Relative model of the universe

[michel123456]

Question:

If the model of the universe is based on Relativity, doesn't it follow that the model is relative?

IOW that the Big Bang and expansion is a relative observation and not an absolute model: that any observer in the universe, be it today here or there or 10 billion years in the future and the past, will observe the universe having an age of 13.799±0.021 billion years?

[Strange]

Question:

If the model of the universe is based on Relativity, doesn't it follow that the model is relative?

IOW that the Big Bang and expansion is a relative observation and not an absolute model: that any observer in the universe, be it today here or there or 10 billion years in the future and the past, will observe the universe having an age of 13.799±0.021 billion years?

 

Why would you think that? A fundamental part of the model is that the universe is expanding and cooling. So observers in future will see a cooler universe (a more greatly red-shifted CMB) and therefore a different age.

[michel123456]

I would think that because the Theory on which the model is based is called Relativity.

[Klaynos]

It's a result of the assumption that Maxwell's equations work everywhere.

[Strange]

I would think that because the Theory on which the model is based is called Relativity.

 

So you are extrapolating from the name rather than looking at what the theory says.

[michel123456]

 

So you are extrapolating from the name rather than looking at what the theory says.

The theory says about what a random observer observes.

[Strange]

The theory says about what a random observer observes.

 

Yes, but what does it say? The big bang model says that the universe is expanding and cooling. Therefore people at different times will see a temperature with different density/temperature.

[michel123456]

At least you agree that the BB model is based on Relativity.

 

The first question is what Relativity says.

 

Yes, but what does it say? The big bang model says that the universe is expanding and cooling. Therefore people at different times will see a temperature with different density/temperature.

The BB model should say that a random observer observes a universe that is expanding and cooling.

And I think the BB model actually says that.

The second part of your statement is not a direct implication of the first (mine).

Edited February 7, 2016 by michel123456

[Strange]

At least you agree that the BB model is based on Relativity.

 

Of course.

 

 

The first question is what Relativity says.

 

It says that the universe is expanding and cooling. Therefore people at different times will see a temperature with different density/temperature.

[michel123456]

 

Of course.

 

 

It says that the universe is expanding and cooling. Therefore people at different times will see a temperature with different density/temperature.

Cross posting.

The BB model should say that a random observer observes a universe that is expanding and cooling.

And I think the BB model actually says that.

The second part of your statement is not a direct implication of the first (mine).

[Strange]

Cross posting.

The BB model should say that a random observer observes a universe that is expanding and cooling.

And I think the BB model actually says that.

The second part of your statement is not a direct implication of the first (mine).

 

Huh? If the universe is cooler now than it was in the past, how can we not see a cooler universe than past observers?

You seem to be saying that the universe has always been the same. That is contradicted by the evidence.

[uncool]

In relativity, not everything is relative. Certain things are not, and can be quantified invariantly. The typical example of this is the metric between two "events" - that is, points in space-time.

 

As such, if we can describe a path from the Big Bang to now, we'd be able to define a "proper time" for that path - and so a "proper age" for the universe. That age would be path-dependent, but it would be invariant - that is, it would be independent of the choice of observer.

[michel123456]

Evidence is observation, and observation is ruled by Relativity.

 

I say that Relativity teaches that things are relative. IOW that we are observing a universe that cooling, that we are measuring a universe that is cooling. And that Relativity says that any random observer must observes that.

In relativity, not everything is relative. Certain things are not, and can be quantified invariantly. The typical example of this is the metric between two "events" - that is, points in space-time.

 

As such, if we can describe a path from the Big Bang to now, we'd be able to define a "proper time" for that path - and so a "proper age" for the universe. That age would be path-dependent, but it would be invariant - that is, it would be independent of the choice of observer.

That is for another thread: to be invariant is perfectly compatible with relative, invariant does not necessarily mean not-relative (absolute)

Edited February 7, 2016 by michel123456

[swansont]

Evidence is observation, and observation is ruled by Relativity.

 

I say that Relativity teaches that things are relative. IOW that we are observing a universe that cooling, that we are measuring a universe that is cooling. And that Relativity says that any random observer must observes that.

Yes. So what's the question? Is it whether two observers would come up with the same age? It depends on whether they had adjusted their clocks to compensate for their frame of reference.

[Strange]

I say that Relativity teaches that things are relative. IOW that we are observing a universe that cooling, that we are measuring a universe that is cooling. And that Relativity says that any random observer must observes that.

 

Yes, observers at all times will observe a universe that is cooling. That is why they will see a different temperature (and therefore age) than people at different times.

[michel123456]

Yes. So what's the question? Is it whether two observers would come up with the same age? It depends on whether they had adjusted their clocks to compensate for their frame of reference.

Yes.

The question can be summed up like you are stating.

It is whether 2 observers at different places (and at different time frames) would observe the same thing.

 

Both observers use Relativity and measure the same thing, they will conclude the same thing: the universe is 13.799±0.021 billion years.

 

Or the above is wrong and it goes like this:

both observers at different places (and at different time frames) use Relativity and measure different things and thus conclude that the universe has a different age.

[Strange]

If someone in a billion years makes observations, they will get different results and conclude that (at that time) the universe is 14.8 billion years old. Someone 1 billion years ago would have got different results and calculated that the universe is 12.8 billion years old.

 

At different places (at the same time) the differences would probably be too small to measure, but they would lead people to conclude the same age for the universe.

Edited February 8, 2016 by Strange

[swansont]

Yes.

The question can be summed up like you are stating.

It is whether 2 observers at different places (and at different time frames) would observe the same thing.

 

Both observers use Relativity and measure the same thing, they will conclude the same thing: the universe is 13.799±0.021 billion years.

 

Or the above is wrong and it goes like this:

both observers at different places (and at different time frames) use Relativity and measure different things and thus conclude that the universe has a different age.

"Measure the same thing" is ambiguous, but basically both are wrong. We define our time based on a standard at the surface of the earth. We don't normalize this to a measurement in deep space. If someone defined a standard in a different potential well, they would get a different answer for the time. Their second would not be the same as ours.

[David Levy]

If someone in a billion years makes observations, they will get different results and conclude that (at that time) the universe is 14.8 billion years old. Someone 1 billion years ago would have got different results and calculated that the universe is 12.8 billion years old.

 

At different places (at the same time) the differences would probably be too small to measure, but they would lead people to conclude the same age for the universe.

 

Is there any possibility for us to verify - even a minor change, in our life time?

Edited February 8, 2016 by David Levy

[swansont]

Is there any possibility[/size] for us to verify - even a minor change, in our life time?

Unless they were in an appreciably different potential well, no.

[Strange]

 

Is there any possibility for us to verify - even a minor change, in our life time?

 

Look at the error bars. Even if you waited 20 million years you wouldn't be able to tell the difference.

[michel123456]

If someone in a billion years makes observations, they will get different results and conclude that (at that time) the universe is 14.8 billion years old. Someone 1 billion years ago would have got different results and calculated that the universe is 12.8 billion years old.

 

At different places (at the same time) the differences would probably be too small to measure, but they would lead people to conclude the same age for the universe.

why?

[Strange]

why?

 

Why what?

 

Let's try a (not unrealistic) analogy. Imagine someone finds a dead body. They check the temperature and determine from how much it has cooled that the murder took place 2 hours ago. They call the pathologist / medical examiner who arrives 2 hours later and checks the (now lower) temperature and determines that the murder too place 4 hours ago.

 

Is that unreasonable? If so, why?

[michel123456]

 

Why what?

 

Let's try a (not unrealistic) analogy. Imagine someone finds a dead body. They check the temperature and determine from how much it has cooled that the murder took place 2 hours ago. They call the pathologist / medical examiner who arrives 2 hours later and checks the (now lower) temperature and determines that the murder too place 4 hours ago.

 

Is that unreasonable? If so, why?

How do we measure the temperature of the universe?

[Strange]

How do we measure the temperature of the universe?

 

The CMB has a black body spectrum and therefore an associated temperature. (Or, to put it another way, it is thermal radiation and therefore has a black body spectrum.)