Accelerating Universe

[Kizzi]

I was wondering........

 

As you look further into space one looks back further in time.

So, one would need to take into account the time factor when working out whether the Universe is decelerating, constant, or accelerating?

 

The universe could be decelerating but appear to be accelerating if one does not take into account that further away objects are further back in time.

 

;) Kizzi

 

I suppose I'm asking "Did they take into account that further objects are further back in time when Hubble was working out that the universe expansion is accelerating?"

[Tormod]

Not sure if I understand the question - who were "they"? You mention Hubble.

 

Edwin Hubble observed that the universe is expanding. The *accelerating* expansion was only discovered a few years ago.

[Kizzi]

I was wondering........

 

"Did the scientists who worked out that the expansion of the universe is accelerating take into account that more distant objects are further back in time?"

 

I guess it's a stupid question! They must have.....They're scientists after all.

 

I'll try and be more specific with my questions in future.

;)

[Tormod]

"Did the scientists who worked out that the expansion of the universe is accelerating take into account that more distant objects are further back in time?"

 

Yes. This is well known and would not have been overlooked by cosmologists.

[Aki]

Don't worry Kizzi, there are no such thing as a stupid question:)

[karlfreak]

Don't worry Kizzi, there are no such thing as a stupid question:)

 

yesa there are and i am the one that normally makes them

 

we can see the past cool

[infamous]

yesa there are and i am the one that normally makes them

 

we can see the past cool

 

Yes, thats the most intelligent response I've heard you make to date.

[EWright]

we can see the past cool

 

:) No we can't, we can only see the light eminating from it. :(

[karlfreak]

:( No we can't, we can only see the light eminating from it. :)

 

ruin my fun :(

 

ok so u can not see the exact objects, could one not phraps guess what is happining by the way the light would become broken by phraps something goin in front of the source

[EWright]

could one not phraps guess what is happining by the way the light would become broken by phraps something goin in front of the source

 

:) Huh? :(

[karlfreak]

u know like a shadow type thing

[Bobby]

I was wondering........

 

As you look further into space one looks back further in time.

So, one would need to take into account the time factor when working out whether the Universe is decelerating, constant, or accelerating?

 

The universe could be decelerating but appear to be accelerating if one does not take into account that further away objects are further back in time.

 

:shrug: Kizzi

 

I suppose I'm asking "Did they take into account that further objects are further back in time when Hubble was working out that the universe expansion is accelerating?"

 

 

 

From General Relativity ===> T1 = T2 ( 1 + gh/c^2). Essentially, this equation says that the further you get from a source of gravity, the slower time runs. To generalize, let us say that clocks run slow in a gravitational field and let us specify that clocks measure some undefined "something" we call time.

 

During the early periods of the Universe gravity must have been tremendously strong and clocks would have run at an exceedingly slow rate. As the Universe expanded, gravity at any particular point would have grown weaker and clocks would have begun to speed up.

If the expansion continues, gravity will continue to become weaker and clocks will continue to run faster.

 

As you say, when looking out in space you are also looking back in time. If time ran slower in the past, this would look to us as if the rate of expansion is acellerating.

 

This said, now we get into the flaky stuff. What does it mean to say that clocks run fast? Fast is a relative term. If you used a clock to measure time early in the big bang and use the same clock to measure time today, you would get the same answer.

[Kizzi]

1)....... Essentially, this equation says that the further you get from a source of gravity, the slower time runs.

 

2)....... If the expansion continues, gravity will continue to become weaker and clocks will continue to run faster.

 

3)....... If the expansion continues, gravity will continue to become weaker and clocks will continue to run faster.

 

4)....... If you used a clock to measure time early in the big bang and use the same clock to measure time today, you would get the same answer.

 

 

1) and 2) seem to contradict each other.

 

3) and 4) seem to contradict each other.

 

Kizzi :shrug:

 

ps. Maybe I'm mixed up.

[Bobby]

1) and 2) seem to contradict each other.

 

3) and 4) seem to contradict each other.

 

Kizzi :shrug:

 

ps. Maybe I'm mixed up.

 

 

 

OOps. T1 = T2 (1 + gh/C^2) would mean clocks run FASTER not slower.

 

 

Re 3 and 4, consider again that T1 = T2 (1 + gh/C^2). This means a clock on the surface of the Earth would run slower than a clock on the moon. However, it is all relative. If you were on the Moon, the Earth clock would be seen as running slow while someone on the Earth would see the moon clock as running fast.

 

Cosmologists use various physical means to determine Cosmic distances and times. One of those is a particular type of star. Suppose that star is know to flash a certain number of times depending on its brightness. Suppose also that you know the distance to some particular star of that type to be 100 Light Years away. If you then find another star of the same type and its brightness is only 1/2 the brightness of the know star, you could determine the distance to the new star.

 

However, just as a clock on the moon would be seen as running fast by an observer on the Earth, both of these stars would have their own particular clock rates. If the star in question is in a more intense gravitational field, then its clock as seen from earth would run slower than the clock at the know star.

[Kizzi]

Does the equation above mean :-

 

The higher the gravity the slower the clock speed.

 

So, as there's more gravity on earth compared to the moon, a clock will run slower on Earth, and hence a clock will run faster on the moon.

 

Kizzi :shrug:

[Bobby]

Does the equation above mean :- The higher the gravity the slower the clock speed

 

Essentially, yes. The g is the acelleration due to gravity (as in 32 fet/sec^2), h is the distance away from g (the surface of the earth) and c is the speed of light.

 

 

 

So, as there's more gravity on earth compared to the moon, a clock will run slower on Earth, and hence a clock will run faster on the moon.

 

 

Yes. This was one of the major tests of the manned lunar landings.

[Kizzi]

So time runs slower on surface of Earth than on surface of Moon.

 

Now, if there was a human on the Moon with a powerful telescope pointed at a perfect clock on the Earth, and there was also a human on the Earth with a powerful telescope pointed at a perfect clock on the moon. Now, assuming both the Moon and the Earth are stationary would the man on the Moon think the clock on Earth is running slow compared to his clock on the Moon, and would the human on Earth think the clock on the Moon is running fast compared to the clock on Earth?

 

The answer must be yes i guess.

 

Kizzi :shrug: