Wikipedia:Reference desk/Archives/Science/2022 June 24

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

June 24

Is it at least theoretically possible to turn CO2 into fuel?

Could we, at least in theory, capture the CO2 of a running internal combustion engine and turn it back into some sort of fuel? Obviously, I see that you'll have to add energy to process CO2 back to fuel, but is the idea as crazy as time travel or simply in the ballpark difficulty of fusion energy or Mars travels? --Bumptump (talk) 12:04, 24 June 2022 (UTC)

It's similar to why you cannot have perpetual motion energy generators: C + O₂ -> CO₂ + energy; in order to reverse the reaction CO₂ + energy -> C + O₂, you would have to give it back the energy you got from it in the first place. Hence, no energy is left over, and because nothing is 100% efficient, you would lose energy overall. -- Verbarson  ^talk_edits 12:12, 24 June 2022 (UTC)

• That's why I said: " Obviously, I see that you'll have to add energy to process" The idea is to use it as a sort of battery. --Bumptump (talk) 17:07, 24 June 2022 (UTC)

See Carbon capture and utilization for how it is done. Graeme Bartlett (talk) 12:26, 24 June 2022 (UTC)

Some researchers are hyping this up as a serious prospect, see this website. To be practical, you would need some very inexpensive energy source to drive the process. Mike Turnbull (talk) 17:22, 24 June 2022 (UTC)

It can be done. Capturing the CO₂ from a running internal combustion engine is a bit hard (you use an ICE because you have some mobile application; CO₂ is a gas and hard to store on such an application), but you can blow the CO₂ into the air and capture it later. That's even less efficient, but if this captured CO₂ is the only viable or legal source of hydrocarbon fuel and hydrocarbon fuel is still the only technically viable aviation fuel, it will happen. Renewable electricity is very cheap at peak production times. The price often goes negative these days. You can build an electrolyser next to your wind/solar farm to avoid having to sell the electricity at a negative price; you only switch it on at peak production times. PiusImpavidus (talk) 18:23, 24 June 2022 (UTC)

You can do this by replacing the combustion engine with a horse that eats grass and pulls your wagon. But you have to accept a big reduction in your energy usage. If you want to use a combustion engine and an artificial process to turn the CO₂ back into fuel, that is also possible, but you'll still have to accept a much lower energy usage than what we're accustomed to. To go with the battery analogy, all the petroleum in the ground is an enormous battery that has been slowly charged up over a very long time, and we are currently discharging it very, very quickly. We can recharge it, but we don't have a way to recharge it as quickly as we're draining it now. --Amble (talk) 19:03, 24 June 2022 (UTC)

Well, carbon fusion and oxygen fusion both exist, in the cores of massive stars late in life, so yes, "at least in theory" you can use CO₂ as fuel. --Trovatore (talk) 19:46, 24 June 2022 (UTC)

Request for the research and thesis suggestions

Hello, I hope this is good place to ask this question as well. As a student doing masters in geoinformatics I will try to do thesis in crop remote sensing. I am doing another masters in agronomy (other being online) , what thesis area in agronomy will complement me later? Will it be appropriate if I choose precision agriculture in the agronomy thesis. I have general ideas what to be done. I was requesting how both thesis later in overall suits each other developing me as a more fluent in two domains.

I am not from other developed nations, there would probably have been graduate and career advisors. In my case, there are none, so I genuinely wanted some suggestions. If anyone wishes to suggest more, personal advice, there is email associated with the account. Any kind comments are welcomed. Even if none, thankyou. - Learnerktm 12:31, 24 June 2022 (UTC)

The central issues in the areas of remote sensing in geoinformatics are quite distinct from those of precision agriculture, so it seems to me that the domains are largely complementary. Since remote crop sensing can certainly find use in precision agriculture (check this out), it seems to me that the combined mastery of both can prove a valuable asset.  --Lambiam 22:49, 24 June 2022 (UTC)

Thankyou Lambiam for your kind comments,

not just in precision agriculture, do you have other kind suggestions that would suit each other? Learnerktm 11:03, 25 June 2022 (UTC)

Not exactly career advice, but I feel that while writing a Master's Thesis requires getting deep into a subject, it pays off in the end to keep a broad interest while pursuing the things you believe to be of interest, not what others tell you to be interested in. Some people can develop theory, pushing its boundaries, which is very valuable. Other people can use theory to create methods that are applied in practice, and that is equally valuable. What should you aim at? Find out where your passion is, and follow your passion – that is the best way to make a difference.  --Lambiam 20:56, 25 June 2022 (UTC)

Really thankyou for the nice advice. I will keep this in mind. :) Learnerktm 21:41, 25 June 2022 (UTC)

Does E=MC^2 violate conservation of energy?

This has always confused me. The first law of thermodynamics says that energy cannot be created or destroyed. But E=MC^2 says that energy can be created from mass. Assuming my understanding is correct, I've never heard anyone explicitly state that energy cannot be created or destroyed except for general relativity. A Quest For Knowledge (talk) 20:01, 24 June 2022 (UTC)

It is not created from mass. It just always exists. Ruslik_Zero 20:09, 24 June 2022 (UTC)

Conservation of Energy explains this, albeit with a lack of decent citations. Classical physics says energy is conserved and mass is conserved. Relativistic physics (probably there's a more accurate term) says mass-energy is conserved. --Floquenbeam (talk) 20:11, 24 June 2022 (UTC)

Indeed, in classical (Newtonian) physics we say mass is conserved and energy in conserved. In special relativity, we say that mass-energy is conserved, i.e., mass–energy conversion can occur just as one form of energy can be converted into another (e.g., gravitational potential energy into kinetic energy), but the total mass–energy of a closed system must be conserved and thus $E=mc^{2}$ does not violate the conservation law. ComplexRational (talk) 20:21, 24 June 2022 (UTC)

The obvious way of solving the apparent contradiction is to consider mass as a form of energy.^[1]  --Lambiam 22:57, 24 June 2022 (UTC)

Individual photons do not have an invariant mass and are therefore massless and only carry an energy in accord with the relativistic Doppler effect. That said, in general, mass and energy are equivalent per mass-energy equivalence and neither are created or destroyed. See center-of-momentum frame. If the COM frame exists for a system or body of particles, the system has a total energy and an equivalent invariant rest mass. Moreover, the equivalency holds whether or not particles are stable or undergo fission, fusion, or creation/annihilation. Even a system of photons, such as the gamma rays emitted after an antimatter-matter annihilation event may have a COM frame thus invariant mass. Modocc (talk) 01:40, 25 June 2022 (UTC)

COM frame always exists. Ruslik_Zero 20:05, 25 June 2022 (UTC)

From our article on center-of-momentum frame: "Systems that have nonzero energy but zero rest mass (such as photons moving in a single direction, or equivalently, plane electromagnetic waves) do not have COM frames, because there is no frame in which they have zero net momentum." Modocc (talk) 21:54, 25 June 2022 (UTC)

Ok, for a system with a non-zero invariant mass it always exists. Ruslik_Zero 12:17, 26 June 2022 (UTC)