# Which came into existance first: Energy or Mass?

## Main Question or Discussion Point

The universe began with the Big-bang and then formed into today's state. But which came first?
Mass or Energy?

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they come together , +gravity is a property of whatever has mass and mass is a property of matter , mass gravitates aka attracts other mass so if you have mass you have gravity , if you have mass you also have energy , have energy you probably have mass , and it goes like this.

in daily life we usually take energy as something abstract and different from the res but in physics that all coems together and is not so different as we may think.

You are saying Energy, Mass and Gravity all came together, at once, right at big-bang?

Drakkith
Staff Emeritus
Energy has mass, so they are not capable of existing separate of each other.
Since gravity is the result of the metric tensor of spacetime, and is bent by the presence of energy in any form, gravity is also present with energy or mass.

Drakkith
Staff Emeritus
You are saying Energy, Mass and Gravity all came together, at once, right at big-bang?
Came together? I don't quite like this terminology, it implies that they may have been separate at some point, which is not true.

If we assume that the big bang was the creation of the universe (which we don't actually know) then mass, energy, and gravity were all created at the exact same time. Of course it is possible that the big bang was not the creation of the universe, and that all three have existed forever.

Came together? I don't quite like this terminology, it implies that they may have been separate at some point, which is not true.
Well, actually by came together I meant 'came into existence together' but thanks for killing any possible confusion.

How come Energy have Mass? Can I say 'mass of this energy is x kg' ?

Drakkith
Staff Emeritus
How come Energy have Mass? Can I say 'mass of this energy is x kg' ?
Absolutely.
You can find the mass of an amount of energy by using the equation: e=mc2
Note that energy NOT in the form of rest mass will only be apparent when you measure the mass of the system as a whole.

By that I mean that the kinetic energy of a baseball will not add to the mass of the baseball itself, but to the mass of the whole system the baseball is in. If we could take the whole baseball field and measure the mass and energy of everything within it, we would find that the kinetic energy of the ball adds to the mass of the whole system.

Absolutely.
You can find the mass of an amount of energy by using the equation: e=mc2
Then if energy has mass then does energies attract one another? Or does matter attracts energy?

Drakkith
Staff Emeritus
Then if energy has mass then does energies attract one another? Or does matter attracts energy?
Energy is not a physical object, it is a quantity. As such, it cannot be attracted by forces, only physical objects like particles can. You cannot have "energies".

Energy is not a physical object, it is a quantity. As such, it cannot be attracted by forces, only physical objects like particles can. You cannot have "energies".
Mass is also not a physical object (am I correct?). Then how can mass be attracted by gravitational force?

By 'energies' I mean - suppose we have a system with energy E1 and another with E2. Will E1 and E2 attract each other?

Dale
Mentor
But which came first?
Mass or Energy?
Mass cannot come before energy, nor vice versa.

Mass cannot come before energy, nor vice versa.
You mean energy came first, then mass? What about gravity?

Dale
Mentor
You mean energy came first, then mass?
No, I don't mean that and I didn't say that. Neither came before the other. Mass and energy always come together. You cannot have one without the other.

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Drakkith
Staff Emeritus
It may help to understand what energy is. Let me try and come up with a decent explanation.

Let's say we have object A that we want to accelerate. So I go ahead and apply a force until this object reaches whatever velocity I want. Applying this force over a distance is what we call work. Using math, I can quantify everything I just did by the formula w=fd. So let's add some numbers.

Let's say I applied 10 newtons of force over 10 meters. 10 x 10 = 100 joules of work done.

So I've done work, accelerated this object, and used math to calculate exactly what occurred. But what if I want to figure out how much work I COULD have done without actually performing it? This is where energy is useful. It lets us know how much work, of any type, we are able to perform given a systems initial conditions.

For example, if I have a pool ball rolling along the table at X velocity, knowing the mass and velocity of the ball I can determine what will happen when that ball hits another ball. In other words, I am predicting how much work that ball can perform on another in the future based on the conditions of the ball (and everything else on the table) in the present. A useful concept, eh?

Now, as we've observed, when objects move around and interact these quantities move around also. That object I performed 100 joules of work on can now be said to have 100 joules of kinetic energy that can be transferred to other objects and even turned into other types of energy, such as radiation or thermal energy.

Let's say we place that moving object in a system where nothing else is moving. Let's also say that our kinetic energy will remain kinetic energy and never be anything else. (Which isn't the case in the real world, but works for our example) If we watch the object collide with other objects we will see that as the energy gets transferred around between everything in the system, we will NEVER have any more or any less than 100 joules of total energy within that system. So while it may get split up between objects, with perhaps one having 50 joules, another having 30, and another having 20, the total will always be 100. So we say that energy is conserved. It never just disappears.

Does all that make sense so far?

Mass cannot come before energy, nor vice versa.
You mean energy came first, then mass? What about gravity?
No, I don't mean that and I didn't say that.
Sorry, I took your 'Nor' as 'Not'.
Anyway, so mass and energy came into existence together. What about gravity?

It may help to understand what energy is. Let me try and come up with a decent explanation.
That was nice. So any system can 'have' energy. But then what is meant by 'Energy has mass' ?

Dale
Mentor
Mass has energy, so it gravitates.

gravity is like the shadow of a man walking on the sunny side of the road , wherever he goes the shadow follows him.
Just as mass/energy came so came gravity it was there since the very first instant if there ever was one.

energy is just one form of mass , when you burn wood you get a flame which produces heat so you can say cook your food or make a hot water to wash yourself.Now when something burns it's a chemical reaction in which part of the mass turns into energy of various kinds , so a little bit of that mass gets lost in the process , it goes away as energy and smoke etc etc.

Not only any system can have energy but all systems have atleast some kind of energy in them.
imagine a tank of gasoline it has mass , you can feel it when you try to pick it up.
Now if you burn it it releases it's energy in a chemical reaction and you end up with no gasoline , so mass has been turned into energy but that mass doesn't disappear the energy it created goes into other systems and interacts with them and adds to their energy , like the heat from the gasoline goes into the surrounding air and the temperature rises , even though it's small and we cannot see it but it is so.

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gravity is like the shadow of a man walking on the sunny side of the road ,
Just as mass/energy came so came gravity it was there since the very first instant if there ever was one.
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energy is just one form of mass,
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Not only any system can have energy but all systems have atleast some kind of energy in them.
Thanks.

So, Energy / Mass and Gravity originated together.

yes indeed , but don't think gravity stands on it's own , where there is no mass and energy there will be no gravity , gravity kinda logically follows wherever there is mass/energy.
Just like the shadow of a man, wherever there is one.

Drakkith
Staff Emeritus
That was nice. So any system can 'have' energy. But then what is meant by 'Energy has mass' ?
Think of mass as the energy content of an object at rest. Whatever its temperature is, whatever is going on inside it, however fast the molecules are bouncing around with their energy, all of that is taken into account with our term "mass". This mass does not change, unlike something like kinetic energy which WILL change depending on how different observers are moving. A proton moving at 0.99c relative to the Earth will see our planet as having an enormous amount of kinetic energy. However, both that proton and another proton moving at 0.5c will agree on how much MASS the Earth has.

Now, that being said, if we shoot a rocket off at 0.01c, that rocket will have a certain amount of kinetic energy. Since that rocket left Earth, the mass of the planet will be reduced by an amount equal to both the mass of the rocket AND an amount of mass equivalent to the rocket's kinetic energy.

So we say this energy has left Earth, our system, and the mass of the system is reduced because it lost energy.

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Thanks everyone.