# Can you increase the mass of a closed system with information?

• I
• Pony
Pony
TL;DR Summary
There are several theorems and equations connecting information and energy/mass (I don't know any), I am interested putting information into a closed system.
Let's assume that there is a closed box, with mass M. There are some random quantum processes inside it, say radioactive decay. Let's assume that we can manipulate the decay from the outside somehow, thus 'putting information' into the box. Can that affect its mass?

Information is rather related to entropy than to mass. Where did you get this idea from?

Pony said:
andom quantum processes inside it.. can manipulate the decay from the outside
Which is it? Is it random? Or is it controlled?

Pony said:
TL;DR Summary: There are several theorems and equations connecting information and energy/mass (I don't know any), I am interested putting information into a closed system.

Let's assume that there is a closed box, with mass M. There are some random quantum processes inside it, say radioactive decay. Let's assume that we can manipulate the decay from the outside somehow, thus 'putting information' into the box. Can that affect its mass?
If information has mass or energy then you cannot put information into a closed box. So the question needs to be modified. If information has mass and if the box is closed to mass and energy transfer except for the information, then yes the information transfer would affect the mass of the box.

A direct link to the specific theorem or equation you are thinking of would be helpful.

vanhees71
Three replies, three different problems with the question found. Maybe the OP should think about what he is asking more carefully and try again - and yes, if the question is based on something he read somewhere, tell us and don't leave us to guess.

Pony, russ_watters, vanhees71 and 1 other person

Now I think that putting information into a closed box only can affect its entropy (thus, 'violating' the second law of thermodynamics), but not its mass/energy.

For example if we put down a box with low entropy, say there is gas in it, but it is concentrated in the left half of it, its entropy will (most likely) increase, the gas will spread in the box. This doesn't affect its mass. With a demon that we feed information from outside, we can make the gas concentrated in the left half of it again, that would not affect its mass. (Actually, we don't need a demon, we can just wait for it to happen.)

Pony said:
putting information into a closed box
How are you going to do this? You need to be specific. Just waving your hands and saying "putting information into a closed box" tells us nothing about what is actually happening, and if we don't know what is actually happening, we can't possibly tell what the laws of physics say about the scenario.

vanhees71
Pony said:
I think that putting information into a closed box only can affect its entropy (thus, 'violating' the second law of thermodynamics), but not its mass/energy
What about those theorems that you mentioned above?

vanhees71
Pony said:
if we put down a box with low entropy, say there is gas in it, but it is concentrated in the left half of it, its entropy will (most likely) increase, the gas will spread in the box. This doesn't affect its mass.
In this scenario, no information is being put into the box from outside. So even if your description is correct, it's irrelevant to the question you are asking in the OP.

Pony said:
With a demon that we feed information from outside, we can make the gas concentrated in the left half of it again, that would not affect its mass. (Actually, we don't need a demon, we can just wait for it to happen.)
If you don't need the demon, then again this involves no information being put into the box from outside, so it's again irrelevant to the question you are asking in your OP.

The case with the demon could be relevant, but then the obvious next question is whether your claim, that the demon could do what you describe without affecting the mass of the gas, is correct. But work has to be done on the gas to concentrate it all in the left half of the box, and this work is a change in the total energy of the box and hence in its mass. The demon can't magically concentrate the gas by avoiding this requirement.

vanhees71
Frabjous said:
This paper is talking about storing information as bits in information storage devices. The concept of "information" that the OP of this thread is using is more general than that. For example, in the scenario of concentrating a gas entirely at one side of a box, there is no "information storage" as bits being done, but entropy is clearly changing, and work is clearly being done.

vanhees71
PeterDonis said:
This paper is talking about storing information as bits in information storage devices. The concept of "information" that the OP of this thread is using is more general than that. For example, in the scenario of concentrating a gas entirely at one side of a box, there is no "information storage" as bits being done, but entropy is clearly changing, and work is clearly being done.
I've not read the paper yet, but indeed to store information you always need some energy. E.g., to realize a (q)bit you can use a spin, and to change the spin to store information you need some energy. In this sense there's always some energy exchange between the qbit and the environment needed to store information.

I would question whether you are putting "information" into the box. Say it is a single radioactive atom with a long half-life. If you stimulated it's decay, you have information about a previously unknown decay-or-not. The information is not stored in the box.

Anyone coming along and seeing later if the atom is decayed, as a message has no way of knowing if the atom spontaneously decayed or was stimulated. I don't see how information was added to the box with that atom.

And as others have noted, the manipulation required something that has to be accounted for.

Put another way, if the thing in the box could change randomly, or by manipulation, that is not an information storage process. If decayed is a "1" and undecayed is a "0" then "1" can be the result of time or manipulation.

EDIT: Although, with your proposal ... you've made Schroedinger's cat very worried

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