# Thread: what is the weight of universe?

1. I was reading about weight of planets and sun and moon. this question came into my mind

At time of big bang temperature was infinite, time was zero, density was infinite. What was the weight and what was the mass at that time?
In present time weight of a body keeps on changing, but mass remains same. (example: moving to moon will change the weight but not mass.) why weight does not remain same? what was the reaction at the ime of BB that caused/effected this difference?

And does space possess weight? (Space: empty space between and within galaxies ,through which light travels at speed of 186000miles per second).

2.

3. And if we know mass of a body, can we calculate its weight? or
And if we know weight of a body, can we calculate its mass?

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If you don't believe me, weigh it yourself.

5. The universe weighs nothing.

6. Originally Posted by sir ir r aj
And if we know mass of a body, can we calculate its weight? or
And if we know weight of a body, can we calculate its mass?
2x Yes. Weight is the force (caused by gravity), which acts on a body with some mass and (hopefully) gives it some acceleration.
According to second Newton's law:
Force is equal to mass times acceleration.

We can denote weight as W (or in my country G) and take acceleration as gravitational acceleration (g).
this is an equation showing the relation of weight to mass.

However, acceleration is relative. We can take into account only acceleration due to the "weight" force, which might be a little complicated in the example of universe.

7. The Universe 2 decades ago would have said to be weightless. Now with unexplained acceleration of expansion and the increasing acceptance of multi universe theory, it could have 'weight'.

8. Depends. What's the gravity of the universe?

9. Well in my opinion (with my quite limited knowledge of physics), the weight is a gravitational force of some system on another system... so if we take system #1 as universe... we don't have the other system to compare with, because universe is "everything" so it makes no sense to talk about the weight of the universe. (taking into account newton's law, because gravitational acceleration caused by non-existent gravitational field of nothing is 0, therefore weight of universe compared to nothing =0, QED. Dywyddyr is right)

We could talk about mass of the universe, which would be sum of all partial masses of all particles in the universe... (I'm not gonna calculate this, my computer would perform my autodafé)

or if we somehow could calculate the energy and "speed" of the universe, we could use:

10. What is the actual color of universe?

11. Is it possible to through earth out of universe. maybe into another universe, if there is?

12. Originally Posted by sir ir r aj
What is the actual color of universe?
Definitely blue. Light-ish one with a subtle green tone.

It's like.. what color is the Earth? There are all the colors.
BUT.. there are more of some colors than others!

Really the answer is so close to white, it is difficult to say.

Source

13. Article has really dealt with this topic thoroughly
So what is the average color? i.e. the color an observer would see if they had the Universe in a box, and could see all the light at once (and it wasn't moving, for a real observer on earth, the further away a galaxy from us the more it is redshifted. We have de-redshifted all our light before combining).

The universe started out young and blue, and grew gradually redder as the population of evolved 'red' giant stars built up. The rate of formation of new stars has declined precipitously in the last 6 billion years due to the decline in reserves of interstellar gas for forming new stars. As the star-formation rate continues to decline and more stars become red giants the color of the Universe will become redder and redder. Eventually all stars will disappear and nothing will be left but black holes. These too will eventually evaporate via the Hawking process and nothing will be left except for old light, which will itself redden as the Universe expands forever (in the current cosmological model).

thanks for this article. Should we not go out of universe to actually observe how our universe look like at thi time? I mean , no matter which color your paint is in a jar it will be black untill jar is opened.

14. Well. even if you did get out of the universe (which I can't imagine), the color which you would see at the "end" of the universe would be "older" and different than the color which you'd see at the nearest point of it. How would you know that you're finally out of the universe? Wouldn't your presence "outside" of the universe actually expand the universe, making you again inside? There are too many technical problems for me. Maybe someone more educated here will resolve it for you.

I think even inside universe, we can make an educated guess.

15. My ex-girlfriend's ass accounts for half of it.

16. Originally Posted by MacGyver1968
My ex-girlfriend's ass accounts for half of it.
Don't tell me, your new girlfriend's ass accounts for the other half

17. Originally Posted by sir ir r aj
What is the actual color of universe?
Depends. What color is a red apple under a blue light?

18. Originally Posted by MacGyver1968
My ex-girlfriend's ass accounts for half of it.
Insert "Moons of Uranus joke" here.

19. MODERATOR NOTE : I am moving this to "New Hypothesis" for now. To be honest, I am not quite sure where this really belongs.

20. Originally Posted by Dywyddyr
The universe weighs nothing.
Why?

21. Originally Posted by The Huntsman
Why?
Weight is the force that a mass experiences in an external gravitational field; since there is no "outside" to the universe, the notion of weight is not defined for it. It might however be possible to attribute a total mass to the universe, at least if it is closed and finite. Mass and weight are not the same.

22. Originally Posted by PhDemon
As mass and energy are equivelant if the total energy is zero you can say the total mass is zero(?) - not sure if this is technically correct though.
I'm afraid things aren't that simple - the traditional E=mc^2 formula is true only in locally inertial frames. If we want to consider the universe as a whole, its total mass would be the (0,0) component of the energy-momentum tensor integrated over all of space-time :

This isn't zero, since this component is always positive or zero, even if the universe has zero total energy. The question is rather whether or not this integral is finite - this will depend on the geometry and topology of the universe.

23. Originally Posted by Markus Hanke
Originally Posted by The Huntsman
Why?
Weight is the force that a mass experiences in an external gravitational field; since there is no "outside" to the universe, the notion of weight is not defined for it. It might however be possible to attribute a total mass to the universe, at least if it is closed and finite. Mass and weight are not the same.
So would weight be dependent on the strength of gravity? How would you weigh something without gravity? Like how would you get the mass of the universe, but not the weight?

24. Originally Posted by The Huntsman
So would weight be dependent on the strength of gravity?
Absolutely. You weigh more on earth than on the moon (by about a 6:1 ratio -- see footage of Apollo astronauts).

How would you weigh something without gravity? Like how would you get the mass of the universe, but not the weight?
Since weight is gravity-dependent, it only has meaning if the gravitational conditions are specified.

As to the mass of the universe, Markus provided the formal definition. At the present time, we do not know enough to complete the integration to yield a number.

25. Originally Posted by The Huntsman
So would weight be dependent on the strength of gravity? How would you weigh something without gravity? Like how would you get the mass of the universe, but not the weight?
Yes.

Originally Posted by Flick Montana
Depends. What's the gravity of the universe?

26. Originally Posted by tk421
Originally Posted by The Huntsman
So would weight be dependent on the strength of gravity?
Absolutely. You weigh more on earth than on the moon (by about a 6:1 ratio -- see footage of Apollo astronauts).

How would you weigh something without gravity? Like how would you get the mass of the universe, but not the weight?
Since weight is gravity-dependent, it only has meaning if the gravitational conditions are specified.

As to the mass of the universe, Markus provided the formal definition. At the present time, we do not know enough to complete the integration to yield a number.
Interesting. Is it possible to weigh everything in the universe using the earths gravity as a standard measuring unit? I guess that way us as humans would be able to relate to it.. although it would probably also be a complete waste of time as it wouldn't mean anything.

27. Originally Posted by The Huntsman
Originally Posted by tk421
Originally Posted by The Huntsman
So would weight be dependent on the strength of gravity?
Absolutely. You weigh more on earth than on the moon (by about a 6:1 ratio -- see footage of Apollo astronauts).

How would you weigh something without gravity? Like how would you get the mass of the universe, but not the weight?
Since weight is gravity-dependent, it only has meaning if the gravitational conditions are specified.

As to the mass of the universe, Markus provided the formal definition. At the present time, we do not know enough to complete the integration to yield a number.
Interesting. Is it possible to weigh everything in the universe using the earths gravity as a standard measuring unit? I guess that way us as humans would be able to relate to it.. although it would probably also be a complete waste of time as it wouldn't mean anything.
Regrettably, to do what you propose actually requires determining the mass of the universe. From the mass, one can compute the weight in any gravitational environment you select (if you want to compute your weight on other worlds, see Your Weight on Other Worlds | Exploratorium). But since we don't know the mass of the universe, we're stuck.

28. Originally Posted by Flick Montana
Originally Posted by sir ir r aj
What is the actual color of universe?
Depends. What color is a red apple under a blue light?
black?

29. Originally Posted by sir ir r aj
Originally Posted by Flick Montana
Originally Posted by sir ir r aj
What is the actual color of universe?
Depends. What color is a red apple under a blue light?
black?
And black is the absence of colour...

I've read colour is our brains virtual interpretation of light waves absorbed by our eyes. Your brains interpretation of light may differ slightly to my brains interpretation of light.

In other words, colour is no more real than that pink penguin I just made you think about right now.

30. From what I've heard, even the language you learned your color names from has a significant effect on your ability to perceive colors. In languages that don't separate what we'd call blue from what we'd call green, the people that grew up with that language don't see the two as distinct colors. Makes you wonder a bit about what colors we might be missing out on.

31. Originally Posted by MacGyver1968
My ex-girlfriend's ass accounts for half of it.
The mass of the ass is inversely proportional to the angle of the dangle times the heat of the meat . Not to be confused with the ratio of fellatio or the power of deflower.

32. It weighs approximately √-1 Plancks.

33. Originally Posted by zinjanthropos
The mass of the ass is inversely proportional to the angle of the dangle times the heat of the meat . Not to be confused with the ratio of fellatio or the power of deflower.
This clearly calls for the hardcore edition...

34. Markus if you were able to count all the atoms in the universe would getting the mass be possible?

35. Originally Posted by The Huntsman
Markus if you were able to count all the atoms in the universe would getting the mass be possible?
In principle yes. If you know the number of atoms and a rough breakdown of which elements are involved, you can calculate the total mass - provided, of course, that the number of atoms is finite.

36. Originally Posted by Markus Hanke
Originally Posted by The Huntsman
Markus if you were able to count all the atoms in the universe would getting the mass be possible?
In principle yes. If you know the number of atoms and a rough breakdown of which elements are involved, you can calculate the total mass - provided, of course, that the number of atoms is finite.
Cool. As the universe expands, is it actually gaining atoms or just stretching out the ones already there?

37. Originally Posted by The Huntsman
Cool. As the universe expands, is it actually gaining atoms or just stretching out the ones already there?
Metric expansion "stretches out" space in between gravitationally bound systems, for example in the largely empty void between galaxies and clusters and such. It doesn't have a net effect on anything that is held together by gravity, for example our solar system, or atoms. The other thing that needs to be remembered is that metric expansion is such a small effect that it becomes relevant only on very large scales, such as galaxy clusters; it then is a cumulative effect in that the more space is between us and a distant object, the more expansion is seen.

No matter is created during expansion, so the answer to that bit is no.

38. Originally Posted by Markus Hanke
Originally Posted by The Huntsman
Cool. As the universe expands, is it actually gaining atoms or just stretching out the ones already there?
Metric expansion "stretches out" space in between gravitationally bound systems, for example in the largely empty void between galaxies and clusters and such. It doesn't have a net effect on anything that is held together by gravity, for example our solar system, or atoms. The other thing that needs to be remembered is that metric expansion is such a small effect that it becomes relevant only on very large scales, such as galaxy clusters; it then is a cumulative effect in that the more space is between us and a distant object, the more expansion is seen.

No matter is created during expansion, so the answer to that bit is no.

ahhhhhhhh so as expansion continues, the void gets bigger, the 'negative pressure' gets stronger which attributes to the 'accelerating expansion' of the universe as being exponential?

39. Originally Posted by The Huntsman
ahhhhhhhh so as expansion continues, the void gets bigger, the 'negative pressure' gets stronger which attributes to the 'accelerating expansion' of the universe as being exponential?
Yes, precisely. And since space stretches out between ourselves and the object, it looks to us like the object recedes very very rapidly, even though it is in effect nearly stationary. What we are seeing is the effect of metric expansion.

40. Originally Posted by Markus Hanke
Originally Posted by The Huntsman
ahhhhhhhh so as expansion continues, the void gets bigger, the 'negative pressure' gets stronger which attributes to the 'accelerating expansion' of the universe as being exponential?
Yes, precisely. And since space stretches out between ourselves and the object, it looks to us like the object recedes very very rapidly, even though it is in effect nearly stationary. What we are seeing is the effect of metric expansion.
That means temerature is increasing which cause expansion? (2.7 K ) Has Temperature not decreased since BB?
If we calculate weight of universe will it help us to find escape velocity for universe?

41. Originally Posted by Markus Hanke
Originally Posted by The Huntsman
ahhhhhhhh so as expansion continues, the void gets bigger, the 'negative pressure' gets stronger which attributes to the 'accelerating expansion' of the universe as being exponential?
Yes, precisely. And since space stretches out between ourselves and the object, it looks to us like the object recedes very very rapidly, even though it is in effect nearly stationary. What we are seeing is the effect of metric expansion.
I had a look at 'metric expansion' on Wikipedia and I must admit, it is extremely difficult to imagine just what is going on with it. I just can't see how something can be moving away, but when you measure it they are the same distance apart.

42. Originally Posted by The Huntsman
I had a look at 'metric expansion' on Wikipedia and I must admit, it is extremely difficult to imagine just what is going on with it. I just can't see how something can be moving away, but when you measure it they are the same distance apart.
I think you misunderstood that. The proper distance does not remain the same, it does indeed increase, as is stated in the very first sentence of that article you are referring to - that's the whole idea of metric expansion. You can roughly picture it as a balloon that is being blown up - the more air you blow into it, the more it expands, and the further apart any two points on its surface become. The universe works in a similar way, only in 3 dimensions instead of 2.

I think what you might be referring to is the possibility of reparametrizing everything in terms of comoving coordinates - such as system of coordinates compensates for the metric expansion of space, so distances remain fixed by definition. I would advise that, in order to avoid any unnecessary confusion, to disregard comoving coordinates for the moment. Proper distances, as we would commonly measure them, do indeed increase due to metric expansion.

That means temerature is increasing which cause expansion? (2.7 K ) Has Temperature not decreased since BB?
Why would that mean that the temperature increases ? As the universe expands, the average energy density ( average energy per unit volume of space ) decreases, i.e. the CMBR cools.

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