with how light works and the constant expansion of what we term the “observable universe” why don’t we constantly see new stars appearing in the night sky as the observable part expands and stars/galaxies light reaches us for the first time?
The night sky has stayed relatively the same (accounting for changing postions over time, stella phenom, supernovas etc.) for all of humans written history.
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The universe is expanding faster than the light is travelling so it’s getting farther away.
I think the best way to visualise the expansion is to think of a ballon full of dots on its surface, each dot representing a galaxy. And when you blow the ballon up those dots moves further and further apart.Now we will notice that the speed of the expansion between two neigboring dots is X, but if we look at dots that are 2 places apart, they move apart at 2X speed. Same applies for galaxis in that the further away something is from us, the faster it is also moving away from us because theres more space between us that is continually expanding itself.
Now imagine our observable universe is a set distance on this balloon thats as far as we can currently see before expansion exceeds the speed of light. Think of a circle that isnt stuck to the ballon but just a physical circle we lay on the baloons surface. As we blow it up more and more dots will move from inside this circle circumference to outside of it. Same goes for galaxies, as time goes on less and less galaxies will be observable.
In 10-30 billion years a civilization of similar tech as we do would probably only be able to detect its local galaxy cluster and come to very different conclusions about the universe then we have. Fast forward further and a civilization would proclaim their glaaxy to be all there is.
Now im not sure i understood completely but it sems this expansion isnt constant but are growing. So one hypothesis is that this expansion will eventually win out gravity and even the molecular forces in the end. Scatter the galaxies, solarsystems, planets and at last break apart the individual atoms… Sounds insane but who knows… ive not looked into the math behind it.
Any new Star light to reach us would be from the new furthest star which would be the new dimmest star in the sky. Even under the best viewing conditions we can only see a very small fraction of stars from earth so these new stars would certainly not be bright enough to be seen.
Our galaxy is 105,700 light years across. We can “see” the entire width from earth already. Stars in other galaxies are too dim to see with the naked eye.
Using telescopes, we can already see loads of other galaxies as well. But the distance between galaxies is often another 100,000 light years (or more!). So new ones aren’t “added” to our field of vision very often.
I have so many questions after reading the comments/answers!… (I’m a layman.) How can objects at the edge of the universe be expanding faster than the speed of light if as an object approaches the speed of light its mass increases exponentially? Are some objects actually becoming massive, or can they not exceed the speed of light bc of this? Or is “massive” just a relative term within e=mc^2 and their actual mass isn’t really increasing? And if things are getting more massive, will they start attracting each other more causing the universe expansion to slow and eventually reverse and contract, or is that not possible bc now the objects are too far from each other for gravity to matter much? And if there’s no true center and every object is at its own center of the universe, then aren’t there infinite “edges of the universe” in which case, which objects are passing the speed or light, or are we all passing the speed of light just relative to some objects (really distant ones) and not others (really close ones). Lastly, since we’re all at our own relative center of the universe, can we really not extrapolate to know what is the true center where the Big Bang originally happened?
If we had a perfect resolution of the light -in all wavelengths-coming towards us, then that is what we would see.
The cosmic background radiation is visible in every direction, because that’s literally the remnants of the Big Bang. This means we’re enveloped in an ever-expanding bubble of this cosmic background radiation. This is the extreme of what we can detect.
After the big bang, there was some time that passed until the universe cooled enough to be see-through, and after even more time the first stars began to give off light.
These stars are technically the oldest things we could theoretically detect, but the light from them has travelled for billions of years, weakening it immensely, and space has expanded in that timeframe making it shift to the lower-energy end of the spectrum.
The light also must get to us without anything passing in between that can obstruct it.
So you have a very weak signal, at very low energy levels with a high chance of being obstructed.
In spite of that, with the new James Webb space telescope we can see very far because the sensors are better than ever before. However they have limits of resolution and limits in what parts of the light-spectrum we can detect.
So why can’t we see everything? Because of objects that block the light, and hardware limits of the sensors.
If we didn’t have those problems, we would indeed see everything.
Light intensity decreases as a square of distance. this is because the light is spreading out as a sphere. light passing through one square unit of area on that sphere will be spread over 100 square units of area after passing ten units of distance from the source. Same idea as the shock from an explosion, in a way: up close, it is intense, but far enough away and you wouldn’t even notice it; don’t even hear it.
So, although there is lots of light coming from everywhere, most of it is just too faint to see. That is, if you go away in a straight line from here, you will eventually hit a star, because even though stars are pretty sparse in space, you have basically forever you can go, so eventually, odds are that your line of sight would hit a star. The sky would by bright everywhere if we could see it all.
But we cannot. We only see stars that are reasonably close (really close, mostly, although telescopes and other detection devices can “see” light at levels much lower than our eyes). Everything else is too faint to see.
If distant stars only sent light directly toward the earth, so the light was a straight beam and did not decrease intensity with distance (working like a laser, sort of), then sure, we could read at night using that starlight. But stars do not send all their light in one thin line directly toward the earth. Only the tiny part of the output of a star follows that super-thin line from there to here; the rest ends up somewhere else. We will never see most (essentially all) of the light from most stars, for this reason. We only get a tiny, tiny, tiny, tiny portion of their light. Not enough for our eyes to see. And the further away it comes from, the way lower amount we will ever get. Still some, though.
Inverse-square law.
ELI5: Imagine a ball made of light. There is a certain amount of light on the outer surface of that ball. If the ball grows and gets twice as big, the light spreads out in two directions. Instead of half as much light in a given area, there is one-quarter as much light.
As you get further away, the amount of light you could see drops off very, very quickly. Ten times further away means 1/100th the light. Stars are very bright but very far away. We only see the closest and brightest stars in the night sky.
We can already see the stars that are close enough to see with our naked eyes. Their light got here billions of years ago. The ones whose light is just now reaching us are much, much too far away to see with anything less than the very best telescopes. It’s a big part of why we keep making better telescopes, and why we’re putting them into orbit now, to get a better look without air in the way.
On a clear night, go outside and look up at the sky. Find a patch of darkness, with no stars that you can see, and hold your hand out so your little finger covers it. The area covered by your little fingernail contains *billions* of galaxies that are just too far away for you to see them. If you had a really, really good telescope, that totally black spot would look like [this](https://www.nasa.gov/content/discoveries-hubbles-deep-fields). Those aren’t stars, they’re entire galaxies of stars.
They are not bright enough, they are too far away, there are brighter stars, or something else in the way.
Most stars are just not in the milkyway, making them impossible to see with the naked eye.
For a star to be visible, it needs to had a brightness of 6ish magnitude, moon is -13 and sun is -27.
There are hundreds of billions of stars in our galaxy…
But less then 10000 are visible to us with the naked eye.
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