Nor me, but I can supply the fascinating fact that a cubic light year (ly³) is a cube which is 6 trillion miles on each side.
Or, in everyday terms, a volume equivalent to the capacity of 1.7 x 10^53 teaspoons!
Attachments
It’s 317 x 317 x 317 light years. So you have 31 million cubic light years 👍Unless I am mistaken, I get 31,855,013 as the cube of 317.
I checked this two ways:
View attachment 1282413
View attachment 1282415
Happy with that. No idea what it means, of course.
Gravity is a subject I dislike. I fear heights. And so should YOU.
That being your calculated volume of the universe if it had a uniform density equal to that of water and was formed into a cube shape?
That's quite a squash compared to the volume of our (non-uniform density) observable universe which is around 4 x 10^32 cubic light years!
I was quite surprised. Maybe you or Steve should check my calculations - even ChatGPT got wrong twice in a row so I won’t feel aggrieved if wrong 😑
I just wanted to see what volume of all visible matter would be in relation to something I (or anyone else) was familiar with. For example, the average density of the sun (taking the photosphere as the outer limit) is about 1.4x that of water although the density at the core is 160 000kg/m^3.
I just wanted to see what volume of all visible matter would be in relation to something I (or anyone else) was familiar with. For example, the average density of the sun (taking the photosphere as the outer limit) is about 1.4x that of water although the density at the core is 160 000kg/m^3.
Let's take it from the top:
https://en.wikipedia.org/wiki/Fine-structure_constant
Just showin' off here.
https://en.wikipedia.org/wiki/Fine-structure_constant
Just showin' off here.
We discussed the fine structure constant at some length earlier in the thread.
The numerical values of constants which involve units of mass, length and time etc. depend on the units we use. The numbers would change if we used different units.
However, certain constants, like the fine structure constant, do not depend on the units we use. These are called "dimensionless" constants and they tell us facts about nature that are completely independent of our choices of units.
In short, the fine structure constant is one of the fundamental constants that describes the universe.
Galu, I know that, but the way folk go on about it, you'd think there was some witches' brew involved. Why does C travel at the velocity it does? Why is Newton's gravitational constant what it is?
About 5% or 0.05 of the universe is ordinary matter.
The critical density for the Universe is approximately 10^-26 kg/m^3.
The universe has total density close to critical density, hence ordinary matter density is 0.05 x 10^-26 = 5 x 10^-28 kg/m^3.
Now, the density of water is 10^3 kg/m^3 which is a factor of 5 x 10^31 denser. than the ordinary matter density.
If we approximate the universe as a cube where each of its 3 dimensions is 8.8 x 10^26 metres (93 billion light years), we would have to reduce each of these dimensions by a factor equal to the cube root of 5 x 10^31 which is 3.7 x 10^10.
So, the 'water universe' cube would have sides (8.8 x 10^26)/(3.7 x 10^10) = 2.4 x 10^16 m.
Thus, the 'water universe' would have a volume of (2.4 x 10^16)^3 = 1.4 x 10^49 cubic metres.
Since there are approximately 1.2 x 10^-48 cubic light years in a cubic metre, this equivalent volume is (1.4 x 10^49) x (1.2 x 10^-48) = 17 cubic light years.
The 'water universe' would therefore be a cube where each side is 2.6 light years in length.
N.B. All calculations rounded to two figures.
P.S. I based these calculations on material I found on the web. Be assured that, having spent too much time on this, I'll be exploring it no further. However, feel free to correct my premise and my calculations if you will!
The velocity of light is related to the fine structure constant.
Note also that the coupling factor of the electromagnetic force (1/137) is the same as the fine structure constant.
Fascinating!
So you disagree with me and with Chat GPT!About 5% or 0.05 of the universe is ordinary matter.
The critical density for the Universe is approximately 10^-26 kg/m^3.
The universe has total density close to critical density, hence ordinary matter density is 0.05 x 10^-26 = 5 x 10^-28 kg/m^3.
Now, the density of water is 10^3 kg/m^3 which is a factor of 5 x 10^31 denser. than the ordinary matter density.
If we approximate the universe as a cube where each of its 3 dimensions is 8.8 x 10^26 metres (93 billion light years), we would have to reduce each of these dimensions by a factor equal to the cube root of 5 x 10^31 which is 3.7 x 10^10.
So, the 'water universe' cube would have sides (8.8 x 10^26)/(3.7 x 10^10) = 2.4 x 10^16 m.
Thus, the 'water universe' would have a volume of (2.4 x 10^16)^3 = 1.4 x 10^49 cubic metres.
Since there are approximately 1.2 x 10^-48 cubic light years in a cubic metre, this equivalent volume is (1.4 x 10^49) x (1.2 x 10^-48) = 17 cubic light years.
The 'water universe' would therefore be a cube where each side is 2.6 light years in length.
N.B. All calculations rounded to two figures.
P.S. I based these calculations on material I found on the web. Be assured that, having spent too much time on this, I'll be exploring it no further. However, feel free to correct my premise and my calculations if you will!
That's modern physics for you!
It does seem that is a very compact water universe! So everything in the complete universe fits into a cube of 2.6 LY sides!
I tried Chat GBT again by restating the problem, and it seems there is a more sensible answer from it (not saying you are wrong Galu):-
You
if everything in the universe was packed into a cube with the density of water, how big would the cube be?
ChatGPT
To calculate the size of the cube, we would need to know the approximate total mass of the observable universe. The observable universe is estimated to have a mass of about (3 \times 10^{54}) kilograms.
Given that the density of water is about (1000 , \text{kg/m}^3), we can calculate the volume of the cube using the formula:
[ \text{Volume of cube} = \frac{\text{Total mass of universe}}{\text{Density of water}} ]
Then, we can find the side length of the cube by taking the cube root of the volume.
Let me calculate that for you.
After performing the calculations, the cube would have a side length of approximately (1.41 \times 10^{17}) meters or around 141 quadrillion meters. This is an incredibly large-scale size, highlighting the vastness of the universe.
You
can you regenerate your response but state the answer in light years?
ChatGPT
Converting the side length of the cube from meters to light years, we can use the conversion factor:
1 light year = (9.461 \times 10^{15}) meters
The side length of the cube, which is approximately (1.41 \times 10^{17}) meters, would be equivalent to:
[ \frac{1.41 \times 10^{17} \text{ meters}}{9.461 \times 10^{15} \text{ meters/light year}} \approx 14.9 \text{ light years} ]
Therefore, if the entire universe were packed into a cube with the density of water, it would result in a cube with a side length of roughly 14.9 light years. This enormous scale showcases the immense size and magnitude of the universe.
You
if everything in the universe was packed into a cube with the density of water, how big would the cube be?
ChatGPT
To calculate the size of the cube, we would need to know the approximate total mass of the observable universe. The observable universe is estimated to have a mass of about (3 \times 10^{54}) kilograms.
Given that the density of water is about (1000 , \text{kg/m}^3), we can calculate the volume of the cube using the formula:
[ \text{Volume of cube} = \frac{\text{Total mass of universe}}{\text{Density of water}} ]
Then, we can find the side length of the cube by taking the cube root of the volume.
Let me calculate that for you.
After performing the calculations, the cube would have a side length of approximately (1.41 \times 10^{17}) meters or around 141 quadrillion meters. This is an incredibly large-scale size, highlighting the vastness of the universe.
You
can you regenerate your response but state the answer in light years?
ChatGPT
Converting the side length of the cube from meters to light years, we can use the conversion factor:
1 light year = (9.461 \times 10^{15}) meters
The side length of the cube, which is approximately (1.41 \times 10^{17}) meters, would be equivalent to:
[ \frac{1.41 \times 10^{17} \text{ meters}}{9.461 \times 10^{15} \text{ meters/light year}} \approx 14.9 \text{ light years} ]
Therefore, if the entire universe were packed into a cube with the density of water, it would result in a cube with a side length of roughly 14.9 light years. This enormous scale showcases the immense size and magnitude of the universe.
Or as I like to say, 'We find ourselves where we are' so lets just get on with it!The velocity of light is related to the fine structure constant.
View attachment 1283103
Note also that the coupling factor of the electromagnetic force (1/137) is the same as the fine structure constant.
Fascinating!
I don’t understand the whole thing about trying to unify GR and QM. These were unified at the start of the universe just prior to and during and just after the inflationary epoch. At some point during the process, the various forces decoupled (called a ‘phase change’ by physicists) and we subsequently end up with the 4 forces we see now.
I listened to a pod cast by Lawrence Krauss talking to Richard Dawkins. The latest thinking about gravity is that bodies that are gravitationally bound, exchange ‘gravitons’.
There is as much confusion, outrageous ideas and downright fantasy in bleeding edge theoretical physics IMV as there is in every other walk of life. As he was talking, I imagined what Albert Einstein would be doing if he was sitting there in the studio with Krauss and Dawkins. He’d just have a smile on his face as he thought ‘oh dear’.
BTW Krauss didn’t seem entirely convinced about the whole graviton thing.
I listened to a pod cast by Lawrence Krauss talking to Richard Dawkins. The latest thinking about gravity is that bodies that are gravitationally bound, exchange ‘gravitons’.
There is as much confusion, outrageous ideas and downright fantasy in bleeding edge theoretical physics IMV as there is in every other walk of life. As he was talking, I imagined what Albert Einstein would be doing if he was sitting there in the studio with Krauss and Dawkins. He’d just have a smile on his face as he thought ‘oh dear’.
BTW Krauss didn’t seem entirely convinced about the whole graviton thing.
The graviton, which is thought to communicate the force of gravity, remains hypothetical.
Note the part of the above description that says "Some theorists believe gravitons can travel between braneworlds".
The hypothesis is that our 3D universe is restricted to a 'brane' which exists inside a higher dimensional space called the 'bulk' (or 'hyperspace').
It is postulated that the electromagnetic, weak and strong nuclear force are confined to the brane, while gravity leaks into the bulk.
As a consequence, the force of gravity should appear significantly stronger on small (subatomic or sub-millimetre) scales, where less gravitational force has leaked. https://en.wikipedia.org/wiki/Brane_cosmology
As we saw earlier, experiments are underway to test this supposition.