Calculating the Size of the Universe

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In summary, The universe is most likely infinite, and the radius of the observable universe is 47 billion lightyears. It is bigger than you might expect because space has expanded since those objects emitted the light that is now reaching us.
  • #1
Mattius_
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well i know I am wrong somewhere so show me where...

couldnt we calculate the size of the universe by taking the speed of light and the estimated age of the universe (14.5 billion years) and consequently use 14.5 billion light-years as a radius and put it into the old spherical volume equation (4/3 * pi * r3)
 
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  • #2
Originally posted by Mattius_
well i know I am wrong somewhere so show me where...

couldnt we calculate the size of the universe by taking the speed of light and the estimated age of the universe (14.5 billion years) and consequently use 14.5 billion light-years as a radius and put it into the old spherical volume equation (4/3 * pi * r3)


You're not wrong at all. This is considered to be the size of the universe.

Some dispute it. Mainly those (idiots) who claim the BB never occured. And then I think there are some rash BB proponents that define it from other terms.

But yes you are correct. Light did emit from the big bang within the first 1/2 second which has been proven. And light has presumably always traveled at C - thus you got it bud...!
 
  • #3
Greetings !
Originally posted by Mattius_
well i know I am wrong somewhere so show me where...

couldnt we calculate the size of the universe by taking the speed of light and the estimated age of the universe (14.5 billion years) and consequently use 14.5 billion light-years as a radius and put it into the old spherical volume equation (4/3 * pi * r3)
No. You assume that the Universal expansion occurs at the speed
of light, and that is not the case at all.

Live long and prosper.
 
  • #4
well we have proven that light was emitted, where has the resistance been?? on the other side of the universe??

if light speed was reached, it should be maintained to this day unless some sort of resistance has been limiting light speed.
 
  • #5


Originally posted by drag
Greetings !

No. You assume that the Universal expansion occurs at the speed
of light, and that is not the case at all.

Live long and prosper.


Drag - You completely and totally misunderstood this.

He DID NOT assume the universal expansion occurs at the speed of light.

Light was emited from the big bang initially. And since nothing travels as fast as light - the light continues to be the furthest from the big bang origin.

So you are wrong.
 
  • #6


Originally posted by CrystalStudios
Drag - You completely and totally misunderstood this.

He DID NOT assume the universal expansion occurs at the speed of light.

Light was emited from the big bang initially. And since nothing travels as fast as light - the light continues to be the furthest from the big bang origin.

So you are wrong.
No. As the Universe expands the light gets streched out on
the "surface" of space-time that in turn expands faster than c.

Live long and prosper.
 
  • #7
Originally posted by Mattius_
well we have proven that light was emitted, where has the resistance been?? on the other side of the universe??

if light speed was reached, it should be maintained to this day unless some sort of resistance has been limiting light speed.
What "resistence" ? To what ? What do you mean by "light speed
was reached" ? Please explain.
 
  • #8
Originally posted by Mattius_
well i know I am wrong somewhere so show me where...

couldnt we calculate the size of the universe by taking the speed of light and the estimated age of the universe (14.5 billion years) and consequently use 14.5 billion light-years as a radius and put it into the old spherical volume equation (4/3 * pi * r3)

You or anybody can say it is whatever you want. Why not at least find out what the professionals say? Your tax money supports them.

Lineweaver's easy-reading summary of current cosmology is online at Caltech or downloadable from the arxiv. I posted the link in Astronomy forum. It is in line with latest data and he is a top cosmologist.

the universe is most likely infinite
the current radius of the observable universe----the ball containing objects whose light has reached us---is 47 billion lightyears

it is bigger than you might expect because space has expanded since those objects emitted the light that is now reaching us

Lineweaver also gives a figure for the distance to the cosmological horizon or "event horizon"-----there is a larger ball containing objects whose light can be expected to reach us if we wait long enough and the radius is IIRC 62 billion lightyears.

this is on the basis of the standard picture of the universe, latest data etc.
You get the same general picture from e.g. Ned Wright's UCLA site, this is just a few months more up to date.
 
  • #9


Originally posted by drag
No. As the Universe expands the light gets streched out on
the "surface" of space-time that in turn expands faster than c.

Live long and prosper.


You are incorrect.

The matter of the universe did expand away from the now empty point of the BB. However it all expanded in a sphere away, and thus paved the way for the network of space.

Space exists currently in a complete sphere with the origin of the BB at the center.

Space does not exist on a curve of a sphere - but matter does.

So you are insanely wrong.
 
  • #10


Originally posted by CrystalStudios
You are incorrect.

The matter of the universe did expand away from the now empty point of the BB. However it all expanded in a sphere away, and thus paved the way for the network of space.

Space exists currently in a complete sphere with the origin of the BB at the center.

Space does not exist on a curve of a sphere - but matter does.

So you are insanely wrong.
O.K. What ever you say...
Maybe you should read marcus's post, I think he knows
a "bit" more than me and, surprisingly, even you...:wink:

Peace and long life.
 
  • #11
did anyone read that one book on varying speed of light? (VSL)? could throw my hypothesis out the window.
 
  • #12
drag is right in the sense that the area of the universe is increasing at a rate that would suggest it is moving faster than c, but what you fail to realize is that at no part on the edge of the universe is it moving greater than c. it is traveling at c but in both directions, thus increasing at 2c or greater(?).
 
  • #13
heh now my head hurts, thanks maximus...
 
  • #14
CrystalStudios, you are wrong on a couple of counts:

1) The idea that all of space expanded from a point has been discarded by Atronomers and Cosmologists for quite some time. It is now believe that expansion occurs at ever point in spacetime, and thus every point is the center of the Universe.

2) The Universe can indeed expand at a speed greater than c. General Relativity allows for this. I'll use the balloon analogy to explain it, but just remember that it is flawed in assuming that the Universe expanded from one point: Imagine that there is a balloon with little spots on it (the balloon symbolizing space and the spots representing matter), and there is a rule (a physical Law) that states that no spot can move away from another at a speed greater than 1 in./second. Now, if the balloon were to inflate (expand), then the space between two spots could indeed increase at a rate greater than 1 in./second, but the two spots wouldn't be "moving" at all, and so they are not breaking the rule.
 
  • #15


Originally posted by CrystalStudios So you are insanely wrong.
I'd say you are insanely wrong and drag is insanely right. Do try to understans what he and others are saying.
 
  • #16
so how the hell do we work out t he size of the universe, or can't we. cos I've just read all this and am insanely confused.
 
  • #17
As a simple analogy so I can understand Drag and some others:


Yes the "sphere" is expanding but so is the "space" inside the sphere? In other words:
1.) particles: photons, neutrons, atoms, sub atomic particles, etc... are indeed expanding like most of us agree.

But:

2.) the space that everything exists in is also expanding?


Finding the size of #1 can be done using math even I may be able to understand. How to you calculate the value of #2?
 
  • #18
1.) particles: photons, neutrons, atoms, sub atomic particles, etc... are indeed expanding like most of us agree.
Who agrees?
 
  • #19
It is my understanding that spacetime itself is expanding and this expansion is not limited by the c constant because the speed of light is constant and a limit only within the universe. Also there is a little thing called inflation. Inflation was the fastern than light expansion of the universe in the fist few billionth of a second and possibly again later and may satill begoing one as there is evidence that the expansion is accellerating and may be faster than the speed of light now. So to answer the original question of this thread. No.
That is not a valid way to measure the size of the universe.
 
  • #20
Originally posted by DR OF DEATH
so how the hell do we work out t he size of the universe, or can't we. cos I've just read all this and am insanely confused.
As someone else has mentioned, I don't believe the universe has a finite size. If it were finitely large, what would one find across the "borders"?

Originally posted by kauai_diver
Yes the "sphere" is expanding but so is the "space" inside the sphere? In other words:
1.) particles: photons, neutrons, atoms, sub atomic particles, etc... are indeed expanding like most of us agree.
Once again, I don't think that's right. Going with the balloon analogy, the dots on it are like points - they do not (and cannot) expand, only the distances between them do. In the same manner, galaxies (or particles) don't grow bigger with time, only the distances between them do. If particles were expanding, the distances wouldn't.
 
  • #21
Originally posted by Mattius_
well i know I am wrong somewhere so show me where...

couldnt we calculate the size of the universe by taking the speed of light and the estimated age of the universe (14.5 billion years) and consequently use 14.5 billion light-years as a radius and put it into the old spherical volume equation (4/3 * pi * r3)

this is not the size of the whole universe, this is the size of the current hubble volume which is defined as all the points which are causally connected to us. since the universe might be infinite, this has little bearing on the actual size of the universe, but is still a useful concept for some purposes
 
  • #22
Originally posted by Mattius_
well i know I am wrong somewhere so show me where...

couldnt we calculate the size of the universe by taking the speed of light and the estimated age of the universe (14.5 billion years) and consequently use 14.5 billion light-years as a radius and put it into the old spherical volume equation (4/3 * pi * r3)
All you can really measure is the "size" of the universe that is currently visible to us, i.e the part of the universe that has emitted light that had enough time to reach us.

Also, since light-years measure distance, what unit would be used to describe the result of this (hypothetical) calculation?
 
Last edited:

Question 1: How do scientists calculate the size of the universe?

Scientists use a variety of methods to estimate the size of the universe, including measuring the distance between celestial objects, studying the cosmic microwave background radiation, and utilizing mathematical models.

Question 2: What is the current estimated size of the observable universe?

The current estimated size of the observable universe is about 93 billion light years in diameter. However, the actual size of the entire universe may be much larger and is still unknown.

Question 3: Can we measure the size of the universe accurately?

Due to the vastness and complexities of the universe, it is impossible to measure its size with 100% accuracy. However, scientists continue to refine their methods and technology to improve the accuracy of their calculations.

Question 4: Does the size of the universe change over time?

The size of the universe is constantly changing due to the expansion of space. This expansion is believed to have started with the Big Bang and continues to this day.

Question 5: How does the size of the universe compare to other known objects?

The size of the universe is incomprehensibly larger than any known object in the universe. For example, the size of the observable universe is about 10^23 times larger than the Earth's diameter.

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