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How Can a Star Be Older Than the Universe?

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Re: How Can a Star Be Older Than the Universe?

#161

Post by simiones »

pkofod wrote: post #143
kijin wrote: post #118

Earlier quoted context omitted.

No, it's observed as 93 billion light years. That's why we call it the "observable" universe. There is no meaningful spatial boundary at a point that is currently at a distance of 13.8 billion light years from us. We can detect (severely red-shifted) photons from beyond that point perfectly fine! The actual boundary is 46.5 billion light years away in both directions, hence the "observable" diameter of 93 billion. Bu…

I feel so stupid when talking and hearing about physics... but we are not in any meaningful way "at the center" of the universe are we? Or is every point in some sense at the center (a point of reference thing)? I'm asking because why would it be 46.5 "each way"?

We are by definition almost at the center of the universe that we can observe - we can see as far away in any direction.

Re: How Can a Star Be Older Than the Universe?

#162

Post by Hermel »

laurencei wrote: post #115
namirez wrote: post #65

Earlier quoted context omitted.

Also, despite the age of the universe (13.8B years), the diameter of the observable universe is 93 billion light years. That's because the universe expanded (and probably still is expanding) faster than light.

Can you ELI5 - how can we observe something 93 billion light years away, if the light has only been traveling for 13.8B years? Shouldnt the "observable" distance be the the age of the universe?

If someone in a train traveling at 108km/h throws a ball at you while passing and you catch the ball two seconds later, you also received a ball from someone “60 meters away” even though the ball only traveled a few meters. The point is: when the ball was thrown the train was much closer. Likewise, the other object was much closer when it sent out the light we see today.

Re: How Can a Star Be Older Than the Universe?

#163

Post by irishsultan »

pkofod wrote: post #143
kijin wrote: post #118

Earlier quoted context omitted.

No, it's observed as 93 billion light years. That's why we call it the "observable" universe. There is no meaningful spatial boundary at a point that is currently at a distance of 13.8 billion light years from us. We can detect (severely red-shifted) photons from beyond that point perfectly fine! The actual boundary is 46.5 billion light years away in both directions, hence the "observable" diameter of 93 billion. Bu…

I feel so stupid when talking and hearing about physics... but we are not in any meaningful way "at the center" of the universe are we? Or is every point in some sense at the center (a point of reference thing)? I'm asking because why would it be 46.5 "each way"?

We are at the center of the observable universe. And not that's not special, any star/galaxy is at the center of it's observable universe.

Re: How Can a Star Be Older Than the Universe?

#164

Post by doliveira »

lottin wrote: post #39

Here we go again... "scientists would look at the ripples in the fabric of space and time". Am I the only one who finds this expression very confusing? What fabric? There is no fabric. Space and time are coordinates. They do not exist physically at all. There cannot be a fabric of space and time.

Twists and turns like a fabric, waves like a fabric...

Re: How Can a Star Be Older Than the Universe?

#165

Post by noselasd »

ivoras wrote: post #144
ggggtez wrote: post #141

Earlier quoted context omitted.

No. Just because space is expanding doesn't change the electromagnetic forces holding you together.

But just thinking of the electromagnetic forces in terms of what is required from them to keep matter together in the context of that same matter effectively expanding faster than the speed of light is... at best weird.

It's not faster than light at the scale where there's matter in the universe. Across a planet or solar system it's not measurable.

It's when you measure between one side of the observable universe to the oposite side that the expansion speeds get crazy.

Re: How Can a Star Be Older Than the Universe?

#166

Post by mFixman »

rokalakt1337 wrote: post #150
namirez wrote: post #65

Earlier quoted context omitted.

Also, despite the age of the universe (13.8B years), the diameter of the observable universe is 93 billion light years. That's because the universe expanded (and probably still is expanding) faster than light.

So does this mean speed faster than light is possible?

The comparison that helped me understand it was seeing the Universe as a balloon.

My friend and I both live at different points on the surface of a balloon with distance A. I throw a ball at light speed while the balloon is being inflated, and the distance between us is B when the ball reaches him after T time.

To my friend it seems that the ball was thrown at B / T speed, which is faster than the speed of light.

Re: How Can a Star Be Older Than the Universe?

#167

Post by wruza »

crooked-v wrote: post #85
hirundo wrote: post #79

I think, by Occam's Razor, the most likely explanation is that there's a skybox surrounding the solar system that Voyager 1 may run into any day now, like Truman Burbank at the end of The Truman Show. It seems to be a more parsimonious explanation of the available facts that we're looking at the result of a super duper planatarium projector, as opposed to an actual vast and frequently inexplicable universe.

If you're going in that direction, you may as well say that the universe is a simulation. Planck limits on measuring time and space as a continuum would pretty useful for putting a hard cap on required rendering resources per volume of space-time...

Simulation doesn’t have to obey the rules. For non-scientists it is enough to “tell” them how it works without actually rendering it, cause they’ll never check. For scientists, you have to make their brain believe that all is consistent with complex computations all the way down.

Imagine that you know physics and math very good. But then simulation suddenly fails due to segfault and you realize that all your knowledge was just a gibberish nonsense and your work sessions and discussions were dream-like experience. Otherwise it was just a pretty dumb 3d simulation slightly better than a modern AAA game.

Edit: I mean, a simulation argument opens a huge can of worms, if you consider the perspective of a lazy simulation developer them-self.

Re: How Can a Star Be Older Than the Universe?

#168

Post by eru »

doliveira wrote: post #159
Aenyn wrote: post #157

Earlier quoted context omitted.

Wouldn't there be a delay between the time you flicked your wrist and the time the spot actually aligns, due to the limited speed of light?

Yeah, and observing this is a good way to see that information isn't actually being transferred faster than light.

Yep, definitely.

An outside observer that just sees the spot on the moon (but has no clue that it's produced by you flicking your wrists), just sees a spot that moves insanely fast.

No information, energy nor matter travels faster than light here, of course.

Re: How Can a Star Be Older Than the Universe?

#169

Post by philipov »

techas wrote: post #139
devnulloverflow wrote: post #116

Earlier quoted context omitted.

Your intuition that there is an limited observable distance because is correct. But because of the expansion, that limit is bigger than "speed_of_light * age of universe" . I don't know enough General Relativity to give a solid explanation. But here is a rough over-simplification: Imagine you've spent the last 5 seconds blowing up a balloon, but there is an ant walking on that balloon, starting from a marked spot. In…

If space works as a balloon then the growth happens in all the volume of the universe (not just on the “boundary”). Is that how it works? Doesn’t that imply that we are getting “bigger”?

Think of the expansion of the universe as a superlatively weak repulsive gravitational force that scales with the distance to an object. It is so weak at short scales that it is more weak than attractive gravity by a greater factor than attractive gravity is weaker than electromagnetism. It is so small at short scales that even the normal attraction of gravity is so much stronger as to make it undetectable.

However, at scales so large that gravitational attraction has attenuated to nothing, this repulsive component of gravity is still getting stronger. At the scale of galaxy clusters, it is pushing everything in the universe apart in all directions: faster the farther apart they are. At a certain distance, it becomes so strong that objects will appear to be moving away from you faster than the speed of light.

The distance at which that happens is called your Cosmological Horizon, and it has similarities to the event horizon of a black hole turned inside out. Unlike a black hole, however, there isn't a single unique event horizon. Every distinct gravitationally-bound object (galaxy cluster) in the universe has its own cosmological horizon; every other object is being pushed out towards it, and vice versa.

Re: How Can a Star Be Older Than the Universe?

#170

Post by brutt »

devnulloverflow wrote: post #116
laurencei wrote: post #115

Earlier quoted context omitted.

Can you ELI5 - how can we observe something 93 billion light years away, if the light has only been traveling for 13.8B years? Shouldnt the "observable" distance be the the age of the universe?

Your intuition that there is an limited observable distance because is correct. But because of the expansion, that limit is bigger than "speed_of_light * age of universe" . I don't know enough General Relativity to give a solid explanation. But here is a rough over-simplification: Imagine you've spent the last 5 seconds blowing up a balloon, but there is an ant walking on that balloon, starting from a marked spot. In…

Where is the waves? 13.8B years is too short to make Universe smooth again after such epic event. It's like to see green grass again just 1 second after nuke blast: mathematical formulas will need lot of magic constants for this to explain.
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