B Is a Universe Without Mass and Energy Possible?

[alan123hk]

Is it possible to have a universe with only space and time but no mass ?

I ask this question because a friend told me that time is an illusion. In fact, time does not exist. Because of the existence of matter, time can be felt through the movement of matter. If matter does not exist, time does not exist, I guess he means matter is the most basic existence.

Thanks in advance for your help.

 

[PeterDonis]

Is it possible to have a universe with only space and time but no mass ?

In the context of relativity, yes: flat Minkowski spacetime, which has space and time but no matter or energy anywhere, is a valid solution of the Einstein Field Equation.

I ask this question because a friend told me that time is an illusion. In fact, time does not exist. Because of the existence of matter, time can be felt through the movement of matter. If matter does not exist, time does not exist.

You should ask your friend what theory of physics he is using to justify his claim. I suspect his response will be a deer in the headlights look.

 

[phinds]

time is an illusion

I'll get back to you on that later.

 

[alan123hk]

In the context of relativity, yes: flat Minkowski spacetime, which has space and time but no matter or energy anywhere, is a valid solution of the Einstein Field Equation.

Thanks for your reply and valuable information.
My friend is a liberal arts student. He likes to study philosophy and religion, but knows nothing about science. Even though I know a little about the basics of science, I still don't know how to respond to him.

 

[PeterDonis]

My friend is a liberal arts student. He likes to study philosophy and religion, but knows nothing about science.

Then why does he think his claims about science have any chance of being right?

Even though I know a little about the basics of science, I still don't know how to respond to him.

Ask him why he thinks he can even have an opinion about a scientific claim when he knows nothing about science. Would he just sit there calmly, not knowing how to respond, if you expressed an opinion that he knew was wrong about philosophy or religion? And if you said you didn't know anything about philosophy or religion, would he be stumped about how to explain to you that maybe you should learn something about them first before expressing opinions?

 

[DaveC426913]

What is claimed without evidence can be dismissed with evidence.

But really, time can be detected via transmission of EMR. No matter needed.

Ask your friend if he'd like to amend his assertion.

 

[alan123hk]

Then why does he think his claims about science have any chance of being right?

Time can be felt through emission and arruval of EMR. No matter needed.
Ask your friend what he thinks.

I understand.
My own feeling is that this is very common now, just like youtube has many such channels, they mainly discuss topics such as religion, prehistoric civilization, supernatural phenomena and some unproven mysteries, in these channels, they often use their own way of thinking to interpret time, space, and matter. Although most of their explanations seem to have no basis in physics, they still fascinate the audience. Many of these audiences don't know much about physics, they just understand and agree with intuition and simple logic. This friend of mine is a fan of these YouTube channels.

 

[Herman Trivilino]

I ask this question because a friend told me that time is an illusion. In fact, time does not exist. Because of the existence of matter, time can be felt through the movement of matter. If matter does not exist, time does not exist, I guess he means matter is the most basic existence.

The devices that we use to measure time are indeed made of matter. So the question is whether or not time would exist if we had no way of measuring it.

That's a philosophical question, not physics.

The relevant philosophical question, as I see it, is whether or not time is a human invention. Time is not an illusion, and does indeed exist.

 

[DaveC426913]

The devices that we use to measure time are indeed made of matter. So the question is whether or not time would exist if we had no way of measuring it.

Being unable to measure it doesn't mean it doesn't occur.

Any photon that travels any distance will demonstrate the passage of time.

(We have to grant, in this thought experiment, that we have some way of passively peering into this universe-of-no-matter to see what's happening - without being considered part of the universe - otherwise it's an entirely moot discussion.)

 

[alan123hk]

The existence of time is an objective fact, of course it is not an illusion, I am just describing what my friend said truthfully, of course I do not agree, and immediately cited many examples to refute him. As I mentioned before My friend has no concept of physics at all.

The problem is that one of the arguments he mentions confuses me a bit. He said that time is a concept created by measuring the speed of motion of objects with mass. If mass does not exist, time will not exist. That's why I'm asking this question - Is it possible to have a universe with only space and time but no mass ?

At that time, I felt that a universe without matter and energy, but only time and space was unimaginable. I need a more in-depth answer based on physics, so I'd like to thank post 2 for the reply, which is what I was looking for.

Quote "In the context of relativity, yes: flat Minkowski spacetime, which has space and time but no matter or energy anywhere, is a valid solution of the Einstein Field Equation."

 

[PeterDonis]

He said that time is a concept created by measuring the speed of motion of objects with mass.

Again, you should ask him what theory of physics he is using to justify this claim. I've already described my expected response.

I'd like to thank post 2 for the reply, which is what I was looking for.

Note, btw, that in that post I assumed that "mass" meant "any form of matter or radiation", i.e., that it would include "massless" things like light. (The justification for this usage is that the source of gravity in GR is the stress-energy tensor, which includes both matter and radiation.) But other posters have assumed that "mass" only meant "matter", i.e., that light is not "mass", and then explained how the passage of time can be shown by the behavior of light even if no matter is present.

Both meanings of the term "mass" can be found in the physics literature, so another question you could ask your friend if you wanted to get a deer in the headlights look would be exactly what he means by "mass"--does light count as "mass" or not?

 

[DaveC426913]

Again, you should ask him what theory of physics he is using to justify this claim. I've already described my expected response.

I suspect, if he's on-the-ball, his response will be to turn the onus around, by asking ' if not for the motion of mass, how could you tell if time was passing?'

So, we might as well anticipate that and supply him with some examples.

 

[alan123hk]

So, we might as well anticipate that and supply him with some examples.

I did try to learn some concepts of special relativity myself, but I admit I don't understand general relativity at all. But it suddenly occurred to me that there is a simple explanation, please correct me if it is incorrect.

Just like an empty room, it is a vacuum and there is no matter and light in it, but the absence of matter and light in this room does not mean that there is no time. If you want to measure the passage of time in this room, you have to inject some mass or matter into it before you can measure speed and time.

If there is no time in this room, then after injecting mass, time should not be produced, because the existence of time is not created by matter.

 

[PeterDonis]

If you want to measure the passage of time in this room, you have to inject some mass or matter into it before you can measure speed and time.

If there is no time in this room, then after injecting mass, time should not be produced, because the existence of time is not created by matter.

Your reasoning rests on an implicit premise that injecting mass or matter does not change any of the physical characteristics of the room.

In relativity, the technical concept corresponding to this is a "test object"--basically an object that you can use to make measurements and find out things about the spacetime geometry, but which does not itself affect the spacetime geometry. For example, if the "universe" you want to measure is flat Minkowski spacetime, and you inject some test objects into it to observe what happens to them (and thereby show, for example, that time does exist in this universe), the test objects don't change the fact that it is flat Minkowski spacetime.

In our real universe, however, no object, strictly speaking, is an exact test object. Every object has some nonzero stress-energy and therefore makes some nonzero contribution to the spacetime geometry. So it is impossible to measure anything about an empty "room" by injecting some matter or radiation into it, without changing the spacetime geometry of the room by some amount. The best we can do is to make that amount too small for our measurements to detect in practical cases.

And that is sufficient to ground your conclusion that, if you detect the presence of time in the "room", it was there before you injected the matter into it to measure it, because "the presence of time" is an all or nothing thing: in technical language, either timelike curves exist in the spacetime geometry, or they don't. You can't take a manifold that doesn't have any timelike curves at all, and make it into a manifold that does by injecting a small amount of matter into it.

 

[haushofer]

It's a good question. The field equations of General Relativity allow an universe which is completely empty of matter and energy (these solutions can be flat, like Minkowski spacetime, or curved, like the (anti) de Sitter solutions). Spacetime is in this sense fundamental. To me, this always sounded a bit strange. There are multiple possibilities:

* GR is right in saying classical spacetime is fundamental

or

* GR is wrong, and spacetime is not fundamental

This last possibility breaks down into other possibilities:

* Classical time is not fundamental. E.g. Julian Barbour holds that time is an emergent property; his views on space are not known to me. That time is emergent sounds not that strange; what's the meaning of time in an otherwise energy/matterless universe? In this view it seems more natural that in an empty universe the spacetime degenerates to space. Interestingly, such a degeneration can also be used to describe the non-relativistic limit of General Relativity, because there space and time effectively decouple.

* Classical space is not fundamental. This is suggested by the "it from bit" -program, in which the holographic correspondence is used to argue that space emerges from entangled "atoms of space".

The possibility that OR space, OR time are not fundamental then begs the question why they can be so nicely united in General Relativity to this entity "spacetime".

 

[dsaun777]

I understand.
My own feeling is that this is very common now, just like youtube has many such channels, they mainly discuss topics such as religion, prehistoric civilization, supernatural phenomena and some unproven mysteries, in these channels, they often use their own way of thinking to interpret time, space, and matter. Although most of their explanations seem to have no basis in physics, they still fascinate the audience. Many of these audiences don't know much about physics, they just understand and agree with intuition and simple logic. This friend of mine is a fan of these YouTube channels.

Speaking of unproven supernatural phenomena and mysteries what happened to the skepticism and debunking section here?

 

[DaveC426913]

Speaking of unproven supernatural phenomena and mysteries what happened to the skepticism and debunking section here?

PF has refined their content areas to concentrate on known physics as taught in schools. Supernatural and chronological phenomena fall outside that purview.

You'll notice a correlative paucity of cranks and woo-ologists here now.

 

[dsaun777]

PF has refined their content areas to concentrate on known physics as taught in schools. Supernatural and chronological phenomena fall outside that purview.

You'll notice a correlative paucity of cranks and woo-ologists here now.

Yes, I am with you guys. But I found some of those posts entertaining. At the very least it gave smart people a means to demonstrate their debunking skills. It's like witnessing a proof being demonstrated. Our society needs debunking and skepticism now more than ever. I have never seen the world so riddled with unchecked "facts."

 

[DaveC426913]

Yes, I am with you guys. But I found some of those posts entertaining. At the very least it gave smart people a means to demonstrate their debunking skills. It's like witnessing a proof being demonstrated. Our society needs debunking and skepticism now more than ever. I have never seen the world so riddled with unchecked "facts."

Then I welcome you to sciforums.com, where wooology is alive and well and in need of reinforcements. There's a thread about UFOs that runs 7800 posts over 5 years.

 

[phinds]

I have never seen the world so riddled with unchecked "facts."

Yes, I agree, BUT ... in almost all such cases, the proponent of such "facts" has no interest in and will not listen to, any logical explanation of why they are not actually facts, so counter factual rebuttal is a waste of time.

 

[Herman Trivilino]

Although most of their explanations seem to have no basis in physics, they still fascinate the audience. Many of these audiences don't know much about physics, they just understand and agree with intuition and simple logic.

True. But keep in mind they are not thinking about the physics as deeply as you are. They simply lack the background to do so.

 

[pervect]

My $.02. I wouldn't necessarily ask the friend in question what theory of physics he was using, but rather if he was using a theory of physics, or whether he was talking philosophy. I'd rather guess the later, but it's hard to say.

If he is talking philosophy , I have two thoughts. One is to ask for some references, i.e. if he's quoting some particular philosopher. I know fairly little about philosophy except for some casual reading of the philosophy of science, so I wouldn't know.

Another thing you might try is to ask your friend if there are any particular experimental results that led him to believe time was an illusion. That might clarify what he's trying to say. Asking for experimental results is part of the philosophy of science that I mentioned, though I've forgotten the author or the exact wording of what they wrote.

 

[PeterDonis]

I wouldn't necessarily ask the friend in question what theory of physics he was using, but rather if he was using a theory of physics, or whether he was talking philosophy. I'd rather guess the later

When I said I expected the friend's response to the "what theory of physics" question to be a deer in the headlights look, this is basically what I meant. I suspect the friend never even considered the idea of looking at what theories of physics say in order to answer the question.

 

[pervect]

I am not sure of the OP is still with us, but if they are, I'd like to add a bit to my remarks about the physical meanings of time if he is. Basically, there are at least three common and slightly different ideas that are often not distinguished between that are related to time. The first idea is called "proper time" by physicisits, and it is the sort of time measured by a clock. This is what people are talking about when they say "time is what you measure with a clock". I have been unable to track down the exact soure of this quote, however.

The second concept of time is coordinate time, which is based on the idea of assigning four labels to an event - three to describe it's location, and one to describe time. I wouldn't describe coordinate time as being illlusion, per se, but it's not directly physical. It's like a map. A map is not the real territory, it's a representation of the territory. But I wouldn't generally call a map an "illusion", per se.

The third concept closely related to time is the idea of causality, of cause and effect. As I was trying, unsucsessfully, to find the origin of the remark "Time is what you measure with a clock", I stumbled across the following quote attributed to Einstein. (I don't have the original source, just that it was attributed to Einstein).

People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion.

I'm not sure I would have put things in quite the way Einstien did, but I think this may be the origin of the meme the OP was discussing.

I tend to interpret Einstein's remarks as a statement that causality in special relativity works a bit differently than it does in classical mechanics, and possibly as a statement about the much-debated philosophy of the "block universe".

But I'm sure there is room for a lot of different opinions and discussion on the mater, however it's more a matter of history and philosophy than physics.

 

[alan123hk]

Please don't blame my friend too much. As I have already said, my friend does not even have the most basic concepts of physics, nor has he formally studied philosophy. In fact, I think there are many such people in this world. Their emotional intelligence is well developed, and they like literature, art and music, but their logical reasoning ability is relatively weak. Different people in this world have different hobbies and areas of expertise, although there are also people who are good at all areas.

For those who have no interest and talent in science, they will also be curious about this universe and have many questions, such as how the universe was born, what is time and space, whether there is reincarnation, etc. Since they are not interested or gifted at physics, they do not seek answers in this way. So they are sometimes influenced by a large number of these channels on youtube, and while these youtube channels send messages that often have no scientific basis or even violate scientific principles, unfortunately to them often seem very convincing and reasonable .

But because my friend often discusses problems with me, he may be influenced by me, so sometimes he will ask some difficult questions. He said that since time is the measure of the movement of matter or energy from one point in space to another, time is illusory and and cannot be seen directly with the naked eye. Time doesn't exist when matter doesn't exist.

I'm a bit overwhelmed by his question, so I'm asking on this forum if it's possible to have a universe without mass and energy, just time and space, from the perspective of general relativity.

This true story is as simple as that.

 

[PeterDonis]

I'm asking on this forum if it's possible to have a universe without mass and energy, just time and space, from the perspective of general relativity.

Asked and answered.

Thread closed.