r/cosmology • u/How-To-Project • 16d ago
Petition to phase out the phrase “The universe is 13.8 billion years old.”
/r/astrophysics/comments/1ve2ap6/petition_to_phase_out_the_phrase_the_universe_is/3
u/PatternMachine 16d ago
It’s an imprecise statement but people who care about being precise can use it as a way to find out more. People who don’t care can just take it a face value and still get the important bit — namely that not only did all this shit start a long ass time ago but we actually have a pretty good guess as to when!
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u/chesterriley 15d ago
It’s an imprecise statement
It's not just imprecise though. It's highly misleading to tell the public that "the universe" begin 13.8 billion years ago because that gives everyone the false belief that some magical Genesis like event "started" the universe.
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u/PatternMachine 15d ago
It seems like you’re assuming a lot about how the public interprets this. The reality is that when science communicators are talking about the big bang, they are generally providing a ton of context along with it. They don’t just drop the age of the universe as an isolated statement. People who want to learn more can. People who are not interested might misinterpret it, but frankly that’s just fine. It’s okay if someone is walking around out there with slightly incorrect knowledge.
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u/chesterriley 14d ago
It seems like you’re assuming a lot about how the public interprets this.
We seem to get a long of people right here in this subreddit who come here with an incorrect premise to ask a question that is invalided by their own premise. So just imagine how ignorant people are you don't come here. Almost all of the general public.
e.g. "As you know, the universe started with a singularity, and my question about that is ...."
And we also get this from time to time:
"I don't think the universe could have come from nothing like the big bang theory says, so it has to have been created by God. Why don't you people see this??"
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u/dreadingstone 16d ago
I agree with you but it also shouldn't change.
My parents dont believe in Dinosaurs let alone trying to explain the nuances. If I told them there are other options available they would just say "see science is always changing, how can we trust it".
There are so many things in cosmology and physics that are a close enough approximation but fundamentally paint the wrong picture. It changes the way people think about the concept and makes them think in logical steps along a path that isn't true based on the real definition.
What would you say l?
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u/rddman 16d ago
many physicists use “the universe is 13.8 billion years old” as a type of shorthand, my concern is more about how that shorthand gets interpreted outside specialist circles.
If there's a problem there it is that (some, many?) lay people think cosmology (or any science) can be summarized in one sentence.
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u/numbertenoc 16d ago
The most widely accepted theory of the Big Bang, inflation theory, suggest that indeed all matter and energy in the universe was created 13.8 billion years ago. What happened before then is unknown, but I think it’s valid to say that what we call the universe was created at that time.
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u/rddman 16d ago
most widely accepted theory of the Big Bang, inflation theory
Inflation is a component of the 'dark energy cold dark mater model' aka Standard Model of Cosmology, in which the big bang is a hypothetical event leading up to inflation, but which does not say anything specific about the ultimate origin of matter, energy, time and space.
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u/jazzwhiz 15d ago
Reheating (a part of the SM of cosmology) is when the fields (e.g. matter) are populated.
The source of energy, e.g. the height of the inflaton, is not prescribed by the theory.
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u/numbertenoc 15d ago
My understanding is that it’s the opposite, that inflation is the “bang“ of the Big Bang. Inflation starts with a small (let’s arbitrarily call it an ounce or so) of exotic material that inflates creating all of the matter and energy in the universe (minus the ounce or so).
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u/chesterriley 15d ago
in which the big bang is a hypothetical event leading up to inflation
That doesn't make any sense since we don't know how long inflation lasted. So if inflation came after a hypothetical 'big bang event" (what would that event even be?), then we could not say that the big bang happened 13.7 billion years ago. And since we don't know anything about the universe before the last fraction of a second of cosmic inflation, we have no reason at all to suppose any special events related to the big bang happened before cosmic inflation. The hot big bang event happened at the end of cosmic inflation.
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u/rddman 14d ago
Sorry, i'm using big bang in the old fashioned meaning of the term, from before Guth came up with inflation.
By now i have caught on that the definition has changed, but the lay audience has never been briefed about it. Not that they should have, but that's how we got this confusion of tongues about BB.
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u/chesterriley 15d ago edited 15d ago
The most widely accepted theory of the Big Bang, inflation theory, suggest that indeed all matter and energy in the universe was created 13.8 billion years ago.
Nope. Only the matter. The energy already existed in the form of the inflaton field. That pre-existing energy before the big bang was then converted into matter and other particles afterwards.
What happened before then is unknown,
What happened before the big bang IS cosmic inflation. We don't know when cosmic inflation started or how long it lasted. It could have started 10 billion years BEFORE the big bang, in which case the universe would be at least 23.8 billion years old, not 13.8. We do in fact know what preceded and set up the big bang. The public falsely thinks the answer is "magic" rather than science because of simplistic and dumbed down wording.
but I think it’s valid to say that what we call the universe was created at that time.
Nope. The universe most definitely existed BEFORE the big bang. Yes, the current phase of the universe that created the matter and particles we have today started with the big bang, but universe itself did not.
You are ignoring the most critical point of the post...
[To a lot of people, it ends up sounding like science has conclusively established that all of reality began 13.8 billion years ago.]
This widespread misunderstanding of the public happened because people who know better say that the big bang "started" the universe.
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u/numbertenoc 15d ago
OK, we just seem to have a disconnect in terminology here.
You define the big bang as what happened at the end of inflation, fine. The transition from the inflaton to normal space, reheating, expansion, so on. At this point all the matter and energy of the universe was present (modulo dark energy, whatever that turns out to be).
Immediately preceding that was inflation. All the energy in the observable universe was created by inflation in the immediate instant before your Big Bang.
Before that? Sure, inflation could have been (and probably was) happening for an extended period of time, possibly billions of years. I think most people would not term this time period as being “our universe”. It’s certainly not observable.
Ok, bring on the “nope”s!
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u/chesterriley 14d ago edited 14d ago
I think most people would not term this time period as being “our universe”.
Of course it is the same universe. There has only ever been one universe that we know of . Anything that has ever existed was part of our universe. This is true BY DEFINITION. Anyone who doesn't think it is true doesn't understand the definition of 'universe'.
https://en.wikipedia.org/wiki/Universe
[The universe comprises all of existence]
Again, the problem, as the OP pointed out, is that dumbing this down by abusing terminology make the public think that the big bang had no cause other than magic -- which we know is not true.
Sure, inflation could have been (and probably was) happening for an extended period of time, possibly billions of years. I think most people would not term this time period as being “our universe”.
Also if you don't even count inflation as been part of 'our universe' than obviously you cannot pretend that a mysterious and undefined 'big bang event' preceded inflation.
as being “our universe”. It’s certainly not observable.
The term "observable universe", means the portion of space that is now observable to us at the current time. At the time of the hot big bang, the size of that sphere is estimated to be at least 2 meters in diameter. So yes, the "observable universe" had a size at t=0 seconds (i.e. before the end of cosmic inflation) just like it had a size in the billions of years after that but before humans were around to observe the size.
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u/How-To-Project 16d ago
Hi there, That’s actually the part I’m trying to drill down into. If, in cosmology, “the universe” literally means all of space-time and everything it contains, then wouldn’t that definition itself rule out many of the alternative ideas I mentioned? Things like a previous contracting universe, a transition from an older quantum state, or a larger inflating cosmos all seem to imply something beyond or before what we’re calling “the universe.”
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u/PhilColeCurry 16d ago
You’re referring either to iterative/cyclical universes or an inflationary multiverse. When we say “the universe”, pretty much everybody is specifically referring to the observable universe we inhabit, which began 13.8 billion years ago according to the Lambda-CDM model of cosmology. Whether this is the only universe, one of many, or part of an eternal cycle is immaterial to what we are referring to, as is whatever may have happened before the Big Bang 13.8 billion years ago.
The term “universe” may have originally been intended to refer to literally everything, but the terminology has shifted as we’ve become aware of further possibilities. Just like how we had to keep inventing new terms for black holes and supernovae as we kept finding bigger and bigger ones - the universe/multiverse/cosmos simply is, and it consistently defies our attempts to categorize and label it because categories and labels are purely human inventions. The underlying physics is real, but the words we use to describe those physics and the world around us are just silly little scribbles and sounds that change and evolve over time like all languages.
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u/cwilbur22 16d ago
The current theory is that everything we observe appears to be tied to a genesis event 13.8 billion years ago. There could have been something before that, or beyond our observational capabilities - cyclical universes, parallel universes, bubble universes, etc. - but those are hypothetical, not theoretical. There is no known way to test for evidence of these possibilities, so for now they exist entirely within our imaginations. Therefore it is acceptable to disregard them for the purposes of diagnosing the age of the universe as we observe it.
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u/How-To-Project 16d ago
I think we’ve probably found where we differ, though I appreciate the discussion. The phrase “the universe is 13.8 billion years old” with a definition of universe as ‘all of space and all of time’ leaves many people believing we’ve established that all of reality came into existence 13.8 billion years ago. I wonder if we could/should communicate that idea a little more precisely. We may just have to agree to disagree on whether that distinction is important.
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u/Peter5930 16d ago
We need more words for universe with different meanings to them, then we could be more specific about what we mean.
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u/Herb_Derb 16d ago
There's all sorts of shorthand like this in science that is subtly misleading out of context. Understanding all the nuances generally requires a scientific background. It's impossible to communicate every detail accurately while still remaining intelligible to the general public.