Submitted by Tatti_luck t3_yhizh0 in space
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Comments
boundegar t1_iuf5qef wrote
It will never reach us. Lonely thought.
[deleted] t1_iufk02e wrote
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Tatti_luck OP t1_iugbabt wrote
Then how do we know that as of now 45 billion light years is the edge?
patco81 t1_iue1204 wrote
Now you have me wondering too.
Can't wait for some rocket surgeons to answer this one.
No_Masterpiece6568 t1_iue4qz7 wrote
You have a misconception in your understanding of the expansion of space. All space is expanding but at different rates according to how far away from us the observed object is. So for instance, the space between us and the sun is expanding, but at a much slower rate than the rate between us and distant objects. Distant objects have more space between us and them, and therefore more rapid expansion. The only limit to our observations is the resolution of our telescopes. Even galaxies that formed just after the Big Bang are observable, but because they are so far away their light has been red shifted into the infrared, and therefore we need an infrared telescope to observe them (hence the Spitzer telescope, which will make observations right up to the Big Bang event).
Tatti_luck OP t1_iugbqmq wrote
So even our current telescopes have a limitation and the most we can see is till the BB. Then how do we know that there is something beyond the horizon? Shouldn’t our view be limited to 14 billion years in radius?
Varlex t1_iue7brl wrote
>I know as a fact that the expansion of space is faster than the speed of light. But how do we know that?
That's not fully true. The expansion of the universe scales up with distance.
Current measurement of hubble constant is 68 - 74 km/s/Mpc.
That means, a object in a distance of 1Mpc "move away" by 68-74 km/s. ==> For objects next to us it's less, for objects far away it's more.
Next, there is a event horizon, when the distance is so large, that the expansion is larger in distance per seconds then 300000km/s (light speed). For Objects behind this event horizon, light can't go to earth and we don't get any new information.
For your second question and why is the (visible) universe 93 billion lightyears in diameter and just 14 billion years old.
Same reason, in the beginning the (visible) universe was much smaller. An object send out photons. This photons "travel" in our direction. Because the universe expand, the way between object and our location increase. When the light is measured on earth, the object is much more far away, when the photon was send out.
rE3eYul t1_iuewo39 wrote
but wouldnt those objects that travel faster then light being on the edge of the expansion be physical , i.e be made of mater , how about relativity ?
Varlex t1_iuey1gr wrote
They don't travel faster then light. The room between expend.
It's like you stretch slowly a rubber band. The distance between ends of the band increase faster then somewhere in the middle.
The expansion of the universe don't interfere SRT or ART. Lightspeed is still lightspeed, but when expansion is bigger then 300k km/s, the light can't brigde over the whole way.
[deleted] t1_iueyq8b wrote
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Tatti_luck OP t1_iugcc6u wrote
I understand that the light traveling to us would be what it was years ago compared to their current relative position. But how do we know that currently position is much further than we are viewing? Would we be seeing the increase in distance in real time?
Varlex t1_iuh34kr wrote
It's the red shift.
There are 2 models for light: particles and wave. Both are equal and correct.
Because room is expending, the wave length increase. Depending how much it increase we can calculate how long it's needed and can calculate the different distances with this information.
(It's like the Doppler effect with sound)
Tatti_luck OP t1_iuk9s6v wrote
Thanks that helps
Applejuiceinthehall t1_iuej0z8 wrote
>As you said space expands f>I know as a fact that the expansion of space is faster than the speed of light. But how do we know that?
We know that space is expanding faster because of the dipper effect. You probably are most familiar with how a siren sounds differently to you if it's approaching or moving away from you. Well light has that effect too. So we see that the light is shifted to the moving away from us. The objects farther away from us has a greater shift in their light than closer objects. So that's how we know it's moving faster than
>How do we know that the observable universe is 90 billion light years across. Wouldn’t it take 45 billion light years for the light to reach us? (assuming we are at the center for argument sake) If the universe itself is 14 billion years old, wouldn’t we have to wait another 31 billion years to know the space expanded?
When the light left galaxies, they were 14 billion light years away but now they are 46 billion light years away.
Try to imagine you are standing on a road in front of you every meter there is a person standing, behind you there is also a person every meter. The road starts to expand so now there is an extra meter between every person. So the person 1 meter in front of you is now 2 meters in front of you. The person that was 10 meters from you is now 20 meters away.
Put another way the farther away someone is the faster they appeared to move despite no one moving at all
Now imagine there a car on the road as it sets out we know how far away the destination but as they arrive at their destination we see that it takes longer than it should have because the road expanded while they were moving. Some destinations are so far the car won't ever reach it no matter how fast they go.
If a similar car was coming towards us and we could observe (we couldnt) it would appear like the car was moving away from us even though it's clearly moving towards us.
So for your questions even though the light was emitted 13.8 billion years ago the space between where it was emitted and where we are has expanded since that time and they are 46 billion light years away.
Varlex t1_iuekwlq wrote
>When the light left galaxies, they were 14 billion light years away but now they are 90 billion light years away.
That's not true, also the space between light and goal expend.
The current star with the most distance exists 900000000 years after bigbang and is now 12,9 billion light years away. But when the photon was send out, it was 1,75 billion light years away. The light needs 13 billion years to travel to our position. (Z = 6,2)
Opening_Customer_665 t1_iue16ba wrote
Great question, and put in words for average people to fathom , Ty.
ChrisARippel t1_iue8833 wrote
Don Lincoln's videos help me answer your questions
Zeduca t1_iuedm4s wrote
Do we know as a fact now that space is expanding faster than speed of light, or even accelerating ?
NotAHamsterAtAll t1_iuera7a wrote
No, but it is part of the "best" theory that cosmologist have at the moment.
This "best" theory manages to explain about 5% of the world, the rest needs Dark Fudge ^(TM) to work.
AhRedditAhHumanity t1_iueqimn wrote
If it’s expanding faster than light, then no, it wouldn’t take 45 billion light years to reach us. It would never reach us. Faster than light away plus speed of light towards equals net away.
rE3eYul t1_iuevq5r wrote
you are assuming you are at the center of it all , we are not , we see the "visible universe" basically a bubble within the universe, but there is older light that hasn't got to us yet , some will never get to us
SpartanJack17 t1_iufl0hl wrote
Hello u/Tatti_luck, your submission "Please explain in simple words" has been removed from r/space because:
- Such questions should be asked in the "All space questions" thread stickied at the top of the sub.
Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.
ExtonGuy t1_iue8sjv wrote
It didn’t/ doesn’t take 14 billion years for the light from the BB to reach us. We (the material that became us) came into existence inside the BB … in the middle of an infinite space. The light from the BB started hitting us immediately, from all directions. It has been hitting us ever since. The light that is hitting now has been traveling for 14 billion years. It comes from a distance that used to be a lot closer, but is now 46 billion light-years away.
(Much simplified, but I hope not too misleading.)
[deleted] t1_iue1ah5 wrote
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Opening_Customer_665 t1_iue1qks wrote
You just annoy me . You explain absolutely nothing of worth
Tatti_luck OP t1_iue3gtw wrote
You realize that not everyone is an expert and some are just trying to seek answers to something we want to understand? If a kid asks you something out of curiosity, would you try to explain them in simple words or tell them that the answer is out there somewhere but nothing you’d understand so you’re stupid.
[deleted] t1_iue3wti wrote
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Nerull t1_iue5ytf wrote
45.7 billion light-years is the current comoving distance to the edge of the visible universe - this distance includes expansion. It is the distance now, not the distance when the light we are seeing was emitted. The observable universe was smaller when the light we are seeing now was emitted, because that light has taken time to reach us.
The light being emitted now from objects at the edge of the observable universe will not reach us for a very, very long time - much longer than 45 billion years, because the space in between us and that light will expand even more while it is traveling. Light traveling from 45 billion light years away will have to travel further than 45 billion light years to reach us.