Geodad478 OP t1_j1dg6cn wrote
Reply to comment by a4mula in Can we truly know the age of the universe? by Geodad478
Microwave radiation is still light though. At some point, the CMB radiation would not be visible due to the distance being to far for the light to ever reach us.
The CMB could be extending beyond what we could observe due to the speed of light.
a4mula t1_j1di7zx wrote
This is a challenging and subtle thing, right?
Let's look at it through analogy.
If we have a special kind of dough. One that that continues to grow after we bake it.
And we make a cake. The second that cake comes out of the oven, we put a layer of frosting across the top.
As time goes by, our special kind of dough grows. It makes the cake larger. But it never adds to the amount of icing we put on it. The icing is just stretched in ways so that it remains in the correct proportions.
We can measure that icing, and how it's stretched to determine how much time has passed since we applied it.
That's all this is.
RazeTheIV t1_j1dizhh wrote
This was a fascinating read, thank you and OP. Great question.
hreflet t1_j1dn8vm wrote
First off, I'm not very knowledgeable on the topic but always have trouble understanding how we can confirm things like age of the universe etc.. so forgive me if I'm asking stupid questions.
Your analogy is the first time I've been able to somewhat understand so thanks for that but to follow up, how can we know how much of this "icing" was there to start with in order to accurately tell the age? (Is the icing the cosmic radiation?)
Follow up question. Why do we confrm and deny things based on our limited knowledge? Who's to say that things don't work differently out there in the distant universe? I have trouble thinking that the far universe and even other planets work according to the same laws as we know.
a4mula t1_j1doh37 wrote
There are many different properties of the CMB. Temperature, intensity, spectrum. As time progresses these will all change. From there it's a matter of rewinding the clock back to its original, highest energy state.
We don't know. And the truth is, we can never know with absolute certainty. Science isn't a study of Truth, not really. It's a study of observable phenomena that we use to make models to help us accurately understand our reality.
From that stance, they've been very successful as it gives us technology. Regardless of any Truth statement.
We approach infinity, We approach Truth. Never is either reached.
hreflet t1_j1drti3 wrote
I understand what you're saying.
I just wish I could be alive when we can explore further into the unkown. Any knowledge on this topic fascinates me so much. Thank you again for that icing on the cake analogy. May you have a wonderful day.
a4mula t1_j1dsqm6 wrote
You are alive for that! Look around. So much is being discovered today that nobody can keep up with it all. That's mind blowing to me.
Even as a child in the 80s, I might go months without having some major discovery made, maybe years.
Today I can't get through a single news cycle.
Never fear that we'll run out of discovery. That's not possible. Novel information is created faster than it's absorbed, at least by any given individual.
We're delving into reality in ways today that are mind blowing on many different scales.
The real fear, is running out of time to explore.
shassis t1_j1doje1 wrote
What we “know” is what best fits what we observe. As observations improve then we we know becomes more refined. It appears that the sun revolves around the earth but as instruments and observations progressed we gained a different understanding. It takes time.
ishpatoon1982 t1_j1dpzzj wrote
As for your second question, confirming and denying things based on our knowledge is what science is. If we find new workable theories and/or facts that go against our current process, well...we change our process to fit the newly found evidence.
We work with our knowledge because it's all that we have. We don't have access to anything else besides how we as humans think and retain.
a4mula t1_j1dgkz8 wrote
Sure, but you're confusing the relationship. The age of the universe is determined by the observed properties of the CMB radiation and the expansion rate of the universe, rather than the size of the observable universe or the distance to the CMB radiation.
Geodad478 OP t1_j1difnb wrote
This is why I asked the question here. 🙂
[deleted] t1_j1do7kf wrote
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nicuramar t1_j1ds7we wrote
> The universe is not expanding faster than c. In the very early universe, this was true,
What’s that supposed to mean? Expansion is a rate, not a velocity. Relative velocity is only locally well-defined.
How did the early universe expand at more than c in any way that doesn’t just as well apply now, over enough distance?
drosse1meyer t1_j1e13q0 wrote
Well, if you want to be pedantic, velocity is a rate too, is it not? Distance over time.
Anyway, there are countless articles / studies about this that can explain it far better than anyone on this thread. Suffice it to say, the size of the universe expanded from the planck length to a factor on the order of 10^28 in an extremely short amount of time
Existing radiation would simply be stretched and omnipresent given this massive change. That is why we have the CMB.
nicuramar t1_j1e7dhd wrote
> Well, if you want to be pedantic, velocity is a rate too, is it not?
Yes, but expansion is velocity over distance, so it’s not units of velocity and thus isn’t c or below or above c.
> Suffice it to say, the size of the universe expanded from the planck length to a factor on the order of 1028 in an extremely short amount of time
The observable universe. Maybe, yes, but that doesn’t make it expand at a certain velocity unless you measure over a certain distance. And at this distance, relative velocity wouldn’t be well defined due to the curvature of spacetime, and wouldn’t be constrained to c anyway.
See first answer to this: https://physics.stackexchange.com/questions/400457/what-does-general-relativity-say-about-the-relative-velocities-of-objects-that-a
tr14l t1_j1dp6eg wrote
Some observations: the masses of celestial objects are all moving away from each other, as if expanding. If they are moving away from each other, it's a pretty good assumption that, if we were to rewind that, at one point, they were all together.
Measuring the velocity with which they are moving is easy enough. So, coming up with a model for rewinding that (and how long that would take) is actually not the most complicated thing in the world. If we were to "rewind" it, it would take ~14 billion years. Of course, there may be some variables that effect that age, but most of the biggest ones (gravity, expansion, etc) are fairly easily observed and accounted for. So it is unlikely based off current observations that we are trillions of years off. Millions perhaps, but that's fairly small.
Indigo816 t1_j1dpbbh wrote
Look up physics girl on YouTube. She’s got a video on that.
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