Can Physics Answer the Five Night-Time Questions of the Universe?

[marcus]

Sabine Hossenfelder posted these questions 21 Nov on her blog.
http://backreaction.blogspot.com/2013/11/the-five-questions-that-keep-physicists.html They are too good not to copy here for us at Beyond forum. I've been a Bee fan for a long time--admire her commonsense insight into essentials. I'll just copy the questions--you should read the whole post, if you haven't already.
==quote from Bee's post==

Is the time-evolution of the universe deterministic, indeterministic or neither?

How can we find out? Can we at all? And, based on this, is free will an illusion? This question doesn’t really fall into any particular research area in physics as it concerns the way we formulate the laws of nature in general. It is probably closest to the foundations of quantum mechanics, or at least that’s where it gets most sympathy.

Does the past exist in the same way as the present? Does the future?

Does a younger version of yourself still exist, just that you’re not able to communicate with him (her), or is there something special about the present moment? The relevance of this question (as Lee elaborated on in his recent book) stems from the fact that none of our present descriptions of nature assigns any special property to the ever-changing present. I would argue this question is closest to quantum gravity since it can’t be addressed without knowing what space and time fundamentally are.

Is mathematics the best way to model nature? Are there systems that cannot be described by mathematics?

I blame Max Tegmark for this question. I’m not a Platonist and don’t believe that nature ultimately is mathematics. I don’t believe this because it doesn’t seem likely that the description of nature that humans discovered just yesterday would be the ultimate one. But if it’s not then what is the difference between mathematics and reality? Is there anything better? If so, what? If not, what does this mean for science?

Does a theory of everything exist and can it be used, in practice (!), to derive the laws of nature for all emergent quantities?

If so, will science come to an end? If not, are there properties of nature that cannot be understood or even modeled by any conscious being? Are there cases of strong emergence? Can we use science to understand the evolution of life, the development of complex systems, and will we be able to tell how consciousness will develop from here on?

What is the origin and fate of the universe and does it depend on the existence of other universes?

That’s the question from my list you are most likely to find on any ‘big questions of physics’ list. It lies on the intersection of cosmology and quantum gravity. Dark matter, dark energy, black holes, inflation and eternal inflation, the nature and existence of space-time singularities all play a role to understand the evolution of the universe.
==endquote==

She calls these the "night-time questions" because they are not the practical well-defined sort that are part of a physicists ordinary daytime job (like "what particle constitutes dark matter?"). Instead they are the questions that could keep a physicist awake at night worrying about them. What's the right way to even ask such questions, much less answer them?

 

[phinds]

Very interesting. Thanks for posting.

 

[marcus]

Very interesting. Thanks for posting.

You are welcome! I'm glad you liked some of the questions. I'm not wild about the last two ("final" theory and "multi-"verse) personally. I think the universe is what is around us and influences what we experience and what we want to explain. It is not our job to make up additional complications which do not influence what we experience and which we don't need for explaining and predicting what we experience. An infinitude of irrelevant possibilities, a "so what?-"iverse.

And I take for granted that there is no final theory just as there is no final human language and no final human language of mathematics. A theory is a human-made mathematical-language construct.
There are several ways to see that the process of explanation can always continue. No explanation can contain an explanation of why it is correct. No model tells us why it is the correct model.

So it is Hossenfelder's first THREE that intrigue me. But other people can have different favorites.

BTW did you see that the recent Fuchs Mermin Schack paper channels earlier papers by Rovelli but does not cite them?!
The Quantum Bayes paper ("QBism" I guess pronounced "cubism") 1311.5253

 

[friend]

...
There are several ways to see that the process of explanation can always continue. No explanation can contain an explanation of why it is correct. No model tells us why it is the correct model.

So it is Hossenfelder's first THREE that intrigue me.

Actually, if we ever found a theory of everything, it would by definition explain all the rest of these questions.

 

[phinds]

You are welcome! I'm glad you liked some of the questions. I'm not wild about the last two ("final" theory and "multi-"verse) personally. I think the universe is what is around us and influences what we experience and what we want to explain. It is not our job to make up additional complications which do not influence what we experience and which we don't need for explaining and predicting what we experience. An infinitude of irrelevant possibilities, a "so what?-"iverse.

I could not agree more.

 

[strangerep]

Sabine Hossenfelder posted these questions 21 Nov on her blog.

I'm reading them now, cheers.

I've been a Bee fan for a long time--admire her commonsense insight into essentials.

Me too, but... have you noticed the gradually increasing levels of stress, audible in her tone sometimes, that seem to have been getting louder over the past few years as the realities of motherhood take their toll? Or is that just my imagination?

 

[TumblingDice]

I started reading Bee's blog a little over a year ago, about a month before I began reading (lurking at) PF. I have a comment on the "mathematics modeling nature" question and hope it isn't too over-the-top. Mathematics covers a lot of ground - arithmetic, geometry, calculus, complex numbers, et al. All are abstract and many were created to model real world scenarios. Even 1, 2, 3 are abstract representations of real world quantities, and we learn and 'chunk' in our brains that 1 + 2 = 3 and so on.

Is formal logic under the realm of mathematics? What about Feynman diagrams? As abstract representations that are well defined and have rules of 'operation', perhaps so.

My point is, since nature does not appear to emerge in a random fashion, wouldn't any modeling system have to fall into the realm of mathematics, even if we haven't defined the abstraction and rules yet?

 

[marcus]

I'm reading them now, cheers.

Me too, but... have you noticed the gradually increasing levels of stress, audible in her tone sometimes, that seem to have been getting louder over the past few years as the realities of motherhood take their toll? Or is that just my imagination?

Heck yes! It's like working two jobs. Responsible parenting of just one child consumes a huge chunk of a person's emotional energy and she has *twins*.
Her blog suggests to me she's interested in the growth of the mind and personality and that would cause her to devote even more to it than someone else might. I think her husband shares in it though. Just my surmise.

 

[marcus]

...
Is formal logic under the realm of mathematics? What about Feynman diagrams? As abstract representations that are well defined and have rules of 'operation', perhaps so.

My point is, since nature does not appear to emerge in a random fashion, wouldn't any modeling system have to fall into the realm of mathematics, even if we haven't defined the abstraction and rules yet?

I think mathematics is evolving and growing. Broadly defined it's a bunch of different artificial schematic languages in different stages of development. The community of mathematicians determines what belongs under the math heading and what doesn't. They decide what is interesting, what should be generalized, what should be imitated, and what is merely a special case of some other what.

I'm not an authority on this. Personally I don't think it has hard and fast boundaries. Feynman diagrams? Sure.Formallogic? Sure. Maybe someone else should answer this. Someone with a tidy mind.

 

[TumblingDice]

Heck yes! It's like working two jobs. Responsible parenting of just one child consumes a huge chunk of a person's emotional energy and she has *twins*.
Her blog suggests to me she's interested in the growth of the mind and personality and that would cause her to devote even more to it than someone else might. I think her husband shares in it though. Just my surmise.

I've hoped that Bee's "Interna" postings were a great release for her energy levels with the kids and chaos in general. There a refreshing break to read as well. Know that Bee makes all posts these days, but noticed that Stefan was removed from the blog graphic. Glad to read that his tax status finally came through for the kids! Two countries and tax laws. Bet that wasn't a walk in the park.

 

[TumblingDice]

The community of mathematicians determines what belongs under the math heading and what doesn't. They decide what is interesting, what should be generalized, what should be imitated, and what is merely a special case of some other what. ... Maybe someone else should answer this. Someone with a tidy mind.

You're too funny! Well, if all well-defined abstractions that model systems using a finite set of operations and rules don't fall under the general field of mathematics (heaven forbid philosophy), maybe someone will discover a new, major branch of 'science'. ? I wonder what it could use instead of math?

 

[martinbn]

I think mathematics is evolving and growing. Broadly defined it's a bunch of different artificial schematic languages in different stages of development. The community of mathematicians determines what belongs under the math heading and what doesn't. They decide what is interesting, what should be generalized, what should be imitated, and what is merely a special case of some other what.

Which means that her question about mathematics is, from a certain point of view, meaningless. What ever it is that describes reality (and not only) will be a part of mathematics.

 

[Maui]

Is the time-evolution of the universe deterministic, indeterministic or neither?

How can we find out? Can we at all? And, based on this, is free will an illusion? This question doesn’t really fall into any particular research area in physics as it concerns the way we formulate the laws of nature in general. It is probably closest to the foundations of quantum mechanics, or at least that’s where it gets most sympathy.

Indeed, it seems to appear strongest at the foundations of quantum mechanics. I have a different comment though - there is peer review research cited a dozen times that gives strong evidence that mind and free will are not illusions:

'Voluntary control of human temporal lobe neurons'

http://www.nature.com/nature/journal/v467/n7319/full/nature09510.html

(the whole paper can also be found by searching a random string of words from the article in google even without subscription)

In the study, subjects were asked to focus their attention on demand to different objects and thus voluntarily control which neurons were to be fired. This finding is incompatible with determinism since no physical process has been linked to voluntary neuron firings.

 

[atyy]

Indeed, it seems to appear strongest at the foundations of quantum mechanics. I have a different comment though - there is peer review research cited a dozen times that gives strong evidence that mind and free will are not illusions:

'Voluntary control of human temporal lobe neurons'

http://www.nature.com/nature/journal/v467/n7319/full/nature09510.html

(the whole paper can also be found by searching a random string of words from the article in google even without subscription)

In the study, subjects were asked to focus their attention on demand to different objects and thus voluntarily control which neurons were to be fired. This finding is incompatible with determinism since no physical process has been linked to voluntary neuron firings.

Your interpretation of the results is not that of the authors. Deterministic classical physics is sufficient to explain random neural firing.

 

[Maui]

Your interpretation of the results is not that of the authors. Deterministic classical physics is sufficient to explain random neural firing.

That's not what I am reading. What do you mean by 'random neural firing'?

'By providing real-time feedback of the activity of these MTL neurons on an external display, we demonstrate that subjects control the firing activity of their neurons on single trials specifically and speedily...'

For the same retinal input, the firing rate of neurons responding to the target pictures was much higher when subjects focused their attention on the target than when they focused on the distractor. The only difference was the mental state of the subject, following the instruction to suppress one or the other image.

To quantify the extent to which attention and other volitional pro-cesses dominate firing rates in the face of bottom-up sensory evokedresponses, we devised a top-down control (TDC) index. TDC quan-tifiesthelevelofcontrolthatsubjectshaveoveraspecificunitandisthedifference between the normalized firing rate when the subjectattended the unit’s preferred stimulus and the normalized rate whenthe subject attended the distractor image. That is, we subtracted thelowerfromthe uppercurveinFig.4a...

You can't quantify mind, attention, mental states, cognition and TDC with classical physics. Where do the authors claims so?The authors appear to use the words 'subject's mind' and 'the subject' interchangeably throughout the paper.

The editor's summary says it the clearest:

This work provides direct evidence that humans can control the neuronal activity of their own visual neurons deep inside their own brain, and that such activity can be decoded to control devices.

http://www.nature.com/nature/journal/v467/n7319/full/nature09510.html#/comments

It is usually assumed that neuronal activity(neurons firing) control humans(and human behavior) and the above wording implies that 'humans can control neuronal activity' means 'human minds can control neuronal activity...' otherwise you get the meaningless statement -- 'humans control humans' which is also a logical contradiction.

 

[atyy]

That's not what I am reading. What do you mean by 'random neural firing'?

'By providing real-time feedback of the activity of these MTL neurons on an external display, we demonstrate that subjects control the firing activity of their neurons on single trials specifically and speedily...'

For the same retinal input, the firing rate of neurons responding to the target pictures was much higher when subjects focused their attention on the target than when they focused on the distractor. The only difference was the mental state of the subject, following the instruction to suppress one or the other image.

To quantify the extent to which attention and other volitional pro-cesses dominate firing rates in the face of bottom-up sensory evokedresponses, we devised a top-down control (TDC) index. TDC quan-tifiesthelevelofcontrolthatsubjectshaveoveraspecificunitandisthedifference between the normalized firing rate when the subjectattended the unit’s preferred stimulus and the normalized rate whenthe subject attended the distractor image. That is, we subtracted thelowerfromthe uppercurveinFig.4a...

You can't quantify mind, attention, mental states, cognition and TDC with classical physics. Where do the authors claims so?The authors appear to use the words 'subject's mind' and 'the subject' interchangeably throughout the paper.

The editor's summary says it the clearest:

This work provides direct evidence that humans can control the neuronal activity of their own visual neurons deep inside their own brain, and that such activity can be decoded to control devices.

http://www.nature.com/nature/journal/v467/n7319/full/nature09510.html#/comments

It is usually assumed that neuronal activity(neurons firing) control humans(and human behavior) and the above wording implies that 'humans can control neuronal activity' means 'human minds can control neuronal activity...' otherwise you get the meaningless statement -- 'humans control humans' which is also a logical contradiction.

The entire paradigm is stimulus + initial state -> action.

Here the stimulus is the instruction to the person to do a certain task. Variability in the action is due to variability in the initial state.

 

[PAllen]

Which means that her question about mathematics is, from a certain point of view, meaningless. What ever it is that describes reality (and not only) will be a part of mathematics.

Hey, you beat me to this comment. I was going to 'insult' the mathematicians by saying math is a formalization and abstraction of how we see the universe behaving (with a little(:tongue:) life of its own). Therefore math will necessarily always be the best way to describe the universe unless it is altogether indescribable.

 

[Ilja]

I do not think these questions are in some sense smart.

Of course, the question is what is a smart question. I would name a question smart, if searching for an answer leads, almost automatically, to some unexpected interesting results.

The archetypical example of a smart question would be cui bono, to whose benefit. Instead of thinking about who has done something, you think about something slightly different. The results, then, will usually influence your answers to the question who has done it. So, you will often reach some progress in solving the really important question by solving, at first, the smart question.

I cannot identify anything in the proposed questions which would make them "smart" in this sense. There is no good idea how to answer them. There is no reason to believe that one or another answer to this question can be helpful in solving really interesting questions like what is the next more fundamental theory beyond the standard model or beyond quantum theory or general relativity.

One can be easily answered: We can never be sure if the universe is deterministic or random. Why? We can never be sure that we have found the most fundamental theory. We know examples where the character changes if we move toward a more fundamental theory. From deterministic to random: Thermodynamics/fluid dynamics (a deterministic field theory) -> kinetic theory, Maxwell theory -> QED. In the other direction: Deterministic chaos -> underlying deterministic theory, quantum theory -> de Broglie-Bohm. Is the answer helpful? Not at all.

 

[Maui]

The entire paradigm is stimulus + initial state -> action.

Here the stimulus is the instruction to the person to do a certain task. Variability in the action is due to variability in the initial state.

The stimulus was not physical. If you actually return to the article, they had the subjects look at the same image(same number of photons landed at their retinas) but were asked to shift their attention and see the 2nd image similar to this:

http://eternitycafe.blogspot.com/2009/12/do-you-see-what-i-see.html

By changing their focus on demand, subjects were able to activate different set of their neurons.

This stimulus is not physical as nothing physical changed in the setup. It's in no way similar to giving an injection, removing tissue, taking a pill or stimulating physically an organ of the human body. The stimulus is purely mental and this is the gist of the experiment.

 

[atyy]

The stimulus was not physical. If you actually return to the article, they had the subjects look at the same image(same number of photons landed at their retinas) but were asked to shift their attention and see the 2nd image similar to this:

http://eternitycafe.blogspot.com/2009/12/do-you-see-what-i-see.html

By changing their focus on demand, subjects were able to activate different set of their neurons.

This stimulus is not physical as nothing physical changed in the setup. It's in no way similar to giving an injection, removing tissue, taking a pill or stimulating physically an organ of the human body. The stimulus is purely mental and this is the gist of the experiment.

The instructions to the subjects to do a different task with the same image were physical.

http://eternitycafe.blogspot.com/2009/12/do-you-see-what-i-see.html.

In specific instances where the same image causes different outcomes, we do not always know the specific explanation in each case. However, we do have candidate classical deterministic mechanisms. Take a look, for example, at Bryant and Segundo's http://www.ncbi.nlm.nih.gov/pubmed/978519 (free links to the paper at the top right). In Bryant and Segundo's Fig. 4, they show the neuron's response to what they consider identical injections of current. Because of the identical current injections, the neuron's response is almost identical from trial to trial. Yet, as the arrow indicates, at a particular point in the stimulus, the neuron responded differently from trial to trial. These are neurons in a sea slug. What explanation would you suggest?

Another interesting place to look is Fellous, Tiesinga, Thomas and Sejnowski's http://www.ncbi.nlm.nih.gov/pubmed/15044538 . Fellous, Tiesinga, Thomas and Sejnowski's Fig. 2 shows more examples of neurons responding differently to currents that are identical to within their experimental resolution. These are neurons in a dish. What explanation would you suggest?

 

[Pythagorean]

Is the time-evolution of the universe deterministic, indeterministic or neither?

How can we find out? Can we at all? And, based on this, is free will an illusion? This question doesn’t really fall into any particular research area in physics as it concerns the way we formulate the laws of nature in general. It is probably closest to the foundations of quantum mechanics, or at least that’s where it gets most sympathy.

Neither. Without the neither option, I think this is a wrong question. Deterministic/indeterministic are concepts we use to discuss how trajectories behave in phase space. It allows us to construct models in meaningful ways and make assumptions about them. Determinism is especially great for this because trajectories in phase space can't intersect, which makes phase diagrams easier to extrapolate once you've found something like a homoclinic (or heteroclinic) orbit. If trajectories can intersect, you lose a lot of predictive power (I guess that's not surprising that more random systems are harder to predict).

But I think the expression "the map is not the territory" fits here.

The more scientifically relevant question would be specific to particular phenomena: is this phenomena best described by a deterministic model or a stochastic one?

Furthermore, we often use stochastic modelling to simplify exceedingly complex deterministic systems. If you have 10000 of particles that are all the same, you might prefer to describe their ensemble behavior statistically since it would greatly reduce the complexity of any mathematical expression of the system (by orders of magnitude). So using one kind of model isn't always indicative of the behavior of itself, only of our choice of simplification.

 

[bahamagreen]

Rumor has it that if P = NP then the answers to all questions are possible...?

 

[Fra]

I've been running really low in time for a long time, everyday stuff just takes too much time, but I popped in here to browse some posts. I bought the smolin/unger book some year ago but it's still sitting outouched due to lack of time.

Does the past exist in the same way as the present? Does the future?

Does a younger version of yourself still exist, just that you’re not able to communicate with him (her), or is there something special about the present moment? The relevance of this question (as Lee elaborated on in his recent book) stems from the fact that none of our present descriptions of nature assigns any special property to the ever-changing present. I would argue this question is closest to quantum gravity since it can’t be addressed without knowing what space and time fundamentally are.

Is mathematics the best way to model nature? Are there systems that cannot be described by mathematics?

The way I see it, is that the past depends on the present in the sense that it exists IN the present. But only as remnants. This is all there is. The "actual past" whatever it is, I don't believe in since to the stretch of my mind at least - no observer can possibly encode and hold so much information in any realizable way that is meaningful. So the past is IMO necessarily and unavoidable ereased, YET it lives on since it seeded the present.

I'm no tegemark fan either, I think of "mathematics" as the language we humans necessarily need in order to produce computable predictions. Although in theory one can imagine say hitchhiker's guide style "computing devices", that are nothing but an evolving subsystem, but we are human scientist and we need a mathematical to implement as computable models. No using computers human sciences are unlikely ot make progress. So I see mathematics and logic (without worrying about exact classifications) as the necessary languange for a human scientist but in no way "magical".

/Fredrik

 

[ChrisVer]

although the thread is actually philosophical...
I have to say that I don't believe in a deterministic time. I mean if time flow was deterministic, then we could move backwards in it without a problem. However, CP violation should imply a T violation, and thus going backwards in time can't be so "deterministic" as it seems...
What do you think?

 

[marcus]

Since we've turned a page I'll bring forward the "five questions that keep physicists awake at night" that Sabine Hossenfelder posted 21 Nov on her blog.
http://backreaction.blogspot.com/2013/11/the-five-questions-that-keep-physicists.html I've been a Bee fan for a long time--admire her commonsense insight into essentials. I'll just copy the questions--but recommend that anyone who hasn't already done so read the whole post.
==quote from Bee's post==

Is the time-evolution of the universe deterministic, indeterministic or neither?

How can we find out? Can we at all? And, based on this, is free will an illusion? This question doesn’t really fall into any particular research area in physics as it concerns the way we formulate the laws of nature in general. It is probably closest to the foundations of quantum mechanics, or at least that’s where it gets most sympathy.

Does the past exist in the same way as the present? Does the future?

Does a younger version of yourself still exist, just that you’re not able to communicate with him (her), or is there something special about the present moment? The relevance of this question (as Lee elaborated on in his recent book) stems from the fact that none of our present descriptions of nature assigns any special property to the ever-changing present. I would argue this question is closest to quantum gravity since it can’t be addressed without knowing what space and time fundamentally are.

Is mathematics the best way to model nature? Are there systems that cannot be described by mathematics?

I blame Max Tegmark for this question. I’m not a Platonist and don’t believe that nature ultimately is mathematics. I don’t believe this because it doesn’t seem likely that the description of nature that humans discovered just yesterday would be the ultimate one. But if it’s not then what is the difference between mathematics and reality? Is there anything better? If so, what? If not, what does this mean for science?

Does a theory of everything exist and can it be used, in practice (!), to derive the laws of nature for all emergent quantities?

If so, will science come to an end? If not, are there properties of nature that cannot be understood or even modeled by any conscious being? Are there cases of strong emergence? Can we use science to understand the evolution of life, the development of complex systems, and will we be able to tell how consciousness will develop from here on?

What is the origin and fate of the universe and does it depend on the existence of other universes?

That’s the question from my list you are most likely to find on any ‘big questions of physics’ list. It lies on the intersection of cosmology and quantum gravity. Dark matter, dark energy, black holes, inflation and eternal inflation, the nature and existence of space-time singularities all play a role to understand the evolution of the universe.
==endquote==

If these questions (at least for the most part) come within the purview of Physics, and can be addressed by physicists, then we can discuss them in this forum.

I tend to think they are questions that physicists (using common sense and the evolving tools of their trade) can be expected to answer for themselves.

Some of them IMHO have obvious answers. E.g. math is an evolving artificial language. Mathematicians INVENT concepts rules methods where they detect the need for them. It is not a fixed thing. So one cannot say that it is inadequate for doing physics. Where limits are encountered, the language will be extended.

And of course there can be no final explanation. Science will not "come to an end". Every explanation begs the next question---explain the grounds of THAT explanation.

Let's avoid philosophizing about terminology categories concepts and focus on those of Bee's questions where we can see a clear physics content.