the big crunch, and it starts all over again. aparently this is relentless, but i cant grasp the concept of infinity so i dunno what to believe.

Sangre

Oh I see what you're trying to say, unfortunately this way past my knowledge of the subject.

Ok, travelling at half the speed of light towards a planet 3mil light years away.
Any light we see is 3mill years old from their planet.
We travel to their planet in 6 mill years, however 9mil years of history has passed before our eyes.....*ow* my head hurts aswell.

Of course that is assuming the other planet is stationary...or something.

aku0000

Although the inital force of the big bang is pushing everything outward. gravity still applys. both gravity and spacial drift apply. think of it like throwing a load of magnets accross a room. some may click together in mid air. but they will not stop moving away from you (untill they hit the ground).
also because most stuff is near the center of the universe gravity is pulling in. pulling against spacail drift. after a while things stop. when start moving in. as more stuff gets closer to the center gravity becomes grater. when everything reaches the center the gravity is so emense that everything is pulled into a single point - this is the big crunch. it has nothing to do with vacumes in the center.

(sorry about the spelling)

acri

whats generating the gravity in the centre?

Capt'n Midnight

Zillah wrote:

I suspect he was talking about the speed of movement of the planets as opposed to his speed walking down the street...

Even if you look at the planets in the solar system moving then the doppler shift wouldn't be readily visible to the naked eye, but it would be very easy to measure since we have good measuring gear.

pants on fire wrote:

Does that mean that as i walk towards some1 on the street, I am actually experiencing this same effect on a very small scale?

Sound travels 1000,000 times slower than light and it's effect is heard every day in the changing tones of passing cars.

acri wrote:

whats generating the gravity in the centre?

Gravitions ? If you accept that matter distorts space time then you don't need something to generate gravity. More matter just distorts it more and since gravitational attraction depends on the product of the mass's then the effect gets stronger as matter concentrates. BUT there are many stable orbits even when an object has been captured (eg: earth objects can orbit from 88 minutes to over a month when out side the moons orbit) so unlike magnets you don't always end up them all together. "the stars in the galaxy are so far apart that it would be like haveing 3 bees flying over Europe" - not too sure how accurate that is but even in the projected merging of our galaxy and andromenda most start won't collide they will pass by.

acri

so you're saying dark matter fills the centre of the universe? or the known universe rather. or is it the assumed universe?

aku0000

the magnets were ment to just show that somthing doesn't nead to stop traveling outward to collide just turn a little. never mind it is a silly analagy.

causal

pants on fire wrote:

Does that mean that as i walk towards some1 on the street, I am actually experiencing this same effect on a very small scale?

Yes
And the faster you approach them the quicker you'll meet

It might be easier to think of looking at a clock - if you moved away from the clock at the speed of light - then the light reflected/emitted from the clock would never reach your eye - hence it would appear motionless. Of course it's still ticking/vibrating away - you just haven't observed it.

Conversely, if you were to move toward the clock at the speed of light then you'd probably break your nose

causal

ISAW

pants on fire wrote:

Ref the thread called 'Help!'

[snip]

HOWEVER!!!
Most of you will have spotted that Einsteins Special Relativity will not allow ANYTHING to move at a speed faster than light. In theory, if I am moving half the speed of light, and i pass light travelling in the opposite direction, relative to me, the light will still only be moving at the speed of light.
Doesn't this mean that if was moving towards this planet at half the speed of light, I am not going to witness events taking place faster than they did. I will see everything on the destination planet occur at the same pace they actually did occur.
So going with this, I leave earth at half the speed of light, my destination being this planet 3 million light years away.(I'll call this Path 1) Although I observe all ocurrences on the destination planet at the pace they actually ocurred, i am actually moving at 1 and a half times the speed of light, and therefore should be observing these occurrences at 1 and a half times the pace they occurred.
Like i said this isn't the case due to Special relativity. Think about it this way...If i was to witness events occuring at 1 and a half times the pace they occured, by the time i come to a stop at the destination planet, everything would have just caught up with me and i would have just experienced a complete history of the planet happening at a speed proportional to the speed I had just travelled at. (as long as my speed was greater than the speed of light, theoretically relative to the observer).
But Einstein tells me that as I move, the events happen at the pace they actually happened. So therefore, when I stop at the destination planet, I would go from seeing what happened at two thirds way through Path 1, to immediately seeing what was happening in real time. The latter One third of its history would just not be witnessed at all by the observer.

a few observations

Special Relativity as I see it does NOT say nothing can move faster than light as I see it. It suggests no information can be transferred faster than light. Think of a cloud away on the horizon and a light beam sweepting out the cloud. In theory the beam could travel along the cloud faster than light but someone at one end couldnt send a message to someone at the other end faster than light.

But witnessing history IS receiving information. I think the confusion comes from two things. Both have to do with the idea of time, history and observers. By stating that "that event happened three million years ago you are forcing a privelidged frame on the example.


First there are TWO reference frames here. One where the observer A is fixed in a constant distance of three light years observing the moving person B. second is B moving towards a star which before he started was three million light years from A and B. Einstein used Fitzgeralds maths to show that how A dand B perceive time is different. Things that happen at the same time for B do not happen at the same time for A. In essence motion does things to time and similtanuous events are not similtanuous.

To me the idea of "the light from that star left a million years ago so we are looging at something in our history" doesent make any sense since we witness the present AS IT HAPPENS. It woul only make sense if one could be in both places at once i.e one could "jump" to that star. Now that isnt covered by relativity since it is a non local causal effect or as Einstein stated a spooky action at a distance. It does however seem to happen. the Aspect Experiment is one example.

ISAW

Capt'n Midnight wrote:

Even if you look at the planets in the solar system moving then the doppler shift wouldn't be readily visible to the naked eye, but it would be very easy to measure since we have good measuring gear. Sound travels 1000,000 times slower than light and it's effect is heard every day in the changing tones of passing cars.

Indeed, doppler shift is used to measure the rotation of galaxies. If for example we view another galaxy edge on we can see that populations of stars are red shifted on one side and blue shifted on the other. this enables a calculation of the angular momemtum (spin) of the galaxy.

I think Bart Bok was involved in this. anyway they found that the galaxies were not spinning at the right speed so there had to be more matter - hense Dark matter raising its ugly head again.

Actually this "wobble" in the spectrum was the first method uded to detect planets around other stars (if indeed they are planets and not brown dwarfs or suchlike)

http://zebu.uoregon.edu/51peg.html

breadmonkey

On the subjct of stuff moving faster than the speed of light, this is all i know

m = m'/((1-(v^2)/(c^2))^1/2

I know thats's horribly confusing the way it's written above but m is your mass at speed v, m' is your rest mass, and c is the speed of light.

So if v becomes bigger than c (i.e. you are going faster than the speed of light), then you get the square root of a negative number on the bottom, and then you're fúcked...

ISAW

breadmonkey wrote:

On the subjct of stuff moving faster than the speed of light, this is all i know

m = m'/((1-(v^2)/(c^2))^1/2

I know thats's horribly confusing the way it's written above but m is your mass at speed v, m' is your rest mass, and c is the speed of light.

So if v becomes bigger than c (i.e. you are going faster than the speed of light), then you get the square root of a negative number on the bottom, and then you're fúcked...

first even with v=c v squared over c squared = 1 since 1-1 = 0 the bottom bit is the square root of zero. Now how do you divide m' by zero?

And what about Hawking's "imaginary time"?

are the fitzgerald contractions approximations and do the tensors provide greater detail?

Capt'n Midnight

ISAW wrote:

Actually this "wobble" in the spectrum was the first method uded to detect planets around other stars (if indeed they are planets and not brown dwarfs or suchlike)

Let's not forget that Jupiter could be considered a failed star and that the terresterial planets were most likely comprised mostly of gas that was later blown away. Venus used to have an ocean. If a brown dwarf was formed from supernova remnants then is should have heavier atoms and it's outer layers were blown away by solar wind/radiation (escape velocity permitting) you'd end up with a planet sized yoke..

did I see somewhere that they reckoned that a primordial planet flung into space would still be warm enough to support life for a billion(s) of years if it had it's gas layer as insulation ?

ISAW

Capt'n Midnight wrote:

Let's not forget that Jupiter could be considered a failed star and that the terresterial planets were most likely comprised mostly of gas that was later blown away.

Not really jupiter isnt nearly massive enough.

Venus used to have an ocean.

Say you. what evidence is there for this?

If a brown dwarf was formed from supernova remnants then is should have heavier atoms and it's outer layers were blown away by solar wind/radiation (escape velocity permitting) you'd end up with a planet sized yoke..

interesting and it seems plausible. Again any models you can point me to?

did I see somewhere that they reckoned that a primordial planet flung into space would still be warm enough to support life for a billion(s) of years if it had it's gas layer as insulation ?

I dont know did you? I would also like to take a look at that reference. It is quite interesting.