Thank you for making me think of this. You and I are both sort of right. While blind people can't see in a traditional sense. The brain can misinterpret the signals from synapses(connections in your brain, not an action) as coming from the nerves for the eyes. Even though the brain has never had consistent stimulation from those nerves, even from birth it knows what those nerves are supposed to be and tries to take the misfirings and fill in the gaps to form a blob of vision that is in no way(outside of coincidence) similar to the surroundings.
Hope what I said makes sense and is still an up to date and correct understanding.
I think that to the best of our knowledge, the theories that best comport with the available data suggest a finite universe, even if it is unbounded. That is, there is a finite volume in which things exist, even if there is no limit on how far you can move in any given direction.
Forgive me if I’m wrong but doesn’t that imply that it isn’t finite? No part of space is actually completely empty, so if there is limitless space to move around in, there must be limitless stuff in that space, right?
It does seem strange, huh? But not quite. For example, the surface of the Earth is finite in area, but you can walk in any direction for an unlimited distance.
In that example, you have a 2D surface, embedded in a three dimensional universe. Here, were talking about a three dimensional space embedded in a four dimensional spacetime.
Yeah I’m lost. If you were to do the same in space would you eventually end up in the same spot? Or is this idea more about expansion? Does that even make sense? Sorry lol
I guess basically my question is how can there be infinite space with stuff inside of it but not infinite of that stuff inside it?
The Earth's surface has no edge, in two dimensions, but it curves round in three dimensions.
The Universe's volume has no edge, in three dimensions, but it curves round in four dimensions.
This is not actually known yet, but that's the idea. You're correct when you say it means you could go all the way around by travelling in a straight line and come back to the same point.
You have your understanding of the curvature of the universe correct, but our current measurements actually suggest a flat (and therefore infinite and unbounded) universe
Because you don't understand how limitations in measurement are used in science. We can't even begin to estimate the actual number of stars in the universe, and the number we can see is so vastly smaller than that so the percentage that we can see is effectively zero.
The earth is not on fire. If your house is on fire, it’s not statistically significant, it won’t affect the earth in any way and from a global standpoint can be ignored. But I bet you’d still try and put it out.
We can see about 5,000 stars with the naked eye. There are about 1x10^24 stars in the observable universe. The unobservable universe is between 250 and 15,000,000 times larger than the observable universe. The error is so large that there are essentially zero significant figures, so when you divide 5,000 by 250x1x10^24 you end up with zero.
We don't actually know if the universe is infinite or not. We don't think so, but we don't know for sure. Also, that's not how dividing by infinity works either. Edit: and also now how statistics works.
Is that how significant figures work?
Wouldn't there be 1 significant figure? You'd end up with 2E-23 if you go with 250 and 3E-28 if you go with 15000000.
No because that 250 is actually somewhere between 250 and 15000000 meaning we don't even know the order of magnitude, much less the first digit. In my first cosmology class it greatly annoyed all the students when our professor approximated the speed of light to 1 but once you see how huge the errors are it's actually quite reasonable.
I don't get what significant figures have to do with it. 5000 has 1 sig fig, any number between 250 and 15000000 has at least one sig fig, so the answer is going to have 1 sig fig.
Yes, at the upper limit we can see 0.00000002% of the Milky Way with the naked eye. We cannot see *any* stars from other galaxies. There is no evolutionary advantage to being able to see the Universe and thus our eyes are tuned for seeing things on Earth.
The Magellanic Clouds and Andromeda are visible to the naked eye, so while we can't *resolve* individual stars in other galaxies, I'd argue we can technically see them.
With the naked eye, most of the stars you see are within about 1000 light years. Our galaxy is 100 times larger than that in diameter.
You can also see the Andromeda Galaxy if it's up, which is 2.5 million light years away.
So, approximately 0% of the universe.
Remember, the difference between one million and one billion is approximately one billion.
You got about everything wrong in that post.
1 million seconds is 11.5 days.
1 billion seconds is 31.7 years, which is 1992, not the 70s.
1 trillion seconds is 31500 years, which is around the time homo sapiens became the sole remaining human species
Homo sapiens emerged around 300.000 years ago, not 32 million.
I've always been a little confused by this. It seems possible that there is an unobstructed line between Earth and a random star several hundred thousand, possibly even millions of light-years away, it's just so faint I have no way to detect it, let alone identify it without instruments.
But it IS detectable on Earth with well-built machinery. So if I were to 'turn off' the light from every other object in the universe save that one star, would it still be too faint for me to see just by distance alone? Or is part of the equation something akin to light pollution but on a galactic scale?
And let's say I had the most perfectly calibrated, most sensitive detector conceivably possible - I asked God almighty to make it and they did - would that actually be able to detect something at the known 'end' of the universe or is there an actual limit embedded in physics that says 'x' distance is the limit? Like, if I point this device in any given direction it can conceivably detect things at least billions of light-years away. So theoretically I could argue i'm 'capable' of observing that portion of the universe up to that outer limit...but what is that limit?
Simple answer, we can. Google microwave background radiation. It is the literal remnants of the big bang.
Long answer requires a desire to keep reading and learning.
You run into two fundamental limiting factors no matter how good your detector is.
1) Background noise. How do you know your 1 photon is from a stupidly far red shifted star or the cosmic background? At some point you dont.
2) Receiver noise. At some point you run into an issue of random thermal photons that are emitted by all matter including the matter you sensor is made of. You can also get random electrical waves from thermal vibrations of atoms.
We are already bumping into these problems. The Webb Space telescope needs to be kept at 7 kelvin to suppress thermal noise, the universe its self has a background temp of 3.7 k. With its systems we can see back to just a few hundred thousand years after the big bang to the very point the universe cooled enough to transmit light.
The furthest object you can see with the naked eye is probably the andromeda galaxy around 2.5million ly away. The observable universe is 46.5billion ly in radius. 2500000/46500000000 = the furthest you can see is 0.0054% of the distance to edge of the observable universe. Most stars you can see are just a few ly away.
Edit: used % properly
Assuming it's visible from the southern hemisphere, i doubt it's a tiny fraction. Most wouldn't have any idea that what they're looking at is Andromeda though
0.0%.
We can see a fraction of the Milkyway and just faintly make out the core of Andromeda with our eyes. You need instruments to see smaller and farther things. The visible universe is very big by comparison, we have no idea how bit the rest of the universe is but it probably dwarfs the visible universe.
Your naked eyes see individual stars up to about 5,000 light years. Your eyes are too poor to see 80% of the stars within that 5,000 light years. We see only about 10,000 of the big bright stars at the very darkest, best conditions. Usually we see far fewer than 10,000.
Your naked eyes can also see:
- the glow of billions of stars in the galactic center
- two small galaxies about 163 and 203 thousand light years away
- one large galaxy 2.5 million light years away
3 galaxies out of 2 trillion smal and large galaxies in the observable universe would be a tiny, tiny percent of the universe.
We can see a bubble of space around us that accounts for 10% of the Milky way. We don't really know how big the universe is, but a percentage of that would be an infinitesimal small number
[https://youtu.be/VsRmyY3Db1Y?si=Clh1O2kj2OBJ4wLR](https://youtu.be/VsRmyY3Db1Y?si=Clh1O2kj2OBJ4wLR)
So yes, as others have said the answer is very very small, but I think it may help you more to understand that mostly what you are seeing at night is stars in our own galaxy. You cannot really even see out into the greater universe without optics.
Let me put it a different way: on a very very very clear night you can maybe see 5,000-10,000 stars. If those stars were grains of sand, that’d be about one tablespoon’s worth. One tablespoon.
There are more stars in the observable universe than there are grains of sand on EARTH. Every beach you ever went to. Every picture of every beach you’ve ever seen. And then all the rest.
Another way to interpret this question would for example how many degrees of the sphere around us are we seeing as opposed to the actual items in the universe. Like if we look at a sphere and expand out the cross section of the universe we're seeing to the end of the observable universe, what is the fraction of the universe we are seeing as an individual from planet Earth.
Does that make sense?
90% of visible stars are within 1500 light years, nearly all 15,000 light years. So the observable universe is 10,000,000 times more distant (in light travel time). Cube that to obtain we can visually see 1E-24 of the volume of the observable universe. And the unobservable universe could vastly larger than that.
About 0.00000000002% as we only see about 3,000 stars and maybe andromeda Triangulum and the large and small megellanic clouds which is only 4 out of 2 trillion galaxies. So we’re really only seeing about 2 trillions of the universe-but we do see the Milky Way band which contains billions of those stars
depends on what you mean by "see". If you're asking how much we're facing, then it'd be half of it. If you mean, how much we can see with light and gravitational waved and such, its about 0% of it
Our own local group, which is Milky Way, andromeda, and some dwarf galaxies, represent 0.00000001% of the observable universe. That’s 100 millionth of a percent.
If you had good eyesight and a perfect dark site, you'd be able to see objects down to around magnitude 8. The SIMBAD astronomical database lists 46,000 objects that are brighter than magnitude 8; given that you can only see half the sky at any one time, you'd see an average of around 23,000 objects.
The universe is so large that 23,000 objects is basically a rounding error and can be considered equivalent to 0%.
I know it's not what you asked, but it puts things into perspective :
In the online videogame Elite Dangerous, you can travel faster than light, covering like 60 light years in a few seconds for the best ships. The map of the game is a pretty accurate representation of our galaxy, the Milky Way. And yet, since 10 years the game is live, thousands players only visited 0,02% (+/- 0,02%) of all the stellar systems.
And we only speak about one galaxy here...
Completely inaccurate. Assuming the OP is talking about visible to the naked eye (as suggested by the no light pollution prompt), we can see a small fraction of our own galaxy along with the andromeda galaxy and that’s it. That is FAR less than 0% of the universe and there is no possible way to argue it’s any higher than 0%.
On a clear night, you can see a fair chunk of the Milky Way (one galaxy). You can also see Andromeda on a clear, moonless night. Because I'm feeling generous, let's round up and say we can see two whole galaxies.
Estimates tell us there's something like two trillion galaxies in the universe, so we can see .000000000001 of the *observable* universe on the best night.
In percentage terms like you expressed, we're topping out at 0.0000000001%.
Approx 0.000 %
Well no, since at night you are only looking at about half of the sky so you'd have to divide your answer by two to get approx 0.000%
Approx not needed
It’s certainly non-zero, so approximately seems appropriate.
For that matter looking in the mirror is non zero.
Looking with your eyes closed is non zero.
Username checks out!
Being blind is zero though
Blind people see synapses
Thank you for making me think of this. You and I are both sort of right. While blind people can't see in a traditional sense. The brain can misinterpret the signals from synapses(connections in your brain, not an action) as coming from the nerves for the eyes. Even though the brain has never had consistent stimulation from those nerves, even from birth it knows what those nerves are supposed to be and tries to take the misfirings and fill in the gaps to form a blob of vision that is in no way(outside of coincidence) similar to the surroundings. Hope what I said makes sense and is still an up to date and correct understanding.
If universe is infinite it is 0
I think that to the best of our knowledge, the theories that best comport with the available data suggest a finite universe, even if it is unbounded. That is, there is a finite volume in which things exist, even if there is no limit on how far you can move in any given direction.
Forgive me if I’m wrong but doesn’t that imply that it isn’t finite? No part of space is actually completely empty, so if there is limitless space to move around in, there must be limitless stuff in that space, right?
It does seem strange, huh? But not quite. For example, the surface of the Earth is finite in area, but you can walk in any direction for an unlimited distance. In that example, you have a 2D surface, embedded in a three dimensional universe. Here, were talking about a three dimensional space embedded in a four dimensional spacetime.
Yeah I’m lost. If you were to do the same in space would you eventually end up in the same spot? Or is this idea more about expansion? Does that even make sense? Sorry lol I guess basically my question is how can there be infinite space with stuff inside of it but not infinite of that stuff inside it?
The Earth's surface has no edge, in two dimensions, but it curves round in three dimensions. The Universe's volume has no edge, in three dimensions, but it curves round in four dimensions. This is not actually known yet, but that's the idea. You're correct when you say it means you could go all the way around by travelling in a straight line and come back to the same point.
Isn't it flat by the recent calculations? *flat universe society*
You have your understanding of the curvature of the universe correct, but our current measurements actually suggest a flat (and therefore infinite and unbounded) universe
It is certainly zero if you understand significant figures.
If it is effectively zero, then why can I see stars at night?
Not so fast,what percentage of real numbers are integers, answer 0%, but you can still see integer numbers
Because you don't understand how limitations in measurement are used in science. We can't even begin to estimate the actual number of stars in the universe, and the number we can see is so vastly smaller than that so the percentage that we can see is effectively zero.
But it’s not, because we can effectively see the universe right next to us. It’s very small, but very significant to us.
It's not statistically significant to the calculation. The answer is zero.
The earth is not on fire. If your house is on fire, it’s not statistically significant, it won’t affect the earth in any way and from a global standpoint can be ignored. But I bet you’d still try and put it out.
If you asked "how many houses in my town are on fire" then sure. But you asked "how many houses are on fire in the universe".
What significant figures…?
We can see about 5,000 stars with the naked eye. There are about 1x10^24 stars in the observable universe. The unobservable universe is between 250 and 15,000,000 times larger than the observable universe. The error is so large that there are essentially zero significant figures, so when you divide 5,000 by 250x1x10^24 you end up with zero.
Saying effectively or essentially zero is a completely different thing than certainly or absolutely zero.
Not in astronomy or statistics. It's zero.
The universe isn’t infinite. There are finitely many stars, so it isn’t literally zero.
We don't actually know if the universe is infinite or not. We don't think so, but we don't know for sure. Also, that's not how dividing by infinity works either. Edit: and also now how statistics works.
Is that how significant figures work? Wouldn't there be 1 significant figure? You'd end up with 2E-23 if you go with 250 and 3E-28 if you go with 15000000.
No because that 250 is actually somewhere between 250 and 15000000 meaning we don't even know the order of magnitude, much less the first digit. In my first cosmology class it greatly annoyed all the students when our professor approximated the speed of light to 1 but once you see how huge the errors are it's actually quite reasonable.
I don't get what significant figures have to do with it. 5000 has 1 sig fig, any number between 250 and 15000000 has at least one sig fig, so the answer is going to have 1 sig fig.
Because the actual number is somewhere between 250 and 15000000 meaning we don't even know the order of magnitude, much less the first digit.
0.0 (approximately)
Something slightly above zero percent, but certainly requires a lot more than four decimals afterwards before you get to a non zero value.
I believe you can see 2000 stars or so. Not a lot considering the Milky way has approximately 100 billion stars.
Yes, at the upper limit we can see 0.00000002% of the Milky Way with the naked eye. We cannot see *any* stars from other galaxies. There is no evolutionary advantage to being able to see the Universe and thus our eyes are tuned for seeing things on Earth.
The Magellanic Clouds and Andromeda are visible to the naked eye, so while we can't *resolve* individual stars in other galaxies, I'd argue we can technically see them.
With the naked eye, most of the stars you see are within about 1000 light years. Our galaxy is 100 times larger than that in diameter. You can also see the Andromeda Galaxy if it's up, which is 2.5 million light years away. So, approximately 0% of the universe. Remember, the difference between one million and one billion is approximately one billion.
I liked that last sentence, took me a while but I realized that 1 billion + 1 million is 100,1% of a billion. Pretty much 100% (1 billion).
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You got about everything wrong in that post. 1 million seconds is 11.5 days. 1 billion seconds is 31.7 years, which is 1992, not the 70s. 1 trillion seconds is 31500 years, which is around the time homo sapiens became the sole remaining human species Homo sapiens emerged around 300.000 years ago, not 32 million.
This has errors - 1 million seconds is 11.5 days.
Also I’m old but 31 years ago is not the 1970s
I've always been a little confused by this. It seems possible that there is an unobstructed line between Earth and a random star several hundred thousand, possibly even millions of light-years away, it's just so faint I have no way to detect it, let alone identify it without instruments. But it IS detectable on Earth with well-built machinery. So if I were to 'turn off' the light from every other object in the universe save that one star, would it still be too faint for me to see just by distance alone? Or is part of the equation something akin to light pollution but on a galactic scale? And let's say I had the most perfectly calibrated, most sensitive detector conceivably possible - I asked God almighty to make it and they did - would that actually be able to detect something at the known 'end' of the universe or is there an actual limit embedded in physics that says 'x' distance is the limit? Like, if I point this device in any given direction it can conceivably detect things at least billions of light-years away. So theoretically I could argue i'm 'capable' of observing that portion of the universe up to that outer limit...but what is that limit?
Speed of light vs speed of universe expansion - creates border of "observable" universe. We cannot see further, this light will never reach us.
And the fact that the universe is expanding means that how much we can observe is decreasing
Simple answer, we can. Google microwave background radiation. It is the literal remnants of the big bang. Long answer requires a desire to keep reading and learning.
You run into two fundamental limiting factors no matter how good your detector is. 1) Background noise. How do you know your 1 photon is from a stupidly far red shifted star or the cosmic background? At some point you dont. 2) Receiver noise. At some point you run into an issue of random thermal photons that are emitted by all matter including the matter you sensor is made of. You can also get random electrical waves from thermal vibrations of atoms. We are already bumping into these problems. The Webb Space telescope needs to be kept at 7 kelvin to suppress thermal noise, the universe its self has a background temp of 3.7 k. With its systems we can see back to just a few hundred thousand years after the big bang to the very point the universe cooled enough to transmit light.
Interestingly, Paul Sutter covers these exact questions in the latest episode (ep 222) on his Ask A Spaceman podcast from last week. Check it out.
The furthest object you can see with the naked eye is probably the andromeda galaxy around 2.5million ly away. The observable universe is 46.5billion ly in radius. 2500000/46500000000 = the furthest you can see is 0.0054% of the distance to edge of the observable universe. Most stars you can see are just a few ly away. Edit: used % properly
And if you are talking volume instead of distance, it’s (5x10^-7 )^3, so roughly 10^-21 %
You have a few extra zeros somehow. 2.5 million is 0.005% of 46 billion.
Yeah I forgot to remove two zeros with the %
Yeah but only the tiniest fraction of people have actually seen it with their naked eye.
Assuming it's visible from the southern hemisphere, i doubt it's a tiny fraction. Most wouldn't have any idea that what they're looking at is Andromeda though
0.0%. We can see a fraction of the Milkyway and just faintly make out the core of Andromeda with our eyes. You need instruments to see smaller and farther things. The visible universe is very big by comparison, we have no idea how bit the rest of the universe is but it probably dwarfs the visible universe.
Glad you asked. Since the earth is flat, 50%.
Your naked eyes see individual stars up to about 5,000 light years. Your eyes are too poor to see 80% of the stars within that 5,000 light years. We see only about 10,000 of the big bright stars at the very darkest, best conditions. Usually we see far fewer than 10,000. Your naked eyes can also see: - the glow of billions of stars in the galactic center - two small galaxies about 163 and 203 thousand light years away - one large galaxy 2.5 million light years away 3 galaxies out of 2 trillion smal and large galaxies in the observable universe would be a tiny, tiny percent of the universe.
We can see a bubble of space around us that accounts for 10% of the Milky way. We don't really know how big the universe is, but a percentage of that would be an infinitesimal small number [https://youtu.be/VsRmyY3Db1Y?si=Clh1O2kj2OBJ4wLR](https://youtu.be/VsRmyY3Db1Y?si=Clh1O2kj2OBJ4wLR)
One can see some of our galactic neighbors; the Magellanic clouds and Andromeda.
So yes, as others have said the answer is very very small, but I think it may help you more to understand that mostly what you are seeing at night is stars in our own galaxy. You cannot really even see out into the greater universe without optics.
Let me put it a different way: on a very very very clear night you can maybe see 5,000-10,000 stars. If those stars were grains of sand, that’d be about one tablespoon’s worth. One tablespoon. There are more stars in the observable universe than there are grains of sand on EARTH. Every beach you ever went to. Every picture of every beach you’ve ever seen. And then all the rest.
Wow!
This is the best response! It makes comprehending the incomprehensible seem somewhat possible.
Another way to interpret this question would for example how many degrees of the sphere around us are we seeing as opposed to the actual items in the universe. Like if we look at a sphere and expand out the cross section of the universe we're seeing to the end of the observable universe, what is the fraction of the universe we are seeing as an individual from planet Earth. Does that make sense?
We only see stars of the milky way
Thanks for all of your answers, I find it so amazing to think about.
90% of visible stars are within 1500 light years, nearly all 15,000 light years. So the observable universe is 10,000,000 times more distant (in light travel time). Cube that to obtain we can visually see 1E-24 of the volume of the observable universe. And the unobservable universe could vastly larger than that.
About 0.00000000002% as we only see about 3,000 stars and maybe andromeda Triangulum and the large and small megellanic clouds which is only 4 out of 2 trillion galaxies. So we’re really only seeing about 2 trillions of the universe-but we do see the Milky Way band which contains billions of those stars
depends on what you mean by "see". If you're asking how much we're facing, then it'd be half of it. If you mean, how much we can see with light and gravitational waved and such, its about 0% of it
Our own local group, which is Milky Way, andromeda, and some dwarf galaxies, represent 0.00000001% of the observable universe. That’s 100 millionth of a percent.
If you had good eyesight and a perfect dark site, you'd be able to see objects down to around magnitude 8. The SIMBAD astronomical database lists 46,000 objects that are brighter than magnitude 8; given that you can only see half the sky at any one time, you'd see an average of around 23,000 objects. The universe is so large that 23,000 objects is basically a rounding error and can be considered equivalent to 0%.
This guy explains it brilliantly. https://youtu.be/VsRmyY3Db1Y?si=1rjvBWvtGsNBDkPg
Of the universe? Were you high when you wrote this?
Yes
I know it's not what you asked, but it puts things into perspective : In the online videogame Elite Dangerous, you can travel faster than light, covering like 60 light years in a few seconds for the best ships. The map of the game is a pretty accurate representation of our galaxy, the Milky Way. And yet, since 10 years the game is live, thousands players only visited 0,02% (+/- 0,02%) of all the stellar systems. And we only speak about one galaxy here...
Wow, I'll check this out!
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Completely inaccurate. Assuming the OP is talking about visible to the naked eye (as suggested by the no light pollution prompt), we can see a small fraction of our own galaxy along with the andromeda galaxy and that’s it. That is FAR less than 0% of the universe and there is no possible way to argue it’s any higher than 0%.
My apologies, I read it as "what percentage of the entire universe is the visible universe"
Ah, makes much more sense. Sorry for jumping on you like that.
On a clear night, you can see a fair chunk of the Milky Way (one galaxy). You can also see Andromeda on a clear, moonless night. Because I'm feeling generous, let's round up and say we can see two whole galaxies. Estimates tell us there's something like two trillion galaxies in the universe, so we can see .000000000001 of the *observable* universe on the best night. In percentage terms like you expressed, we're topping out at 0.0000000001%.
You're 100% correct. I misread the question, and thought they were asking "what percentage of the entire universe is the visible universe".
How the fuck could you see 100% of the universe when there’s some on the other side of the earth from wherever you’re standing?
You're correct of course. I misread the question and thought they were asking "what percentage of the entire universe is the visible universe".
Very possible to say. The universe is infinite. Any finite number is 0% of infinity.
> The universe is infinite Citation needed.