If All Matter Were Converted to Energy?

Matter is a form of energy already, is it not?

Yes,it is.

^(E=MC²)

My question was basically how much matter is in the universe in baryonic form.

But thanks for the feedback!

NASA says about 4.6%.

I don't know if this answers your question, but it is thought that the total energy of the universe is zero.

The energy of a gravitational field is negative. You have to supply energy to separate all the matter in a gravitating body to infinity. It is believed that the positive energy of matter (E = mc²) is numerically equal but opposite in sign to the negative energy stored in gravitational fields.

"Stephen Hawking explains the concept of negative energy in his book The Theory of Everything (New Millennium 2002): "Two pieces of matter that are close to each other have less [positive] energy than the same two pieces a long way apart, because you have to expend energy to separate them against the gravitational force that is pulling them together," he wrote.

Since it takes positive energy to separate the two pieces of matter, gravity must be using negative energy to pull them together. Thus, "the gravitational field has negative energy. In the case of a universe that is approximately uniform in space, one can show that this negative gravitational energy exactly cancels the positive energy represented by the matter. So the total energy of the universe is zero."

https://www.livescience.com/33129-total-energy-universe-zero.html

I think I understand what I thought you said,but I am not sure I understand what you meant.

Thanks for you contribution.

"... You have to supply energy to separate all the matter in a gravitating body to infinity. It is believed that the positive energy of matter (E = mc²) is numerically equal but opposite in sign to the negative energy stored in gravitational fields.

How certain are you about this? Doesn't seem right.

Gravitational potential energy is well correlated with the inverse of the square of the distance from center of mass, so the most local mass should be the overriding dominant factor. Since escape velocity from any directly observable mass is less than the speed of light, and

E= mc² for converting between mass and energy and

E=1/2mv² for kinetic energy

and since with every but of mass accellerated to escape velocity, the total mass from which the next portion is required to escape is reduced....

It seems that unless there is a lot of mass in back holes in the universe and or that most collections of mass are just above the respective Schwartchild radius, that the the energy from converting all mass would dwarf the negative gravitational potential energy.

How certain are you about this? Doesn't seem right.

I should have said, "according to the zero-energy hypothesis". I don't know how universally accepted it is. One proponent is Steven Hawking, so I suspect it's not totally "off the wall."

From Space.com/live science:

"The zero-energy universe hypothesis proposes that the total amount of energy in the universe is exactly zero: its amount of positive energy in the form of matter is exactly canceled out by its negative energy in the form of gravity.^[1][2]"

https://en.wikipedia.org/wiki/Zero-energy_universe

"What's the Total Energy In the Universe?

Considering the amount of energy packed in the nucleus of a single uranium atom, or the energy that has been continuously radiating from the sun for billions of years, or the fact that there are 10^80 particles in the observable universe, it seems that the total energy in the universe must be an inconceivably vast quantity. But it's not; it's probably zero.

Light, matter and antimatter are what physicists call "positive energy." And yes, there's a lot of it (though no one is sure quite how much). Most physicists think, however, that there is an equal amount of "negative energy" stored in the gravitational attraction that exists between all the positive-energy particles. The positive exactly balances the negative, so, ultimately, there is no energy in the universe at all.

Negative energy?

Stephen Hawking explains the concept of negative energy in his book The Theory of Everything (New Millennium 2002): "Two pieces of matter that are close to each other have less [positive] energy than the same two pieces a long way apart, because you have to expend energy to separate them against the gravitational force that is pulling them together," he wrote.

Since it takes positive energy to separate the two pieces of matter, gravity must be using negative energy to pull them together. Thus, "the gravitational field has negative energy. In the case of a universe that is approximately uniform in space, one can show that this negative gravitational energy exactly cancels the positive energy represented by the matter. So the total energy of the universe is zero."

https://www.livescience.com/33129-total-energy-universe-zero.htm

Here is a calculation that comes up with some values for the observable universe that you might find interesting:

http://www.curtismenning.com/ZeroEnergyCalc.htm

Thanks for the links!

A lot of stuff falls between the cracks in the planks of memory over time.

A great review!

If the universe is expanding,due to positive energy,then the amount of negative energy must also be increasing to achieve balance,so more matter must be constantly created to balance the equation,or there is a lot more matter in the universe than we expect.
Therefor the "big bang" expansion must be still occurring,spewing energy and matter into the "sphere" of our universe,including dark matter and dark energy.
Nothing plus nothing equals nothing,so reality must really "be an illusion, but a very convincing one",as Einstein said.
Perhaps dark matter is merely the "Ghost" of matter that went into a black hole,everything stripped bare of the matter except it's gravity(negative energy).

I appreciate the links and the time you put into your answer.

This idea of matter and other interconvertable forms of 'positive' energy being offset exactly by the 'negative' energy of gravity interacting with mass still seems have some serious problems.

Woe be unto me to question Hawkings, but the idea seems like it requires a definition of total energy so convoluted as to render it useless.

One problem is with the idea that gravitational potential energy can be shown to be negative because energy must be expended to separate two objects with gravitational attraction. A similar argument could be made about a number of things other than gravity.

Any two masses together stationary to the same resting frame require energy to separate. Are we then to consider inertia as having an equivalent negative energy associated?

What about material strength, would that also have a negative energy associates? It takes energy to overcome.

We also have evidence that in some binary systems, a dense neutron star's gravity will feed off a large young star by ripping away some of the outer layers pf gas. This is gravity being overcoming gravity...which one gets to be the negative one now?

Also, what happens to conservation of energy in matter/energy conversions related to proximity to large masses? If gravity is truly has a negative associated energy shouldn't we see variation in minimum energy photons able to yield pair production based variations in gravitational field?

.

Not sure how that became anonymous. It certainly wasn't intended.

When trying to understand the universe by using a model, one should heed the aphorism attributed to George Box:

All models are wrong. Some models are useful.

i'm a fan of George E.P Box and I find his most famous quote a particularly useful model itself.

I wonder if he would have guessed how wrong some models of today could be....

I was going to say that AP#1 is coming up in the world. Good post.

Here are some of my thoughts:

Most of the confusion, I think, is defining what zero potential energy is. We mainly deal with potential energy differences, so it makes no difference where the zero point is. A difference in potential energy is converted to or from a form of positive energy.

I think the zero-energy hypothesis is that "the universe started with zero total energy and the sum is still zero". (Whether this is true, I think, nobody knows for sure, but zero is an easier number to explain than some other amount.)

Gravity potential energy is negative because it takes positive energy to separate gravitating bodies. As we add energy, the gravitational field becomes weaker. If all the particles of the earth were dispersed to infinity, its gravitational energy would increase to zero.

https://en.wikipedia.org/wiki/Negative_energy

Static electric and magnetic fields do not operate this way. The energy is proportional to the square of the field strength and is always positive. Kinetic energy is proportional to velocity squared and is always positive.

Materials are bound together by electric forces which have positive energy stored in them. Breaking apart a material results in a greater total energy stored in these fields, at least temporarily. (Think about separating two oppositely charged capacitor plates.)

A neutron star capturing material from its binary partner would be transferring some gravitational energy to the material which is moving to a lower potential and acquiring kinetic energy. The potential energy of the gravity field becomes more negative and the gravity well gets slightly deeper and stronger. More of the gravity field would be due to the neutron star and slightly less to the partner star.

I read PhD Hawking's book for laymen (like me) and disliked the concept of negative energy because of how easy it can be to misunderstand. The sign of energy is purely subjective. Let me put this in an economic perspective to make my point. The payroll for a business is a negative cash flow. A paycheck is a positive cash flow for the employees. If my memory is correct PhD Hawking does make this distinction that unlike the electric charge of a particle the positive or negative sign for an energy transfer was purely subjective.

I also dislike the idea that the absolute sum of all energy is zero. The sum of all matter in the universe is clearly not zero. Why would energy be different. Our observations do not show there are anti-matter galaxies to make up the difference to make matter a zero sum. People have looked very hard in multiple ways and not seen signs of vast amounts of anti-matter.

Actually, matter is counted as positive energy, m=E/c².

It does seem counterintuitive that gravity has negative energy. It's like a hole and the more you drop into it, the deeper it gets!

We're all taught that potential energy and kinetic energy get interchanged when, for example, a ball is thrown in the air. All well and good. But potential energy (PE=mgh) increases with height, with the distance away from the gravitating body (the earth). The lower you go into the gravity well, the lower the potential energy.

As gravity gets more intense, the potential energy gets lower. To equate the potential energy with the strength of a gravity field, the energy stored in a gravitational field has to be negative. The stronger the field, the more negative. The energy density of the gravitational field should be zero at an infinite distance.

From hyperphysics:

"Gravitational Potential Energy

The general expression for gravitational potential energy arises from the law of gravity and is equal to the work done against gravity to bring a mass to a given point in space. Because of the inverse square nature of the gravity force, the force approaches zero for large distances, and it makes sense to choose the zero of gravitational potential energy at an infinite distance away. The gravitational potential energy near a planet is then negative, since gravity does positive work as the mass approaches. This negative potential is indicative of a "bound state"; once a mass is near a large body, it is trapped until something can provide enough energy to allow it to escape. The general form of the gravitational potential energy of mass m is:

where G is the gravitation constant, M is the mass of the attracting body, and r is the distance between their centers.
This is the form for the gravitational potential energy which is most useful for calculating the escape velocity from the earth's gravity."

http://hyperphysics.phy-astr.gsu.edu/hbase/gpot.html

The zero-energy universe hypothesis is that the negative energy of gravity and the positive energy of mass and other positive energy (radiation, motion, etc) adds up to zero. It's a hypothesis, a scientific guess on what 'feels right'.

I didn't say gravity has negative energy was wrong, I said I disliked it because of how easy it is to misinterpret. Just like a foolish businessman claiming the cause of a failing business is the payroll. Payroll is part of a businesses balancing act but it is not the whole picture.

Just look at how much rehashing of fundamental Newtonian gravity we are covering here.

Thanks for the discussion.

"... Static electric and magnetic fields do not operate this way. The energy is proportional to the square of the field strength and is always positive. .."

I'm with you on the electic field part. Magnetic fields seem similar to gravitational fields though. The change in magnitude with distance is not the same, but the influence does decrease toward zero with increasing distance. Also both require energy to overcome attraction...

What am I missing here? What are you looking at that makes magnetic fields seem obviously positive.

The energy density of an electric field is 1/2 ε E², where ε is the permittivity and E is the electric field strength.

The energy density of a magnetic field is 1/2 B²/μ, where μ is the permeability and B is the magnetic flux density.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/engfie.html

In both of these cases, energy has to be positive due to the square term. The greater the strength of the field, the greater the energy.

If a magnet attracts an iron ball, as the ball is drawn in part of the energy in the magnetic field is converted to kinetic energy and the magnetic field becomes weaker.

The energy in a gravitational field is negative:

https://en.wikipedia.org/wiki/Negative_energy

If a planet attracts an asteroid, the negative energy of the gravity field becomes more negative transferring energy to the asteroid and making the gravity field even stronger, and so this is how it is different from an electric or magnetic field.

"... If a magnet attracts an iron ball, as the ball is drawn in part of the energy in the magnetic field is converted to kinetic energy and the magnetic field becomes weaker...."

Magnetic field strength does not generally decrease as a piece of oron is drawm closer. Magnetic field strength varies inversely with somewhere between the square and cube of the distance.

I see what you are saying with about the squared term, but simply playing around with magnets for a short period would make it abundantly obvious that the field does not become weaker as a lump of iron is drawn closer. So if magnetism and gravity are sufficiently similar and the energy in a magnetic field cannot be negative, perhaps the energy in a gravitational field also cannot be negative...

For electric fields of point charges of opposite charge, the field is actually very much like gravity, varying inversely with distance, requiring energy to separate, etc.

The strength of the electric field between two oppositely charged infinite area parallell charged plates might be invariant with separtion distance, but I'm not sure gravity wouldn't behave very similarly and be roughly separation distance invariant for two infinite area parallel masses.

My explanation could stand some improvement. Let me try again...

What I was trying to say was that electric fields and magnetic fields have positive energy whereas gravity fields have negative energy. This can be seen by the energy needed to create these fields.

To create an electric field between the plates of a capacitor requires electrical energy, current flowing against the voltage on the capacitor, which is stored as energy in the electric field.

To create a magnetic field in an inductor also requires electrical energy. As the current increases, there is an opposing voltage and the current flowing against this voltage provides the energy that is stored in the magnetic field.

To create a gravity field requires bringing matter together in one place. This does not require energy, but in fact, releases energy. So the energy stored in the gravity field is negative.

That last part is a good argument.

Thank you.

Observe a bubble as it rises through a liquid.

A viscous liquid is easier to observe,like glycerin, for instance.

It starts at the bottom,very small,and slow moving,then as it rises,it becomes larger and the rate of growth increases as it rises.

The density of the contents of the bubble changes as it expands.

Imagine that we live on the surface of a bubble,and that all of our information is derived from the surface only.

The surface layer is our "dimension".

Imagine that the singularity was a small bubble of space time,and as it expanded,the surface area becomes larger in the most efficient shape:a sphere.

All objects at the boundary of the sphere get futher apart as it rises.

No entity on the surface can determine the center,because it can only see within the narrow confines of the surface,and every object seems to be at the center of everything in the bubble universe.

That seems to fit the analogy of our expanding universe,except for one thing;The matter and energy density remain constant according to our measurements.
Of course they would seem constant,we do not have an "outside the bubble layer" reference point.

All of our measurements would be affected in the same manner as the rest of the universe.

A billion years ago,a meter would,from an "outside point on view," be shorter than it is today.

We could not tell it though,because we are trapped on the surface of the bubble,and to our way of thinking,a meter is a meter is a meter,and always has been.
A scale drawn on the outside of a bubble would maintain the same relative relationship between divisions,but when viewed from the outside,it is actually getting larger.

The density,or space between and two objects would appear to be constant.
The surface boundary of the bubble is defined by the speed of light.In order to break out ,we would need to exceed the speed of light,which is currently not possible.

A Cephid star is used as a means to measure distance,but when we look at an object billions of parsecs away, we are looking at where it used to be,not where it is "now"(There is no "Now"), as Einstein said.

I am sure that these ideas have been better stated by others,and this is just a Rednek way of expressing my views of the universe, as I see it.(Relatively speaking)

I am open to suggestions and corrections on my misconceptions and ideas,but it will be a while before I get back here,trapping season is almost over,and I have a lot of trap lines to maintain.

Interesting.

So, if a unit of length like a meter is longer today than it was billions of years in the past, would that mean the speed of light as measured in meters per second is

1. slowing down ....because it has a set real speed and as meters elongate fewer meters are traveled per second.

2. Remaining the same...because the same stretching of the meter is stretching the distance light travels per unit time.

3. Speeding up .... because the universe is shy in its most private parts and fancying itself to be chaste and unknowable.

4. Some combination of speeding up at times and slowing at others.

5. Unknowable because our most fundamental units of time and distance are based on things affected by the speed of light. At most we might think we notice it taking slightly longer for the sun rise in the morning, or for the bulb to illuminate after we flip the switch.

I think number 2, it remains the same. The speed of light is its speed through space, and the consensus is that that doesn't change in time.

The cosmological red-shift results because space has expanded between us and distant galaxies, causing the spectral lines to be shifted in frequency by an amount proportional to distance.

https://en.wikipedia.org/wiki/Metric_expansion_of_space

Interesting.

Consider that photon that was emitted several million years ago - (I don't like billions as the we immediately run into definitions) - it has electric and magnetic fields associated with it. Presumably, the energy of the photon remains the same along its trajectory ( or its observed frequency would change) and in consequence the energy stored is reflected in the strength of those fields as they vary amongst themselves along that trajectory.

In fact, the frequency of the photon does change. Spectral lines from far away galaxies are red-shifted proportional to the distance by a factor of Hubble's constant. The accepted theory is that this is due to the expansion of the space between us and the source.

http://astronomy.swin.edu.au/cosmos/c/cosmological+redshift

You bring to me an interesting nuance I have apparently frequently misunderstood which led me to a few false paradoxes. The observed spectral red shift of distant objects is not attributed solely to Doppler shifting but to also Einstein's supposed folly of spatial expansion (more space being created). I wonder if the comparison of the two paths of light from a distant galaxy or quasar being bent by a gravitational lens is how this was confirmed?

There are three different forms of red-shift. Doppler red-shift occurs when the source is moving away. Gravity red-shift occurs when the source is deep within a gravitational field and the photons lose energy. Cosmological red-shift is caused by the expansion of space during the time that the light was moving from the source, which expands the wavelength of the light.

https://en.wikipedia.org/wiki/Redshift#Measurement,_characterization,_and_interpretation

I don't know of a connection between cosmological red-shift and gravitational lensing. Gravity would focus light whether the universe were expanding or not.

I did know of gravitational red-shifts. This shouldn't apply in my proposed gravitational lens scenario for the source is not in the gravity well doing the lens effect.

If you think about how light is diffracted at the edge of slits - see Youngs Slits and single slits. The wave theory geometers will point out that each point on a wavefront is the source of other wave(let)s. and hence the light can bend around the corner or edge.

If you now think of single photons, some will go straight through the slit but a small number will interact with the atoms/molecules that make up the material of the slit and will be diverted, where they're not attenuated, and in bulk they will produce a seies of fringes of light and dark with a bright centre point.

So what about 'gravitational' lensing ? OK you've got some light that was coming straight at you and some that was going to miss. If an object, star, planet, whatever gets between you and the light, then the straight on stuff will be attenuated to nothing and that approaching the edge will interact with the atoms in the atmosphere, if it has one, and there will be a corresponding refraction, probably more from the denser regions and tailing off in the higher less dense regions.

But what happens if there is no atmosphere ? That's when you have to start tweaking your model maybe with what Erik Verlinde calls Dark Energy, and what Martin Rees just alludes to in his 'Just Six Numbers' by not giving it a name in case someone thinks it's (A)ether.

Well a lot of photons were converted to antimatter....and then you have dark matter and dark energy....so no....

How much matter would it take....? A lot more...

http://www.astronomynotes.com/cosmolgy/s6.htm

You are a tough act to follow,SE.

I have not digested everything you linked to,but I am nibbling away at it,bit by bit.

Thanks for your always valuable input.

That would make it the "Big Suck," i.e.: the inverse of Big Bang.

If all matter was converted to energy - where would anyone stand?

On their merits?

Stand and deliver.....

Merits are probably exclusively nontransferable and certainly nonfungible. I might be motivated to stand, but merits cannot be willfully given nor forcefully taken.

Dick Turpin. the famous highwayman used that line

As I understand 'stand and deliver' it was a signature of highwaymen meaning essentially 'give up your valuables' to those they were robbing.

Yes, When I was a kid in London in 1946 we did not play cops and robbers - we played highwayman, and Dick Turpin was the hero....

Highwayman vs ? Gumshoe?

We played 'cowboys vs indians' either that or 'army'.

I grew up very poor.

No toys at all.

If I hadn't been a boy,I wouldn't have had anything to play with.

You seem to be asking if all the baryonic matter was put in one place and exploded, would it be enough to propel the existing galaxies at their present rate of recession. But that's not the kind of expansion we have. It's the space that's expanding, not matter traveling through space. I'm not sure there's any energy involved. Another thing to consider is that the total universe is thought to be a million times bigger than the observable universe. There is no way to calculate the total matter beyond our observations.

We have to be careful bandying about terms like space.

Space is the volume, probably possibly infinite, in which our universe (and if there are others, then those also) reside.

So I guess you mean our Universe is expanding, and if, as has been suggested elsewhere, that our Universe is a sea of interconnected blobs of Energy, from which matter has condensed then we must ask ourselves whether matter is a lumpy thing that hurtles through this sea, clearing a path to traverse through, or does it keep absorbing the energy blobs and rejecting others along its trail.

In this scenario the expansion would cause the energy blobs to be stretched which would appear to reduce the total energy of the Universe, whilst condensation into matter would have the opposite effect.

I haven't seen Jorrie's input for some time. Is he on another forum ?

"...Space is the volume, probably possibly infinite, in which our universe (and if there are others, then those also) reside. ..."

Not so sure that our universe resides 'in' space to the extent there might be space outside our universe. 'Universe', IMHO, pretty much encompasses everything that can effect, interact with or influence other stuff in a particular tangible reality....including volume.

If there are other universes, sharing space is kind of anti-themetic to the idea of a universe.

Truth is subjective,and relative,according to Einstein,and who am I to argue with him?

"Reality is an illusion,but a very convincing one." he said;Therefor everything is subjective.

A good baseball base ref looks at the base when a runner is coming and listens to the sound of the ball hitting the glove.He calls the player "OUT".

A spectator sees the action from across the field,and it appears to him that the ball got there after the runner,and declares he was "SAFE".

There is an argument,and both men know absolutely that what they saw is the "Truth"

Both parties are right,from their perspective,but the base coach was closer to the "truth".

A video+audio taken from both positions would show different results if the player's foot was not visible.

"If we all worked on the assumption that what is accepted as true is really true, there would be little hope of advance." -- Orville Wright

"...."Reality is an illusion,but a very convincing one." he said;Therefor everything is subjective...."

Your Q.E.D. could use some more Demonstradum.

I refer you to Einstein's theory of Relativity for a starting point for your illumination and edification in re: Einstein's quote.

To veer slightly into a philosophical analogy,there is a Chinese story of a man that fell asleep under a tree and dreamed he was a butterfly.

When he awoke he wasn't sure if he was man who had dreamed of being a butterfly,or a butterfly still dreaming that he was a man.

I also remember a sci-fi story from many years ago about an android that thought he was human.

When his creator tried to convince him otherwise,he presented the same arguments that anyone would:He had all of these memories from childhood,all the people he had met,the schools he had attended,all of his classmates,the jobs he had.

He could not believe that all of his memories had been installed only moments before.

subjective: influenced by or based on personal beliefs or feelings, rather than based on facts

Merely because Einstein used the word 'relativity' in naming his well vetted models of reality, and some definitions of 'relative' might be relatively close to 'subjective' is not enough to establish that the Universe or even just special or general relativity are reasonably labled as 'subjective".

I find no contradiction in that a decent functioning model of human behavior might behave in a way mimicking stubborn refusal to accept it is anything other than human.

About butterfly sense of self and other butteryfly pschology, I know only that I do not know.

I simply agree to disagree with you.

Subjectively,of course.

Objectively, your replies are merely terribly inconvenienced electrons,eliciting a photon emission from a phosphor trapped on a surface, or a PN junction(LED) that has been likewise excited to emit a photon by applying voltage (pressure) to a doped layer of silicon.

So objectively,you cannot prove that you exist;you could merely be a very convincing AI entity.

Likewise,you cannot prove the same about me--nor can I .

Of course,you would deny it vehemently,(as would I),and even refuse to believe it .

Of this last part, my disagreement is not an insistence of the verifiablity that you or I exist as whatever the preferred embodiment might be.

My disagreement here would be with the false dichotomy you assert in

"....,you cannot prove that you exist;you could merely be a very convincing AI entity ...."

My existence is not at the mercy of any uncertainty about the proper label for what is believed to be my true nature. I wouldn't exist any less if my motivations and ponderings originate in a computational machine than is flesh and blood.

"Thou dost protest too much,Methinks "

How do you know that I am not an AI,learning from my interactions?

(Notice I even added the smile icon,like humans do?)

Pretty good for a machine,huh?

In order to assuage your distress of the misuse of the word "universe" I will refer to the current observable limits to our existence as a "Bubbleverse",meaning confined to within a bubble, only one of what may be an infinite number of "Bubbleverses".

So please substitute"Bubbleverse" instead of "Universe" in all of my previous posts that create ambiguity in my meaning.

We cannot observe anything outside of our bubble,but that does not mean that others do not exist,and they may interact with each other,causing unexplained effects within the "surface" or interiors of other "bubbles".

IMHO:

These "Bubbleverses" may be within an even larger bubble,which is rising in some unknown media,where the external pressure is decreasing over time,(like a bubble rising through water) giving rise to our expanding spacetime bubble.

No internal energy required for expansion,simply a decrease in "outside" pressure.

Duly noted. Substitution made.

If all the baryonic matter in the universe were converted to energy could cosmic expansion be detected?

Your question reminds me of the question about angels dancing on the head of a pin.

No, because you need to account for the large (and subjective) Non-baryonic matter component.

This really is a case of x+y+a(w)=z

where x is baryonic matter (whose value is a guess), y is Non-baryonic matter (whose value is also a guess) and there may be another as yet unknown w that contributed.

If not, how much matter would take?

More than a little and less than too much.

The Simpsons explained it best in the Gabbo (ventriloquist dummy children's entertainer) Episode when Homer was trying to work out what GABBO was when given only the word Gabbo repeated on TV with no context.

Just be wary of building a hypothesis on incomplete data and the unproven guesswork of others, it is fraught with peril.

Some more food for thought: http://www.foxnews.com/science/2018/03/05/stephen-hawking-says-knows-what-happened-before-dawn-time.html

https://en.wikipedia.org/wiki/Heat_death_of_the_universe

Day's later and a lot of discussion..

Not one reply has been converted to a good answer.

<...Energy...> isn't a substance; it is a capacity to do work. So, in a universe where none of the matter were to remain, then there would be no scope in that universe for work to be done. So the expansion will have completed, and a velocity at that moment would be incalculable, as there would be nothing to measure against and no-one around to carry out a measurement.