B Is the Universe older than we think?

[PeterDonis]

You are all talking about measurements, which I agree cannot be made.

Nobody else but you has said that measurements cannot be made.

I am asking from a theoretical point of view.

The theory is tested by making measurements and comparing the theory's predictions. It makes no sense to say "well, there is no way to ever make this measurement, but what does the theory say about it?"

 

[Tanelorn]

Peter, I am a very old engineer who faces real life practical problems every day. Putting a spaceship in orbit close to a BH is about as speculative to me as... It will never happen.
That said the Parker solar probe is doing something vaguely similar.

So no more thought experiments aye?

 

[Ibix]

Putting a spaceship in orbit close to a BH is about as speculative to me as... I doubt it will ever happen.

But the only real problem is that we don't have a black hole to hand. If we had one it would be no more difficult than any other space probe to Jupiter or whatever.

The problem with "did time run faster in the early universe" is that we can never have the early universe and the current universe side-by-side to compare clocks.

One is a purely practical problem. The other is trying to sneak around causality somehow.

 

[Tanelorn]

So therefore, in both cases, we have to rely on theory and common sense, because neither experiment is going to happen. Anyway, I am happy with Peter's answer regarding no local gravitational potential.

 

[PeterDonis]

I am a very old engineer who faces real life practical problems every day.

That's fine. But physics is not engineering.

Putting a spaceship in orbit close to a BH is about as speculative to me as... It will never happen.

But it is still permitted by the laws of physics. Exchanging light signals with a hypothetical atomic clock at the surface of last scattering is not.

no more thought experiments aye?

Thought experiments are a useful tool in physics. But you do not appear to understand how thought experiments work. They work by setting up a scenario that, however unlikely in practice, is permitted by the laws of physics.

 

[Tanelorn]

"But it is still permitted by the laws of physics. Exchanging light signals with a hypothetical atomic clock at the surface of last scattering is not."

You mean because it would need us to be able to go back in time to put the clock there?
A minor inconvenience for a theoretical approach or thought experiment, as I understand the meaning anyway.

Thanks all, I have to take care of other matters now.

 

[Ibix]

So therefore, in both cases, we have to rely on theory and common sense, because neither experiment is going to happen.

What is the heaviest weight I can lift?

What is the heaviest weight Superman can lift?

We can come up with a way to predict tha answer to the first question with "theory and common sense" and a bit of data about me even if I am never directly experimented on. The second one founders on the fact that Superman isn't real so there are (and can be) no numbers to put in to whatever model you use to calculate my score.

Similarly, you have no way to compare clocks in the early universe to clocks today. So there is nothing to put into the theoretical model. It's not just "we haven't done it and it would be really hard", it's "there is nothing you could do even in principle to compare clocks".

Because it would need us to be able to go back in time to put it there?

No, there are plenty of periodic sources in the early universe that can serve as clocks. The problem is you have no way to compare what a modern clock is doing to what an ancient one is doing. We can only look at the past clock, the past clock cannot look at us.

 

[Tanelorn]

So, to be able to confirm any time dilation effect you also need the past clock to be able to look at our clock today. I didn't realize that this would be necessary to confirm any time dilation effect. Ok well I am not going to disagree (for now) except to say that it could have been said with less messages.

 

[Vanadium 50]

except to say that it could have been said with less messages.

Because one of our number refused to accept that.

 

[PeterDonis]

You mean because it would need us to be able to go back in time to put the clock there?

No, because even if you assume that there was such a clock back then, which in a thought experiment you can assume since it does not violate the laws of physics, you still would not be able to exchange light signals with it, because that does violate the laws of physics.

I didn't realize that this would be necessary to confirm any time dilation effect.

Even after you had been told that multiple times, apparently.

I am not going to disagree (for now)

If you end up disagreeing later you will earn yourself a warning.

except to say that it could have been said with less messages

It could have, if you had paid attention to any of them:

How would you even compare a clock now to a clock in the past? There's a concrete meaning to "which clock is faster" in the black hole case because each clock can watch the other and send signals to the other. There's no such meaning to comparing one clock now to one clock in the past - only one can watch the other and only one can signal the other.

How are you going to compare the tick rates of two clocks that are billions of years apart? If you can't come up with such an experiment then your question isn't well-posed enough to answer.

I repeat again: how could you compare the rates of two clocks billions of years apart?

How are your clocks in the past and the present even in theory going to exchange light signals? This is the question you seem to be just hoping will go away if you repeat "theoretical" often enough. It won't. You still need an experimental setup to describe in the model. If you don't, you have nothing to describe with the theoretical model.

The problem with "did time run faster in the early universe" is that we can never have the early universe and the current universe side-by-side to compare clocks.

By my count that's five previous messages just from @Ibix alone that you didn't pay attention to.

 

[PeterDonis]

The OP question has been answered and the sidebar has gone on long enough. Thread closed.