# The massless universe

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So I've been running a lot recently.  And running causes the mind to wander, and wonder.  Here are some wanderings:

Are all quantum observers required to be massive?

Can something without mass, cause or contribute to waveform collapse of an another observable?

Must all massless things in the universe move at the speed of light, relative to the massive things?

Must all things that move in the universe at the speed of light be massless?

Do all massive things move at the same speed relative to a massless thing?

Do all massive things need space?

Do any massless things need space?

Do all massive things experience entropy?

Do massless things experience entropy?

Does time matter to massless things?

Do massless things experience spacetime ?

Does a massless universe  require spacetime?

How many dimensions does a massless thing need?  EG, a photon has property of wavelength and a frequency, so at least 2 dimensions.  Could its "movement" through spacetime be a property of spacetime rather than of itself?  That is, if it didn't have the property of c relative to massive things, because massive things didn't exist, would it still have the property of c?

That's many questions to roughly the same thoughts that were bugging me as I was running.  Ill be running again tomorrow!

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Those are big questions. Understanding requires simplification not complexification.

Hidden variables, what are they? They are hidden!

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Having no mass is shortcut of having no rest-mass. It means that object have rest-frame of reference. https://en.wikipedia.org/wiki/Rest_frame

Objects with rest-frame can change their frame of reference by acceleration in specified direction.

Two or more objects in the same frame of reference appear motionless to each other.

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16 minutes ago, AbstractDreamer said:

Are all quantum observers required to be massive?

An observation, in quantum theory, is just an interaction. Photons interact ("observe") and are massless.

17 minutes ago, AbstractDreamer said:

Can something without mass, cause or contribute to waveform collapse of an another observable?

Yes. A photon could interact with something.

17 minutes ago, AbstractDreamer said:

Must all massless things in the universe move at the speed of light, relative to the massive things?

Must all things that move in the universe at the speed of light be massless?

Yes and yes.

18 minutes ago, AbstractDreamer said:

Do all massive things move at the same speed relative to a massless thing?

That doesn't really make sense that way round.

All massless things travel at the same speed for all (massive) observers, whatever the speed of the observer. Therefore there is no speed that is "relative to the speed of light".

20 minutes ago, AbstractDreamer said:

Do all massive things need space?

Do any massless things need space?

No. Needing space is a characteristic of fermions (which all have mass). Bosons can all occupy the same space (they can overlap or pass through one another). And there are bosons with mass.

But all massless things are (I think) bosons, and so no't need space.

(Assuming that is what you mean by "need space"; or maybe they just need to get away from it all for a while!)

22 minutes ago, AbstractDreamer said:

Do all massive things experience entropy?

Do massless things experience entropy?

I think entropy only applies to systems, which probably always have mass. But I'm not going to attempt to answer this!

24 minutes ago, AbstractDreamer said:

Does time matter to massless things?

Do massless things experience spacetime ?

It is often said that photons, for example, don't experience time because as you get closer and closer to the speed of light, time dilation increases and it would seem logical to say that it becomes infinite for photons (ie. that no time passes for them).

But, mathematically, that is wrong because there is no valid frame of reference for something travelling at the speed of light. If you try and do the related math you end up dividing by zero.

And what does it mean for a photon to "experience time" anyway? They are unchanging so it makes no difference.

29 minutes ago, AbstractDreamer said:

Does a massless universe  require spacetime?

I would say that a universe requires spacetime because without that it would be zero-size and exist for zero time; in other words it wouldn't exist.

But, using the math of GR, you can define a universe with no mass or energy in it; just spacetime. These "vacuum solutions" to the Einstein Field Equations are useful for exploring aspects of the theory.

32 minutes ago, AbstractDreamer said:

How many dimensions does a massless thing need?  EG, a photon has property of wavelength and a frequency, so at least 2 dimensions.

Wavelength and frequency are not independent, so they would only be one dimension (if you can count them as that, which you may be able to).

33 minutes ago, AbstractDreamer said:

Could its "movement" through spacetime be a property of spacetime rather than of itself?  That is, if it didn't have the property of c relative to massive things, because massive things didn't exist, would it still have the property of c?

Interesting question...

3 minutes ago, Sensei said:

Two or more objects in the same frame of reference appear motionless to each other.

And that's another good reason why a photon does not have a valid frame of reference: two photons moving in the same direction should be in the same frame of reference, because they are both moving at c. But every observer must see a photon moving at c so both photons would see the other one moving at c and so they cannot be in the same frame of reference. The contradiction arises from trying to consider the speed of light as a valid frame of reference.

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Much appreciated for such direct answers!  I will ponder your information and see what further inconsistencies and contradictions arise in my layman imagination.

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Posted (edited)
2 hours ago, AbstractDreamer said:

Do all massive things experience entropy?

Do massless things experience entropy?

I don't know exactly what you mean with 'experience.' Systems of both massive or massless particles contain entropy, a black hole contains entropy of a very different kind, and even for one quantum particle entropy can be defined in terms of its wave function. Entropy, at the most fundamental level, is defined when the distinctions among different dynamical states are lost. Entropy is the opposite of information.

The total entropy of the visible universe in cosmology approximately equals the number of photons, about 10^90. A gas of photons contains entropy. So I suppose the answer to both questions is yes.

I've just answered the one that Strange passed on, but he was spot on when he said it's about 'systems.'

Edited by joigus

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13 hours ago, joigus said:

I don't know exactly what you mean with 'experience.'

Well let's see.  From what I understand,  EM radiation is affected by curvature. So in this sense, massless EM radiation experiences spacetime.  But is it possible it is only affected by how it is observed by massive things?  That is, although it is massless, it has properties that "only belong" in the massive universe.  For example, its velocity is a constant determined by local curvature in the massive universe, but if it is not a valid frame of reference in itself then velocity is an invalid property of anything existing in the massless universe.  So velocity is a property that only "makes sense" or "takes on a value" in the massive universe. So while EM radiation seems to effect a change in velocity due to curvature, it's not actually a property belonging to the radiation, and therefore no "experience".

Now consider its wavelength.    If space, volume, distance, length and time are all part of the same continuum, then is waveLENGTH a massive property too?   What properties of a photon actually define what it is in its own universe?   Lets say there is a "red" wavelength photon and a "blue" wavelength photon, both with the massive property of c.  If we removed spacetime physics, then c would not make sense, and so would "red" and "blue".  So what is there left to differentiate the two photons?  What is left of the universe without space time?  There must be SOMETHING left!

16 hours ago, Strange said:

And what does it mean for a photon to "experience time" anyway? They are unchanging so it makes no difference.

This "experience" of time I'm referring to is really about leading to whether the existence of time (and spacetime) is a prerequisite for masslessness.

15 hours ago, Strange said:

No. Needing space is a characteristic of fermions (which all have mass). Bosons can all occupy the same space (they can overlap or pass through one another). And there are bosons with mass.

If two bosons have values in the higgs field and then occupy the same quantum state of position, how do they retain their original higgs values when they separate?

What relevance or significance does space, position and location have for bosons?

15 hours ago, Strange said:

But all massless things are (I think) bosons, and so no't need space.

So if we removed all massive things from universe, do the physics of spacetime have any relevance?

If we removed or changed the physics of spacetime, would that affect the nature of any massless things?

16 hours ago, Strange said:

I would say that a universe requires spacetime because without that it would be zero-size and exist for zero time; in other words it wouldn't exist.

I would argue, a universe absent of spacetime requires that anything that might exist within it may have a value for size or for time but that such values are redundant and just meaningless information.  If the presence of spacetime gives meaning to space and time values, then the absence of spacetime removes that meaning.  Zero size and zero time has meaning and meaning requires presence.

16 hours ago, Strange said:

But, using the math of GR, you can define a universe with no mass or energy in it; just spacetime. These "vacuum solutions" to the Einstein Field Equations are useful for exploring aspects of the theory.

I think perhaps I should have started this thread in the quantum fields topic.    GR describes spacetime and gravity through relationships between how things interact on a macro scale.   I wanted to explore how the universe presents to massless things.

Is spacetime a prerequisite for massive or massless things to exist?

Do massless things have any non-spacetime properties?

Do massive bosons have a gravitation effect?

If spacetime is a continuum and gravity curves spacetime, why is spacetimegravity not a continuum?

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Posted (edited)
31 minutes ago, AbstractDreamer said:

Well let's see.  From what I understand,  EM radiation is affected by curvature. So in this sense, massless EM radiation experiences spacetime.  [...]

Now consider its wavelength.    If space, volume, distance, length and time are all part of the same continuum, then is waveLENGTH a massive property too?   What properties of a photon actually define what it is in its own universe?   Lets say there is a "red" wavelength photon and a "blue" wavelength photon, both with the massive property of c.  If we removed spacetime physics, then c would not make sense, and so would "red" and "blue".  So what is there left to differentiate the two photons?  What is left of the universe without space time?  There must be SOMETHING left!

OK, but you're drifting away from entropy.

I mean, electrons, photons or pi mesons can 'experience' curvature (and there I do accept your term,) but not entropy, as entropy is a property of your level of description. It's to do with lost information, and particles don't lose any information AFAIK. Or the concept of them 'experiencing loss of information' doesn't seem a reasonable physical concept.

What entropy growth (or information loss) has to do with is a quite abstract but useful concept that is called 'volume of phase space.' It is a measure of the amount of information that a physical system contains just because of the fact of being in a certain dynamical state. This 'volume of phase space' is neither lost nor gained; it's constant. Just constant. Entropy is the part that is hidden to my description.

We could say,

$S=\textrm{constant}$

This is sometimes called 'microscopic entropy' and its conservation is the most fundamental physical principle there is. Now, it just so happens that many things go on without us knowing about it. Only because there is a fiduciary value of a quantity that stays constant and I can associate with the information content of a system, can I speak about loss of information. Otherwise it wouldn't make any sense.

I hope that helps to clarify the situation as to the entropy. It's a really confusing concept, and the great mathematician John V Neumann once said that physicists don't know what entropy really is. No longer the situation, I think.

Edited by joigus

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2 minutes ago, AbstractDreamer said:

This "experience" of time I'm referring to is really about leading to whether the existence of time (and spacetime) is a prerequisite for masslessness.

I think when you get to the point of imagining a model without time, or worse without space, then it becomes hard to give realistic answers. However, mass is not defined in terms of time or length. It is an independent quantity unlike, for example, force which is defined in terms of mass, length and time. https://en.wikipedia.org/wiki/Dimensional_analysis

6 minutes ago, AbstractDreamer said:

If two bosons have values in the higgs field and then occupy the same quantum state of position, how do they retain their original higgs values when they separate?

What does "values in the higgs field" mean? The Higgs mechanism is responsible for the mass of particles, including those bosons that have mass.

7 minutes ago, AbstractDreamer said:

What relevance or significance does space, position and location have for bosons?

Well, their position can be defined. In as much as the position of any quantum particle can be defined; i.e. when it s measured.

8 minutes ago, AbstractDreamer said:

So if we removed all massive things from universe, do the physics of spacetime have any relevance?

Yes. Models of spacetime with no mass are useful for understanding GR.

8 minutes ago, AbstractDreamer said:

If we removed or changed the physics of spacetime, would that affect the nature of any massless things?

Probably. One definition of mass is "the curvature it causes in spacetime". If you change that then perhaps you are changing the meaning or effect of mass. But, again, once you start departing from the physics we know then any answers are just guesses.

10 minutes ago, AbstractDreamer said:

Is spacetime a prerequisite for massive or massless things to exist?

I would say the existence of space is a requirement for anything to exist.

11 minutes ago, AbstractDreamer said:

Do massless things have any non-spacetime properties?

Momentum. Energy. Color (in the case of gluons).

Interestingly, there are no massless particles with charge. I don't know if there is an explanation for that.

13 minutes ago, AbstractDreamer said:

Do massive bosons have a gravitation effect?

Yes. So do massless ones because they have energy. (Mass does not appear in the equations for gravity; only energy.)

13 minutes ago, AbstractDreamer said:

If spacetime is a continuum and gravity curves spacetime, why is spacetimegravity not a continuum?

Gravity does not curve spacetime, energy does. Gravity is just how we perceive the curvature.

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Posted (edited)
1 hour ago, joigus said:

then is waveLENGTH a massive property too?

When a particle is massive, wavelength has to do with mass by De Broglie's relation,

$p=mv=\frac{h}{\lambda}$

p is called 'momentum.' m is the particle's mass, v is the particle's velocity, \lambda is the wavelength and h is Planck's constant.

For photons though, it's also,

$p=\frac{h}{\lambda}$

But expressing p as mv is no longer valid. So the photon's wavelength has nothing to do with its mass.

Edited by joigus
edit eq.

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