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What matter Cannot be destroyed?

Energy Neither Created nor Destroyed

This is one of the most important rules that scientists have found which describes natural phenomena. Unfortunately there is no non-circular proof of energy conservation — in the end, all laws of physics that we know of are the result of observation, formation of hypotheses, making predictions, and testing them. Conservation of energy is one such law. If energy could be created or destroyed, all of our ideas of how the world works would have to be modified in some way (and we’d learn something very perplexing). But so far, energy seems not to be created or destroyed.

Energy can be converted from one form to another, though. Mechanical energy, such as the kinetic energy of motion, can be converted to heat energy, for example in the heating of a car’s brakes when it slows down. Chemical energy in the gasoline of the car can be converted into both heat energy in the exhaust and heating the engine, and into mechanical energy to move the car. Potential energy, such as the gravitational potential energy stored in an object which is on a high shelf, can be converted into kinetic energy as the object falls down. Electrical energy can be converted to heat or mechanical energy or sound energy in a variety of useful ways around the house using common appliances.

It is often the conversion of one form of energy to another which is the most important application of this rule. Often predictions of the behavior of physical systems are very much more easily made when using the idea that the total amount of energy remains constant. And careful measurements of different kinds of energy before and after a transformation always show that the total always adds up to the same amount.

Historically, of course not all the forms of energy were known to begin with. Scientists had to keep inventing more forms to keep the law of energy conservation true. If that process had gotten too messy or complicated to make sense, we would have had to give up the law.

One very interesting feature of energy is that other forms can be converted into rest mass and back again (particle physicists do this every day in their accelerators). Einstein’s E=mc^2 gives the relationship between the rest mass of a particle (measured in standard mass units) and the amount of energy that corresponds to (measured in standard energy units). It even applies to other systems where particles are neither created nor destroyed. If a box contains some air at a temperature, and then is warmed up, it will become ever so slightly more massive because of the extra energy given to it. You can call that rest mass of the whole box or the mass equivalent of the kinetic energy of the particles in it- nature doesn’t care what names you give it.

(published on 10/22/2006)

Follow-Up #1: mass-energy

Wouldn’t antimatter and natural matter annihilation be creating energy from mass?
— Jay Berkovitz (age 22)
Gushikawa, Okinawa, Japan

That depends on how you use the words. The thing which is conserved is the total energy including all the rest-energies of the particles. It’s that total «E» which is related to the «m» which is the source of gravity by E=mc 2 . So one way of viewing that annihilation is that it is converting the rest-mass form of energy into other forms. That’s the way we think when we say that the law of conservation of energy works.

(published on 10/22/2007)

Follow-Up #2: Loss of our energy while working

i wanna ask that when we work we losse our energy how?where does it go?
— bhawna (age 17)

When we do physical work, for example lifting up a bucket of water, we utilize the chemical energy in our body. This energy is supplied by the food we eat and is used up in a variety of ways: transfer of potential energy to the bucket of water, kinetic energy of a thrown ball, etc.
A large fraction of the food energy is used up in heating of our bodies. Nevertheless, adding it all up. Energy in = Energy out. Total energy is conserved.

(published on 10/22/2007)

Follow-Up #3: in the beginning

I would like to ask what your theory is on the beginning of energy. Where did it come from? There is the theory of God, but are there any other legitimate theories?
— Emily (age 13)
Southern Georgia, United States

Perhaps your question is really about the beginning of there being anything at all. The beginning of » energy» itself may not be quite the issue, because at least in some pictures of the universe (simple closed geometry) the total energy is and always was zero.

Our standard pictures can trace things back from now to a tiny fraction of a second after some dramatic ‘origin’ event. That may be the sort of inflationary Big Bang most often discussed or a collision between two 3-D ‘branes’ in a higher dimensional space. The consequences of those pictures for our current world would be only a bit different, so sorting out which picture is better isn’t done yet.
But you’re really asking about what got things started ‘before’ that. We don’t know if the idea of ‘before’ makes sense here, because in the mathematics describing this phase, there may be nothing like time which can be smoothly traced all the way through. Still, we can take the question as being «how does the universe fit into some bigger mathematical picture that all hangs together?» In other words, is there some big picture of spacetime in which the ‘beginning’ of our universe obeys the most basic laws, instead of just coming from nowhere?
We don’t know the answer to that yet, because we don’t yet know the most basic laws. String theorists and others are trying to work on those laws, but until they make more progress we won’t be able to say much about the very beginning of how our universe got started. You’re young though, so you may well live to see real progress on these questions.

(published on 12/18/2007)

Follow-Up #4: light energy

If energy cannot be created nor destroyed then where does the energy «physically» go after it is used? Example: I turn on a lamp. The light bulb in the lamp uses electricity (energy) to light a room. In order to keep the light shining I must ensure the on/off switch is «on» in order for the energy to be drawn from the electric socket into the light bulb. So — where does the energy «physically» go after it has been drawn from the socket and after it has lighted the bulb? Does it go into the air? How is the energy physically «recovered» after it has lighted the lamp if energy cannot be destroyed?
— Janice
Los Angeles CA, USA

The light energy gets converted to thermal forms- mainly jiggling of molecules- when it is absorbed by walls, rugs, etc. Of course you can sense that directly by how your hand warms up when light shines on it. Also, the bulb converts a lot of the electrical energy directly to thermal forms, so the bulb and the surrounding air heat up. The big advantage of compact fluorescent bulbs is that they send a much higher fraction of the input energy out as light than do incandescent bulbs.

(published on 09/17/2008)

Follow-Up #5: how does a room cool?

Ok, but then where does the heat energy go after the lamp is turned off and the room cools?
— Neil (age 38)

There are lots of ways that heat can leak out of a room. Maybe you have the windows open and the warmer air just blows out. Maybe it’s sealed up, and the heat leaks out by conduction, the gradual transmission of energy via thermal jiggles from one part of a material to the next.

(published on 09/11/2012)

Follow-Up #6: where does energy go?

It seems as if kinetic, sound, and potential energy all terminate. When pottery falls off of a shelf, there is no more potential energy, and after time and space sound is no longer detectable (right)? With kinetic energy, you throw a ball, and the energy of that system may be enough to change the shape of soil (causing an indent), but when the ball lands and physical changes are complete, the energy is destroyed, right? Where does it go when the «work» is complete in these examples?
— Carl (age 26)
Seward, AK, US

In all those cases, it goes into the thermal jiggling of atoms, molecules and electrons. Then it gets radiated as mainly infrared light out into space.

(published on 02/21/2013)

Follow-Up #7: source of car energy

I understand that energy can’t be created or destroyed but with a car, how does it just start? Where is the energy needed to power a car when it is stationary? Also what do you mean by the jiggling of atoms? Thanks
— William Duncan (age 17)
Adelaide, South Australia

In a typical car, the initial starting energy is stored in a battery. The chemicals in the charged-up battery are not in their lowest free-energy state. Then once the motor starts, the energy comes from combining the fuel with oxygen, which also lowers the chemical free-energy.

By atoms jiggling we just mean that they move around, with some kinetic energy. They also squash into each other as they jiggle, and that raises their potential energy. Just picture a bunch of little balls connected by springs, rattling around.

(published on 11/19/2013)

Follow-Up #8: energy conservation in the universe

Does the conservation of energy apply to the entire universe? That would mean that if the universe is expanding its energy density must be decreasing?
— Andy Findlay (age 52)

We’ve addressed the question of cosmological energy conservation in the expanding universe in other threads, e.g.: . The quick summary is that it’s over our heads.

At a more local level, however, it is quite true that as the universe expands the energy density goes down. It’s very similar to the adiabatic expansion of a gas. The densities of massive particles and of photons go down. The wavelengths of the photons stretch out, so there’s less energy per photon. The stretching of the photons means that there’s not only a lower energy density, but also lower absolute energy within the region that some collection of photons occupy. That all looks quite a bit like the classical expansion. One difference is that classically the lost energy goes into pushing on the walls, doing work on things outside. Cosmologically, there aren’t any walls, so this is trickier. Another issue is that there is some dark energy, or an effect that acts like dark energy, for which the energy density doesn’t change as the space expands. This dark energy is not currently well understood.

(published on 01/05/2016)

Follow-Up #9: relativistic energy

Hi Mike,In relativistic energy, an object’s energy increases if it starts moving. Because of the conservation of energy, the question is, where does the extra energy come from? Is the total energy conserved? That seems not to be right, because relativistic energy alters the total energy, doesn’t it? Thank you.
— David Martin (age 44)

The relativistic case really isn’t much different from the non-relativistic description here. The total energy is conserved, in any particular frame. The kinetic energy may come from reduction of some potential energy, e.g. a weight falling, just as in the classical case. It gets trickier for cosmological general relativistic problems, but special relativistic treatments aren’t tricky.

(published on 08/28/2016)

Follow-Up #10: gravitational potential energy

Thanks Mike. So out in space without gravity, in a given frame the energy that moved an object is the same as the energy it gains from moving.But an object in free fall in a gravity field steadily gains speed, so it gains energy. Where does that extra energy come from? What loses energy, to allow the object to gain energy? Thank you.
— David Martin (age 44)

The gravitational field loses energy. As two masses approach, their fields get closer to adding coherently, making the integral of the square of the field get bigger. There’s a negative energy associated with that field, and thus it gets more negative. It’s very similar to the famouus E 2 +B 2 term in the electromagnetic energy density, except that it has the opposite sign. (This whole answer is in the flat-spacetime approximation, which is all I can handle for this purpose.)

(published on 09/02/2016)

Follow-Up #11: loss of field energy

Thanks. So does the field lose energy because the freefalling object’s position in the field changes, which would be like a relative loss of energy, or does it lose energy from its total, overall energy somehow?
— David Martin (age 44)

The field consists of a part from other objects, plus the part from the one we’re saying «falls». These just add together to make the total field. For simplicity, let’s say the other objects are very massive and at rest with respect to one another, so we can ignore their motions. Falling causes the total field pattern to change, since it involves motion of one object with respect to the others. That’s why the total field energy changes.

(published on 09/04/2016)

The Conservation of Mass

By: Robert W. Sterner ( Department of Ecology, Evolution, and Behavior, University of Minnesota ), Gaston E. Small ( Department of Ecology, Evolution, and Behavior, University of Minnesota ) & James M. Hood ( Department of Ecology, Evolution, and Behavior, University of Minnesota ) © 2011 Nature Education

Citation: Sterner, R. W., Small, G. E. & Hood, J. M. (2011) The Conservation of Mass. Nature Education Knowledge 3( 10 ) :20

Conserving mass

The Law of Conservation of Mass

The Law of Conservation of Mass dates from Antoine Lavoisier’s 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction. If we account for all reactants and products in a chemical reaction, the total mass will be the same at any point in time in any closed system. Lavoisier’s finding laid the foundation for modern chemistry and revolutionized science.

The Law of Conservation of Mass holds true because naturally occurring elements are very stable at the conditions found on the surface of the Earth. Most elements come from fusion reactions found only in stars or supernovae. Therefore, in the everyday world of Earth, from the peak of the highest mountain to the depths of the deepest ocean, atoms are not converted to other elements during chemical reactions. Because of this, individual atoms that make up living and nonliving matter are very old and each atom has a history. An individual atom of a biologically important element, such as carbon, may have spent 65 million years buried as coal before being burned in a power plant, followed by two decades in Earth’s atmosphere before being dissolved in the ocean, and then taken up by an algal cell that was consumed by a copepod before being respired and again entering Earth’s atmosphere (Figure 1). The atom itself is neither created nor destroyed but cycles among chemical compounds. Ecologists can apply the law of conservation of mass to the analysis of elemental cycles by conducting a mass balance. These analyses are as important to the progress of ecology as Lavoisier’s findings were to chemistry.

Hypothetical pathway of a carbon atom through an ecosystem

Figure 1: Hypothetical pathway of a carbon atom through an ecosystem

Because elements are neither created nor destroyed under normal circumstances, individual atoms that compose living organisms have long histories as they cycle through the biosphere. In this depiction, a carbon atom moves from coal buried beneath the Earth’s surface to a power plant and into the atmosphere. It eventually dissolves in water and is taken up by an algal cell, where it is then consumed by a copepod. Labels also indicate the length of time that the atom spends in each compartment.

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Life and the Law of Conservation of Mass

Ecosystems are represented as a network of various biotic and abiotic compartments, connected through the exchange of materials and energy.

Figure 2: Ecosystems are represented as a network of various biotic and abiotic compartments, connected through the exchange of materials and energy.

Every compartment has inputs and outputs.

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Life involves obtaining, utilizing, and disposing of elements. The biomolecules that are the building blocks of life (proteins, lipids, carbohydrates, and nucleic acids) are composed of a relatively small subset of the hundred or so naturally occurring elements. Living organisms are primarily made of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. And each of these important elements cycle through the Earth system.

Ecosystems can be thought of as a battleground for these elements, in which species that are more efficient competitors can often exclude inferior competitors. Though most ecosystems contain so many individual reactions, it would be impossible to identify them all, each of these reactions must obey the Law of Conservation of Mass — the entire ecosystem must also follow this same constraint. Though no real ecosystem is a truly closed system, we use the same conservation law by accounting for all inputs and all outputs. Scientists conceptualize ecosystems as a set of compartments (Figure 2) that are connected by flows of material and energy. Any compartment could represent a biotic or abiotic component: a fish, a school of fish, a forest, or a pool of carbon. Because of mass balance, over time the amount of any element in any one of these compartments could hold steady (if inputs = outputs), increase (if inputs > outputs), or decrease (if inputs Mass Balance of Elements in Organisms

A forest system

Figure 3: A forest system

Because of conservation of mass, if inputs exceed outputs, the biomass of a compartment increases (such as in an early successional forest). Where inputs and outputs are equal, biomass maintains a steady level (as in a mature forest). When outputs exceed inputs, the biomass of a compartment decreases (e.g., a forest being harvested).

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The availability of individual elements can vary a great deal between nonliving and living matter (Figure 5). Life on Earth depends on the recycling of essential chemical elements. While an organism is alive, its chemical makeup is replaced continuously as needed elements are incorporated and waste products are released. When an organism dies, the atoms that were bound in biomolecules return to simpler molecules in the atmosphere, water and soil through the action of decomposers.

Each organism has a unique, relatively fixed, elemental formula, or composition determined by its form and function. For instance, large size or defensive structures create particular elemental demands. Other biological factors such as rapid growth can also influence elemental composition. Ribonucleic acid (RNA) is the biomolecular template used in protein synthesis. RNA has a high phosphorus content (~9% by mass), and in microbes and invertebrates RNA accounts for a large fraction of an organism’s total phosphorus content. As a result, fast-growing organisms such as bacteria (which can double more than 6 times per day) have especially high phosphorus content and therefore demands. By contrast, among vertebrates structural materials such as bones (made of calcium phosphate) account for the majority of an organism’s phosphorus content. Among mammals, black-tailed deer (Odocoileus columbianus; Figure 6) have a relatively high phosphorus demand due to their annual investment in calcium- and phosphorus-rich antlers. Failure to meet elemental demands can lead to poor health, limited reproduction, and even extinction. The extinction of the majestic Irish Elk (Megaloceros giganteus) is thought to have been caused by the shortened growing season that occurred during the last ice age, which reduced the availability of the calcium and phosphorus these animals needed to grow their enormous antlers.

All types of natural and even human-designed systems can be evaluated as ecosystems based on conservation of mass.

Figure 4: All types of natural and even human-designed systems can be evaluated as ecosystems based on conservation of mass.

Individual organisms, watersheds, and cities receive materials (inputs), transform them, and export them (outputs) sometimes in the form of waste.

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Obtaining the resources required for metabolism, growth, and reproduction is one of the central challenges of life. Animals, particularly those that feed on plants (herbivores) or detritus (detritivores), often consume diets that do not include enough of the nutrients they need. The struggle to obtain nutrients from poor quality diets influences feeding behavior and digestive physiology and has led to epic migrations and seemingly bizarre behavior such as geophagy (feeding on materials such as clay and chalk). For example, the seasonal mass migration of Mormon crickets (Anabrus simplex) across western North America in search of two nutrients: protein and salt. Researchers have shown that the crickets stop walking once their demand for protein is met (Figure 7).

Comparison between elemental composition of the Earth

Figure 5: Comparison between elemental composition of the Earth’s crust and the human body

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The flip side of the struggle to obtain scarce resources is the need to get rid of excess substances. Herbivores often consume a diet rich in carbon — think potato chips, few nutrients but lots of energy. Some of this material can be stored internally, but this is a limited option and excess carbon storage can be harmful, just as obesity is harmful to humans. Thus, animals have several mechanisms for getting rid of excess elements. Excess nutrients are released in feces or urine or sometimes it is respired (i.e., released as carbon dioxide). This release of excess nutrients can influence both food webs and nutrient cycles.

Components of an animal

Figure 6: Components of an animal’s mass balance

This black-tailed deer consumes plant material rich in carbon but poor in other necessary nutrients, such as nitrogen (N). The deer requires more N than is found in its food and must cope the surplus a surplus of carbon. As a result, it must act to retain N while releasing excess carbon to maintain mass balance. Carbon and N mass balances suggest that deer waste should be carbon rich and low in N. Boxes show the abundance of N (green boxes) relative to carbon (gray boxes) in the diet, deer, and deer waste products.

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The Physics of Death (and What Happens to Your Energy When You Die)


Even though it’s an inexorable part of life, for many people, death — or at least the thought of ceasing to exist forever — can be a scary thing. The disturbing things that happen to the body during decomposition — the process by which cells and tissues begin to break down post mortem — are bad enough.

But what if instead of looking at death from a biological perspective, we examine it from a physics standpoint? More specifically, let’s look at how our energy is redistributed after we die.

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In life, the human body comprises matter and energy . That energy is both electrical (impulses and signals) and chemical (reactions). The same can be said about plants, which are powered by photosynthesis, a process that allows them to generate energy from sunlight.

The process of energy generation is much more complex in humans, though. Remarkably, at any given moment, roughly 20 watts of energy course through your body — enough to power a light bulb — and this energy is acquired in a plethora of ways. Mostly, we get it through the consumption of food, which gives us chemical energy. That chemical energy is then transformed into kinetic energy that is ultimately used to power our muscles.

A Changed State

As we know through thermodynamics, energy cannot be created nor destroyed. It simply changes states. The total amount of energy in an isolated system does not, cannot, change. And thanks to Einstein, we also know that matter and energy are two rungs on the same ladder.

The universe as a whole is closed. However, human bodies (and other ecosystems) are not closed — they’re open systems. We exchange energy with our surroundings. We can gain energy (again, through chemical processes), and we can lose it (by expelling waste or emitting heat).

In death, the collection of atoms of which you are composed (a universe within the universe) are repurposed. Those atoms and that energy, which originated during the Big Bang, will always be around. Therefore, your «light,» that is, the essence of your energy — not to be confused with your actual consciousness — will continue to echo throughout space until the end of time.

If nothing else can assuage some of the fear of death, the below advice from physicist Aaron Freemen via NPR should do it:

You want a physicist to speak at your funeral. You want the physicist to talk to your grieving family about the conservation of energy, so they will understand that your energy has not died. You want the physicist to remind your sobbing mother about the first law of thermodynamics; that no energy gets created in the universe, and none is destroyed.

You want your mother to know that all your energy, every vibration, every Btu of heat, every wave of every particle that was her beloved child remains with her in this world. You want the physicist to tell your weeping father that amid energies of the cosmos, you gave as good as you got.

And at one point you’d hope that the physicist would step down from the pulpit and walk to your brokenhearted spouse there in the pew and tell him that all the photons that ever bounced off your face, all the particles whose paths were interrupted by your smile, by the touch of your hair, hundreds of trillions of particles, have raced off like children, their ways forever changed by you.

And as your widow rocks in the arms of a loving family, may the physicist let her know that all the photons that bounced from you were gathered in the particle detectors that are her eyes, that those photons created within her constellations of electromagnetically charged neurons whose energy will go on forever.

You can hope your family will examine the evidence and satisfy themselves that the science is sound and that they’ll be comforted to know your energy’s still around. According to the law of the conservation of energy, not a bit of you is gone; you’re just less orderly.

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