# Using negative energy

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I've heard about this in the form of the casimir effect and how/somehow it could be used to create a warp drive

http://www.space.com/17628-warp-drive-possible-interstellar-spaceflight.html

But, I'm wondering, how could negative energy be used in this way? What I mean is, what you do is contract the space in front of you, expand it behind you, so the ship isn't moving, the space around it is.

But, what would be the appartus/setup that would make use of the casimir effect to do this? Positive energy is pretty straightforward, you burn coal for example- to heat steam, the turn the turbine to turn the a coil of wire between two poles of a magnet, what would you use to contract the space in front of you and expand it behind you?

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It's nothing technological. Science-fiction if you wish.

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Some experiments have been done to see if warping space/time is possible. So far the results have been inconclusive.

There are more than one way to skin this cat but at the present we do not have the technology implement any of the possibilities...

These sites might give you a handle on what is being done or investigated and there are still more possibilities as well.

EVERY year, the American Institute of Aeronautics and Astronautics (AIAA) awards prizes for the best papers presented at its annual conference. Last year's winner in the nuclear and future flight category went to a paper calling for experimental tests of an astonishing new type of engine.

According to the paper, this hyperdrive motor would propel a craft through another dimension at enormous speeds. It could leave Earth at lunchtime and get to the moon in time for dinner. There's just one catch: the idea relies on an obscure and largely unrecognized kind of physics.

Can they possibly be serious?

The AIAA is certainly not embarrassed. What's more, the US military has begun to cast its eyes over the hyperdrive concept, and a space propulsion researcher at the US Department of Energy's Sandia National Laboratories has said he would be interested in putting the idea to the test.

And despite the bafflement of most physicists at the theory that supposedly underpins it, Pavlos Mikellides, an aerospace engineer at the Arizona State University in Tempe who reviewed the winning paper, stands by the committee's choice.

"Even though such features have been explored before, this particular approach is quite unique," he says.

Unique it certainly is. If the experiment gets the go-ahead and works, it could reveal new interactions between the fundamental forces of nature that would change the future of space travel.

Forget spending six months or more holed up in a rocket on the way to Mars, a round trip on the hyperdrive could take as little as 5 hours. All our worries about astronauts' muscles wasting away or their DNA being irreparably damaged by cosmic radiation would disappear overnight. What's more the device would put travel to the stars within reach for the first time.

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• 1 year later...

I am a theoretical/particle physicist, and this is one of my current projects. Similar to how mass curves spacetime, negative mass would expand space time, and along with negative mass comes negative energy, but the casimir effect is the only example, and negative mass is still eluding many physicists(including myself) who work in this subject.

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You can't have negative mass, any form of energy density is positive.

You can however have negative vacuum with a positive energy density. This is the cosmological constant. The cassimir effect is another example of vaccum, with positive energy density.

Edited by Mordred
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You can't have negative mass, any form of energy density is positive.

You can however have negative vacuum with a positive energy density. This is the cosmological constant. The cassimir effect is another example of vaccum, with positive energy density.

I don't understand how a vacuum can somehow be less than nothing. Please explain.

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A vacuum is a pressure terminology, if the pressure increases you have positive pressure ( contraction). If you have negative pressure, you have expansion. Gravity causes matter to contract= positive pressure. The cosmological constant causes non gravitational bound structures to expand (negative pressure).

However both positive and negative pressure have positive energy density. The vacuum in this application includes a direction a vector. One that is either contraction or expansion. Energy density is a scalar ( magnitude only

).

Cosmology uses the the ideal gas laws, certain forms of particles have different energy density to pressure relations.

See equations of state (cosmology)

https://en.m.wikipedia.org/wiki/Equation_of_state_(cosmology)

http://cosmology101.wikidot.com/universe-geometry

Page 2

http://cosmology101.wikidot.com/geometry-flrw-metric/

Key note the cosmological constant isn't the only cause of expansion, the spatial curvature constant also contributes, so does relativistic radiation,(photons, neutrinos). The cosmological is the most dominant influence in the universe today.

In the past radiation was the most dominant influence, then we had a matter dominant era, finally the Lambda (cosmological constant) dominant era.

Edited by Mordred
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A vacuum is a pressure terminology, if the pressure increases you have positive pressure ( contraction). If you have negative pressure, you have expansion. Gravity causes matter to contract= positive pressure. The cosmological constant causes non gravitational bound structures to expand (negative pressure).

Sounds to me like this is a matter of convention/convenience, much like one can define gravitational potential energy to be negative. It makes certain concepts and calculations easier. Mostly what we're interested in is difference between states, so the choice of zero often doesn't matter. But negative mass doesn't seem to have such flexibility in choosing what we mean by zero.

As far as the Casimir force goes, the vacuum energy in free space diverges; that's not physical, but as above, we're interested in the difference between to configurations. But when you put two conducting bodies near each other you eliminate some of the vacuum states — the difference in energy is calculable.

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... any form of energy density is positive.

Not the case in semiclassical gravity. The expectation value of the energy density can be negative.

I assume that emoallen3433 is working with semiclassical gravity or at least is looking at violations of the various energy conditions.

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You can't have negative mass, any form of energy density is positive.

You can however have negative vacuum with a positive energy density. This is the cosmological constant. The cassimir effect is another example of vaccum, with positive energy density.

I don't understand how a vacuum can somehow be less than nothing. Please explain.

A vacuum is a pressure terminology, if the pressure increases you have positive pressure ( contraction). If you have negative pressure, you have expansion. Gravity causes matter to contract= positive pressure. The cosmological constant causes non gravitational bound structures to expand (negative pressure).

However both positive and negative pressure have positive energy density. The vacuum in this application includes a direction a vector. One that is either contraction or expansion. Energy density is a scalar ( magnitude only).

I was hoping for a clarification, not an explanation of how you are ascribing an unhelpful new definition to an old term.

A few points to consider before reusing your new definitions in public:

Air pressure as generally understood seems to fit quite well your definition of vacuum. Must all future measurements of air pressure (sorry pressure terminology) include its expansion/contraction rate or will you define air pressure as a new sort of pressure terminology?

As vacuum has been preempted, will the volume aspect of space in future be defined as 'space is a volume terminology'?

And so on....

I know you regard science on this site which has not been published in a journal or similar as suitable only for the the trash can but perhaps you have been so busy searching out such posts that you have not had time to apply similar standards to yourself.

I usually stop reading your posts when I come across the equivalent of '1=2 therefor...' but on this occasion perhaps you deserve the sort of help you give many other people.

Edited by Carrock
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I was hoping for a clarification, not an explanation of how you are ascribing an unhelpful new definition to an old term.

A few points to consider before reusing your new definitions in public:

Air pressure as generally understood seems to fit quite well your definition of vacuum. Must all future measurements of air pressure (sorry pressure terminology) include its expansion/contraction rate or will you define air pressure as a new sort of pressure terminology?

As vacuum has been preempted, will the volume aspect of space in future be defined as 'space is a volume terminology'?

And so on....

I know you regard science on this site which has not been published in a journal or similar as suitable only for the the trash can but perhaps you have been so busy searching out such posts that you have not had time to apply similar standards to yourself.

I usually stop reading your posts when I come across the equivalent of '1=2 therefor...' but on this occasion perhaps you deserve the sort of help you give many other people.

This isn't really a new definition at all. People use gauge pressure, which defines atmosphere as the baseline (zero), so a negative pressure is used for a vacuum (of some quality) and a positive number means greater than 1 atmosphere of absolute pressure.

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In this thread 'Mordred said 'You can however have negative vacuum' and corrected it to 'A vacuum is a pressure terminology'

I don't believe you can usefully define vacuum as equal to one of its propertties. In his OP he said in effect that vaccuum is a number. That was his '1=2 thefor...' moment.

If Mordred had read about eg negative gauge pressure and then said 'negative vacuum' and then in a later post confirmed (approx) that vacuum is sYnonymous with pressure I would describe that as a new definition probably created by Mordred's failure to understand the relevant science.

I know (just) enough about vacuum energy to know when I'm reading rubbish; all Mordred's OP does is provide misinformation.

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I said negative mass not vacuum. Rubbish ? Let's see

$w=\frac{\rho}{p}$

Let's use this relationship and describe the early universe prior to inflation then onto inflation.

A radiation dominant universe will expand as the gravitational potential is insufficient to cause a collapse.

The acceleration equation is given as

$\frac{\ddot{a}}{a}=-\frac{4\pi G\rho}{3c^2}(\rho c^2+3p)$

$H^2=\frac{\dot{a}}{a}=\frac{8\pi G\rho}{3c^2}-\frac{kc^2p}{R_c^2a^2}$

where k is the curvature constant. Which during the GUT epock can be largely ignored. Via the equation of state

$p=w\rho c^2$

$\frac{\dot{a}}{a}=-\frac{1}{2}H^2(1+3w)$

From this we can see a radiation dominant universe will expand. In fact it will accelerate when

$w<-1/3(p<-\rho^2/3)$

When the volume sufficiently increases thereby reducing the temperature quarks, gluons and potentially the Higgs boson can drop out of thermal equilibrium. This process may potentially result in inflation as a phase change. The strong force undergoes symmetry breaking.

The simplest version of inflation is via the inflaton which then dominates expansion.

The inflaton is given by $\varphi$, with potential $V\varphi$

The pressure of the field is

$p(\varphi)=\frac{1/2\dot{\varphi}^2}{\hbar c+V\varphi}$

total energy by

$E(\varphi)=\frac{1/2\dot{\varphi}}{\hbar c+V\varphi}$

with equation of state.

$\frac{1/2\dot{\varphi}^2/\hbar c-V\varphi}{1/2\dot{\varphi}/\hbar c+V\varphi}$

How many standard Cosmology equations did I just post that include pressure?

Even inflation itself includes vacuum hence Allen Guths original inflation model is called "False Vacuum". The false vacuum is a higher energy density region that tunnels through a potential barrier to a lower vacuum region "true vacuum"

This equation describes how the universe expands ,it's more commonly called the deceleration equation. As opposed to acceleration equation.

$\frac{\ddot{a}}{a}=-\frac{4\pi G\rho}{3c^2}(\rho c^2+3p)$

note the energy density to pressure terms? That derives from the FLRW metric

Just as an added perspective here is the Einstein field equation stress momentum tensor in the Minkowskii form.

$T^{\mu\nu}=(\rho+p)U^{\mu}U^{\nu}+p\eta^{\mu\nu}$

Even GR uses pressure.

Edited by Mordred
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You can however have negative vacuum

1=2 therefor...

I said negative mass not vacuum.

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I suggest you reread what I wrote.

You can't have negative mass, any form of energy density is positive.

You can however have negative vacuum with a positive energy density. This is the cosmological constant. The cassimir effect is another example of vaccum, with positive energy density.

Just to include the Cassimer effect.

"the Casimir effect produces the equivalent of about 1 atmosphere of pressure (the precise value depending on surface geometry and other factors)."

https://en.m.wikipedia.org/wiki/Casimir_effect

The Casimir effect uses zero point energy which is the lowest possible energy density.

https://en.m.wikipedia.org/wiki/Zero-point_energy

Edited by Mordred
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In this thread 'Mordred said 'You can however have negative vacuum' and corrected it to 'A vacuum is a pressure terminology'

I don't believe you can usefully define vacuum as equal to one of its propertties. In his OP he said in effect that vaccuum is a number. That was his '1=2 thefor...' moment.

If Mordred had read about eg negative gauge pressure and then said 'negative vacuum' and then in a later post confirmed (approx) that vacuum is sYnonymous with pressure I would describe that as a new definition probably created by Mordred's failure to understand the relevant science.

I know (just) enough about vacuum energy to know when I'm reading rubbish; all Mordred's OP does is provide misinformation.

We discuss what our vacuum is all the time in my field. (typical response: 10-9 torr). I don't find the terminology Mordred used to be confusing.

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I think the problem Carrock is having is how we are defining the state of the system.

In cosmology we set the reference point at a state where there is no expansion or contraction.

This is the critical density formula.

$\rho_c=\frac{3H^2}{8\pi G}$

This calculated value is the fulcrum point between expansion and contraction. (Prior to the discovery of the cosmological constant where dark energy may possibly contribute)

A perfectly critically dense universe ( Euclidean-flat) is neither expanding or contracting. However that's also unstable

Edited by Mordred
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Just an FYI on the wiki equation of state they mentioned $\Omega_k$ which is the spatial curvature constant.

However it doesn't cover any great details. it isn't an actual energy density. However it's convenient to consider it as such

$\Omega_k=\frac{\rho_k}{\rho_{crit}}$

where

$\rho_k=\frac{3kc^2}{3\pi G a^2}$

With no subscript, Ω denotes the total mass-energy density in all forms. Via the first equation

$\Omega_k=1-\Omega$

Edited by Mordred
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I think the problem Carrock is having is how we are defining the state of the system.

My 'problem' with you is the usual one - you expect people to have faith in you.

You not only claim not to have used the term 'negative vacuum,' you quote 'negative vacuum' again in your next post.

You could not make it clearer that you expect uncritical faith that you are right.

We discuss what our vacuum is all the time in my field. (typical response: 10-9 torr). I don't find the terminology Mordred used to be confusing.

Clearly moderator swansont has faith in you and I am probably outnumbered, which is a sad way to end a discussion on a forum with 'science' in the title.

As you ignore any criticism you can't refute, this is my last post.

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Sorry to see you go. There is nothing wrong with the term negative vacuum.

Don't take my word for it. I only teach what can be found in standard textbooks. Every one of the above formulas are standard formulas.

You want peer review here ya go.

"If vacuum energy can be negative, why is mass always positive?: Uses of the subdominant trace energy condition"

http://arxiv.org/abs/1310.6203

Now I ask you if a professional peer reviewed article can use the term "negative vacuum". What is wrong with my use of a standard terminology.

My 'problem' with you is the usual one - you expect people to have faith in you.

I don't expect people to have faith in me. The majority of my posts include supporting articles for that reason. You could have easily googled the term " negative vacuum" then add pdf. This would have pulled up dozens of articles that uses the same terminology.

The part you miss is its negative compared to a baseline value

Edited by Mordred
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I have seen 'negative vacuum ENERGY' or 'pressure' many times.

'Negative vacuum', not so much.

Is that what the objection is, or am I missing something ?

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Tbh not sure myself, my only guess is that he doesn't like the principle behind the cosmological constant itself. He once posted a thread on a steady state model he was working on. Which I pointed out that thermodynamics temperature decrease is a strong piece of evidence.

Not positive if his objection is related or not.

(Might explain his objections to my related posts) not including his comments directed at me

Guess he doesn't realize that if I make a mistake, I fully expect and respect corrections

Vacuum already being defined as an energy state, negative vacuum is just a short hand of negative vacuum energy.

Edited by Mordred

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