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I'm well aware of the celestial bodies considered as the oldest visible in our galaxy.

My question might feel a bit odd: What is the oldest thing in the universe? I am puzzled with this question as the only answer that I have found by myself sounds weird.

As the notion of "old" only makes sense in an observable and ellapsing timeline, the most obvious answer to me would be "Time is the oldest thing". There is no such thing as a measurement of "old" until there is actually mass to allow time, so which predates which? I'm pretty sure the answer will tightly be linked to Planck's constant, but how?

What am I doing wrong? How could I find relief in an answer that wouldn't be just philosophical, but also logical? :)

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  • $\begingroup$ We don't know anything about the Planck epoch so there might not be a precise answer. Wikipedia has a pretty good chronology page that indicates some of the oldest things. en.wikipedia.org/wiki/Chronology_of_the_universe Gravity is up there. The 3 unified forces were also early (all 4 being unified is still theoretical). We don't know exactly what happens to quarks at those temperatures, so I wouldn't say quarks. For stable matter, probably Electrons. What answer did you come up with? $\endgroup$
    – userLTK
    Commented Oct 12, 2016 at 13:41
  • $\begingroup$ @userLTK I came up with "Time" as my best answer. How could there be gravity without mass, and mass without time? How could there be quarks and / or electrons without matter, and again mass, and therefore time? $\endgroup$
    – Doodloo
    Commented Oct 12, 2016 at 13:50
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    $\begingroup$ If time is a valid answer, you might as well say the Universe. Time is merely one dimension of the Universe. At singularity (assuming there was such a thing and that speaking of it is meaningful at all) there is no dimension, but immediately after both space and time would exist, so why single out time? Space-time has been existing as long as we know. $\endgroup$
    – called2voyage ♦
    Commented Oct 12, 2016 at 14:15
  • $\begingroup$ this "physics-philosophy" question would be for the Physics site, if anywhere. $\endgroup$
    – Fattie
    Commented Oct 12, 2016 at 14:50
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    $\begingroup$ @JoeBlow I strongly disagree with dumping vague questions on Physics, but I do think this question needs some refining. I think the OP is trying to work toward something meaningful however, so I don't think the post is beyond hope yet. $\endgroup$
    – called2voyage ♦
    Commented Oct 12, 2016 at 15:16

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Pretty much every hydrogen atom that's in a glass of water has a proton that dates from 1 / 1000000 seconds after the big bang. That's older than the cosmic microwave background, which dates from almost 400,000 years later.

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  • $\begingroup$ If only protons could talk... $\endgroup$
    – uhoh
    Commented Jan 26, 2019 at 0:32
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If we could detect the cosmic neutrino background, then I would class those neutrinos as "things" and there should be lots of them! I guess whether they are detected or not, they are extremely likely to be there.

These cosmic background neutrinos were produced when the universe was about 1 second old.

I agree that most protons are almost a second older!

But a tiny fraction of a second older than this would be gravitational waves produced at the end of the inflationary epoch (if we can detect them).

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  • $\begingroup$ Interesting. Enjoying that answer as well. $\endgroup$
    – Doodloo
    Commented Oct 13, 2016 at 2:51
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If "time" is considered to be a valid answer, I would like to propose a more fundamental principle: the wave function.

Since a wave function is a description of the quantum state of any physical system, there must necessarily have been a wave function as soon as quantum physics applied to the Universe. Since we generally assume uniformity in nature, there is no reason to consider any sort of "pre-quantum" era.

All right, I can hear some of you complaining already that it says right in the paragraph above that a wave function is a description, but isn't that what time is after all? It is just a description of a change in the state of the Universe. If you really want to split hairs, you can say it's actually a quantum state--but wait that's just a condition of a quantum system--but wait that's just saying that the first thing is a thing. What is a thing, really?

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  • $\begingroup$ And yes, I know that the wave function is time-dependent, but you have to have something to happen when time occurs before you can have time. $\endgroup$
    – called2voyage ♦
    Commented Oct 12, 2016 at 20:36
  • $\begingroup$ I'm enjoying those answer a lot. $\endgroup$
    – Doodloo
    Commented Oct 13, 2016 at 2:49

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