Szydagis' point 3: Interstellar travel is too hard

[Rick Robson]

"... would be thrilled if we would find some way of talking about all of standard physics, not just the toy models that we're looking at, but all the standard physics in a way that doesn't put spacetime in and doesn't put quantum mechanics in, and gets the answers out. And ultimately then, if we really understand it, then we'll have the beginning of an understanding, a starting point, from which we can see the emergence of spacetime and quantum mechanics

Fascinating. I wonder though how that undoubtedly interesting theory dealt with the reality experimentally proved by the Nobel Prize winners Alan Aspect, John Clauser y Anton Zeilinger that the classic laws of Standard Physics present clear flaws when it comes to determine the full way Nature behaves, in such a way that one definitely CAN'T get the answers out by NOT putting in quantum mechanics.

 

[FatPhil]

Fascinating. I wonder though how that undoubtedly interesting theory dealt with the reality experimentally proved by the Nobel Prize winners Alan Aspect, John Clauser y Anton Zeilinger that the classic laws of Standard Physics present clear flaws when it comes to determine the full way Nature behaves, in such a way that one definitely CAN'T get the answers out by NOT putting in quantum mechanics.

One of us has misunderstood @LilWabbit. I see the bit you quoted as saying that if you can derive QM from it, then you don't need to put QM into it.

 

[qed]

Nothing prevents us from building a particle accelerator in space, and accellerating massive objects (such atomic nuclei), very close to the speed of light.
I'm not sure I understand your question, your stack-overflow link which violates the no-click policy shows a mistaken point of view being corrected, but what you appear to have asked is countered by my response. ANy CRT monitor in any space mission was a primitive particle accelerator that would almost certainly have beamed particles at relativistic speed (it depends on the voltage, obviously, but 0.01c is trivial, and 0.1c is possible).

Whether a body can accelerate *itself* (in contrast to "an object" above) to relativistic speeds is probably the question you were looking for an answer to, and that's been answered here and on SE.

I agree. I did mean with fuel self contained with capsule. But I have done some initial calculations, and it appears possible. So I retract.

[... I am trying to calculating the mass of the fuel to get capsule of mass m to pc, p being percent ...]

 

[MyMatesBrainwashed]

This point about time and distance that he makes really smells of getting tied up in the details and missing the picture.

I'm fairly certain that his actual rebuttal to vast distances and times is that it doesn't matter. It's essentially that send something travelling in space and given enough time it will travel a distance. As long as there's enough time in the past for something to have travelled a distance then there's the possibility that something has travelled that distance. Yes, the distances are vast but there's enough time for them to be travelled. That's it.

There's no point getting bogged down in % of c because even he says that argument is moot (just use a computer instead).

But I don't think that's the real issue with distance and time. Like sure, I could travel to Andromeda and be alive (given his maths but I do wonder what decelerating does to the dilation), but there's every chance I could be the last human in the universe by the time I get there. I have no way of finding out if I am either. What am I doing there? What was the plan?

And if you want to subscribe to the idea that physics problems MIGHT be solved at some point then time is VERY important. You run into that whole someone else sent 1 million years after me might beat me there issue (can't remember who's to credit for that paradox idea but I do like it).

 

[Ann K]

And if you want to subscribe to the idea that physics problems MIGHT be solved at some point then time is VERY important.

His faith in the "we'll solve it some day" solution smacks of "turning base metal into gold".

 

[FatPhil]

His faith in the "we'll solve it some day" solution smacks of "turning base metal into gold".

Not necessarily a great example - you can bombard lead in a particle acceperator and get gold. Then again, the yield's terrible for the cost, and perhaps that's a feature that future theoretical tech might also suffer from too, so it might be a great example! (Not knowing the future tech, or its cost, makes that undecidable as yet.)

 

[Mendel]

Not necessarily a great example

it's a reference to the Philosopher's Stone

Article:

The philosopher's stone or more properly philosophers' stone (Arabic: ḥajar al-falāsifa, Latin: lapis philosophorum), is a mythic alchemical substance capable of turning base metals such as mercury into gold (chrysopoeia, from the Greek χρυσός khrusos, "gold", and ποιεῖν poiēin, "to make") or silver. It is also called the elixir of life, useful for rejuvenation and for achieving immortality;[1] for many centuries, it was the most sought goal in alchemy.

Source: https://en.m.wikipedia.org/wiki/Philosopher%27s_stone

Except for an unproven theory about ancient electroplating (discussed elsewhere on Metabunk), this alchemical marvel was always thought possible, but never was—just like interstellar/intergalactic travel might be.

 

[LilWabbit]

This thread got me to thinking. I've been trying to put my finger on the exact nature of the problem that I've felt seriously plagues the standard ufological argument which reads roughly along these lines:

'The superior intelligence of aliens and interdimensional beings can surely explain the performance of feats that, for us, seem to violate our limited understanding of physical laws.'

This argument is not entirely without logical merit. But it entails a problem that I've 'felt' as intuitively compelling but haven't really had an opportunity to analyze more seriously. So here goes.

(1) Whatever is describable using man-made physical categories and predicates -- such as 'beings with bodies', 'spacecraft', 'form', 'shape', 'motion', 'light', 'intelligence', 'dimension', 'spacetime', 'matter', 'gravity', 'mass', 'negative', 'positive', 'quantity', 'energy', 'force', 'power', 'heat', 'consciousness', 'propulsion', and even the notion of 'existence' itself -- is humanly knowable at least to the extent of these categories.

(2) If we are to accept these humanly known physical categories in our description of aliens, it would be intellectually dishonest and logically problematic not to accept, by the same token, the humanly known physical laws applicable to the mentioned categories.

(3) But if we still choose not to, then the self-same intellectual honesty and logic dictates we must also cease to refer to these beings, their crafts and their behaviours by means of any known physical categories.

(4) Otherwise we're merely moving goal-posts to avoid reasoned critique, and using physical categories selectively to the extent they serve us while ceasing to use them when they get us in trouble with real science.

All of science fiction uses known physical categories, which is perfectly acceptable. That's why we call it science fiction. We just don't pretend it's science fact.

 

[Ann K]

2) If we are to accept these humanly known physical categories in our description of aliens, it would be intellectually dishonest and logically problematic not to accept, by the same token, the humanly known physical laws applicable to the mentioned categories.

(3) But if we still choose not to, then the self-same intellectual honesty and logic dictates we must also cease to refer to these beings, their crafts and their behaviours by means of any known physical categories.

I agree with most of your post, but I think we lack the vocabulary to discuss the subject at all without falling back upon known terms and categories, don't we? How can any description of phenomena be transmitted to another person without describing them in terms that are familiar to both? Intellectual honesty, I agree with, but a change in vocabulary is window-dressing that would just muddy the waters.

 

[Mendel]

(2) If we are to accept these humanly known physical categories in our description of aliens, it would be intellectually dishonest and logically problematic not to accept, by the same token, the humanly known physical laws applicable to the mentioned categories.

You seem to never have read a fantasy novel?

All of science fiction uses known physical categories, which is perfectly acceptable.

Such as Light Sabers. We know what they do, even though it's impossible for them to do it. There is no known physics to describe what they do. There is no "humanly known physical law" that applies to them even though they're perfectly described in common terms: a sword with a blade made of light.

'The superior intelligence of aliens and interdimensional beings can surely explain the performance of feats that, for us, seem to violate our limited understanding of physical laws.'

Could we do this with time travel? Find one thing or three that is possible now, that an educated person at a certain point in the past would have considered absolutely impossible (such as a perpetuum mobile)?

Because I'm not at all convinced that this reasoning has merit.

 

[LilWabbit]

I agree with most of your post, but I think we lack the vocabulary to discuss the subject at all without falling back upon known terms and categories, don't we?

Indeed, but the point is the selective usage of physics vocabulary when it suits the narrative and happily withdrawing into science fiction when actual physics starts creating problems for the narrative.

For example, the ufologist will claim a spacecraft is featured in a UAP video as a radar return, moving 24 kilometers in one second, starting and ending with zero speed. He also accepts that craft has 'mass' and appears as a 'radar return'. Then, by the same token, he should accept that such a craft, in order to perform such a feat, must generate a superhot fireball and a sonic boom audible at a great distance from the craft far exceeding the radar horizon. But since the only physical track the craft leaves is a radar return, the ufologist withdraws into science fiction to explain away the absence of other necessary measurement outcomes of such a fast-moving object with a mass. If he can explain them away by a rigorous scientific argument that's testable, then we'd be on the cusp of learning something new and should happily welcome his analysis.

I like Mendel's lightsaber analogy. A 'Lightsaber Believer' (LB) will just shrug off the physics-defying bit of the saber by appeal to 'superior intelligence/technology' whilst he is more than happy to accept many other physical properties applying to the lightsaber. The debunker would be happy if the LB would either (1) claim the whole lightsaber in its entirety is some astral non-physical 'object' (in which case we bypass science altogether and agree to end the conversation right there) or (2) honestly accept lightsabers are just science fiction which is sometimes fun to indulge in. But the LB does neither and insists the lightsaber is a scientific fact. Hence the problem articulated in my 4 points earlier.

To recap, you can't involve physics in a serious scientific claim while being conveniently selective about how it applies and to what extent.

 

[LilWabbit]

Let me be clearer and formulate the Ufologistic Fallacy, which is related to the idea of advanced technology being indistinguishable from magic:

The Ufologistic Fallacy

Superintelligence implies supernatural powers.

The Problem: The assumption of an existence of a superintelligent natural being does not logically imply a supernatural being.

Hypothetically, a superintelligent natural being is a creature of our universe, part of the same natural order of things as we are and similarly subject to its fundamental constraints. Hypothetically, a supernatural being is above the natural order of things and able to avoid or manipulate its fundamental constraints.

Resolution of the Fallacy: The ufologist restricts the discussion to a superintelligent natural being which allows us to carry on a rational and scientific dialogue on the basis of scientifically testable physical laws, constants and theories. Or the ufologist accepts these beings as supernatural which allows us to stop all scientific dialogue in its tracks, and thereby saving us from getting caught up in pointless belief-based speculations.

 

[FatPhil]

To recap, you can't involve physics in a serious scientific claim while being conveniently selective about how it applies and to what extent.

I think I'd frame my view more as:
If you're introducing something that trashes our current understanding of the laws of physics, there's no merit in identifying properties that are in agreement with our current, but now trashed, understanding of the laws of physics.

More briefly: You don't get to trash the laws and still use them.

 

[Mendel]

More briefly: You don't get to trash the laws and still use them

Dark matter/dark energy don't follow the known laws of physics, although their effects can be described in terms of known physics—that's how we know they exist.

The "either all of physics, or none of it" approach is not fruitful for discovery.

 

[LilWabbit]

Dark matter/dark energy don't follow the known laws of physics,

Do you realize what you just claimed? Now, please specify which known laws of physics dark matter/dark energy do not follow?

You said "the" which implies all of them. The onus is on you to now demonstrate how dark energy doesn't follow for instance the law of conservation of energy or the various laws axiomatized in general relativity which the hypothesis of dark energy employs?

although their effects can be described in terms of known physics—that's how we know they exist.

We don't. Dark energy is a decent hypothesis but it's still only a hypothesis.

The "either all of physics, or none of it" approach is not fruitful for discovery.

How is "I will accept some physics but will ignore other bits that don't agree with my beliefs"?

 

[Ann K]

Dark matter/dark energy don't follow the known laws of physics, although their effects can be described in terms of known physics—that's how we know they exist.

All we know about what we call "dark matter" is what we imply by known physics. You're being premature in your assessment when you claim it follows some other set of laws.

 

[FatPhil]

Dark matter/dark energy don't follow the known laws of physics, although their effects can be described in terms of known physics—that's how we know they exist.

The "either all of physics, or none of it" approach is not fruitful for discovery.

Dark energy was known to Einstein, he just didn't call it that. To him it was a parameter in an equation. He later regretted it, and took it back out again, because there wasn't enough data to be sure, and so 0 the value he felt happiest with. The value of that parameter still isn't known, it still might be 0, we've not excluded that. That doesn't mean it doesn't "follow the known laws of physics".

Dark matter doesn't break the known laws of physics either at the macroscopic scale - which are the effects we are talking about. Dark matter's interaction with us is *known*, acccording to the current laws of physics, to very high accuracy, to be incredibly low. So it will never be a component of a space-ship, or an energy weapon, or a tractor beam, or a communication device, or anything that will ever interact with us at all. We might not have the first clue what dark matter is, but that doesn't mean we haven't worked out upper bounds on certain properties it must have.

If the Bogonauts from the planet Phut shoot you with their ziggawatt sterile neutrino gun - you won't even notice it.

 

[Mendel]

All we know about what we call "dark matter" is what we imply by known physics. You're being premature in your assessment when you claim it follows some other set of laws.

I'm assuming that if it followed all known physics, we'd have found it by now.

 

[FatPhil]

Do you realize what you just claimed? Now, please specify which known laws of physics dark matter/dark energy do not follow?

Dare anyone ask whether muons follow the known laws of physics?

(Spoiler: they do not, this is experimentally confirmed to "convincing" levels of certainty (over 4 sigma), however, this anomaly seems absolutely unimportant to the evolution of the universe around us.)

 

[LilWabbit]

Dare anyone ask whether muons follow the known laws of physics?

(Spoiler: they do not, this is experimentally confirmed to "convincing" levels of certainty (over 4 sigma), however, this anomaly seems absolutely unimportant to the evolution of the universe around us.)

Muons deviate from the predictions of the Standard Model of Particle Physics which is not a law but a theory.

 

[FatPhil]

Muons deviate from the predictions of the Standard Model of Particle Physics which is not a law but a theory.

I was being informal with my use of the word "law". I know philosophers have tromped into the fields of science and scattered variously both precise and simultaniously contradictory definitions of that word all over the place, so much so that it's started to become meaningless.

Pretend I said "rules" rather than "laws". I mean the things that are codified to be predictive, not mere conclusions from observations. I've never demanded that the theories of physics (Ugh - does anyone ever utter that phrase? No. They say "the laws of physics". Don't mess with both language as well as science, your inputs are not useful in either field.) be explanatory - have you really never heard the phrase "shut up and calculate" - how explanatory is that trying to be?

It looks like your semantic sophistry has even confused Steven Weinberg!

Dreams Of A Final Theory: The Search for The Fundamental Laws of Nature
Steven Weinberg
Random House, 31. aug 2010 - 272 pages

An understanding of nature's final laws may be within our grasp - a way of explaining forces and symmetries and articles that does not require further explanation. 'This starting point, to which all explanations can be traced, is what I mean by a final theory', says Steven Weinberg in this extraordinary book. In it he discusses beauty, the weakness of philosophy, the best ideas in physics and the honour of accepting a world without god.

-- https://books.google.ee/books?id=OLrZkgPsZR0C&redir_esc=y

Oh - "the weakness of philosophy" - shots fired!

 

[LilWabbit]

Pretend I said "rules" rather than "laws".

Thank you. I will take that as a grumbling concession.

Unlike theories which normally seek to provide deeper and broader explanations to observed phenomena, laws of physics (in the strictest sense) are essentially exceptionless regularities. They are universal generalizations (UG, an inference rule in predicate logic) from thousands of observations, amassed throughout the history of physics, that have repeatedly and consistently displayed certain conditionalities ('if x, then y' properties) under widely differing contexts. Over the course of time, owing to their seeming inviolability, they have become validated as 'laws'.

If, however, UG is applied simplistically, these generalizations are vulnerable to what is called 'the Johnson-Carnap continuum': (infinite) universal generalizations have zero probability.

In other words, not only is it the obvious case (taught in almost every introductory course of first-order logic) that a consistent finite number of black raven observations, no matter how numerous, does not logically follow that all future ravens observed will be black. But, in fact, having observed n black ravens, it logically follows from k successive applications of the rule of succession that the probability the next k ravens are also black approaches zero as the succession tends to infinity.

This elegant argument, however, is premised on infinite succession. It stumbles upon non-zero probabilities in actual physics, inherently associated with a finite succession of confirming observations resulting in 1 (100 % probability). Take the following formulation of the Law of Conservation of Energy as an example:

In a closed a system the total energy of the system is conserved.

This law is a logical inference from thousands upon thousands of observations whereby, invariably, 'the more closed the physical system, the more it conserves energy'. If we assume, as seems reasonable, that the universe has a finite number of systems (despite being an enormous number), then every new observation of energy-conservation being conditional upon a system's level of openness further confirms the Law of Conservation of Energy. Every single positive instance increases the probability of the law applying to future instances closer to 1. This conclusion can be made even before applying your favourite Bayesian models that add further credence to the law.

Here is a good analysis on UG and its proper application for those who wish to geek out on philosophical logic further.

Oh, "philosophy strikes right back".

 

[FatPhil]

Oh, "philosophy strikes right back".

Did you miss the post where I said Feyerabend's /Against Method/ was my toilet reading? Let's just say I'm running out of pages...

 

[Kacmarek]

Resurrecting an old thread ....

The critical aspects of energy requirements to accelerate a body (even relatively small) are definitely massive ...
Yet, the statements made that "physics thousands of years from now would still have to conform to known laws and limitations such as the first and second laws of thermodynamics" is surely fallacious

Consider that in the last 124 years or so, we have discovered ...

- Quantum nature of reality (how nature behaves at very small scales and high energies)
- Special and General Relativity - nature of gravity
- Understood how to create nuclear fission and fusion
- Understood DNA and RNA
- Understood the (current) large scale structure of space time
- Understood mechanisms like inflation (probably, not proved) explain the large scale structure of the universe
- Understood how the dinosaurs went extinct (the theory was accepted only in the 80s)

Many of these discoveries were surely about fundamental changes in the way nature/reality operates and marked a departure of human thinking for thousands of years?

Who knows what we will learn by 2124?
Some examples :

- The solution to the problem of abiogenesis
- Deeper understanding of how spacetime operates
- Unification of all fundamental forces
- Discovering what are constituents of quarks
- Experimental evidence/disproof of string theory
- Discovery of technosignatures on exoplanets

Or .... it probably will be areas completely different - things many of us cannot envision at the moment, just as (probably) even Schrodinger could not have envisioned the internet

And this is merely 2124

3124 is unimaginably far away
That, again, does not mean that the "hard" problem of interstellar travel would have been solved by then; we just dont know.

 

[John J.]

Yet, the statements made that "physics thousands of years from now would still have to conform to known laws and limitations such as the first and second laws of thermodynamics" is surely fallacious

Mmm, I sort of disagree.
The laws of thermodynamics, and the theories of relativity, are based on observed properties of the universe.
As far as we currently know, they apply everywhere.

I'd like to think that with sufficiently advanced technology humans will achieve extraordinary things, but there's no reason to believe that, say, we'll ever get more usable energy out of a system than exists in that system.

 

[MyMatesBrainwashed]

- Quantum nature of reality (how nature behaves at very small scales and high energies)
- Special and General Relativity - nature of gravity
- Understood how to create nuclear fission and fusion
- Understood DNA and RNA
- Understood the (current) large scale structure of space time
- Understood mechanisms like inflation (probably, not proved) explain the large scale structure of the universe
- Understood how the dinosaurs went extinct (the theory was accepted only in the 80s)

Many of these discoveries were surely about fundamental changes in the way nature/reality operates

None of these have broken any law of physics as we understand them.

I'm not sure that any further understanding of physics has improved the probability that they can and eventually will be broken. Possibly the opposite, I dunno. Definitely interesting.

That last sentence grates cos if nature and reality changed how it operated we wouldn't be able to improve our understanding of it.

But you could argue that saying the laws of physics will never be broken is fallacious if you really wanted to, but not based on anything we've done in the past. Just cos who knows?

 

[Kacmarek]

Mmm, I sort of disagree.
The laws of thermodynamics, and the theories of relativity, are based on observed properties of the universe.
As far as we currently know, they apply everywhere.

I'd like to think that with sufficiently advanced technology humans will achieve extraordinary things, but there's no reason to believe that, say, we'll ever get more usable energy out of a system than exists in that system.

Could I give 2 examples from "known physics"
- Did nuclear fission violate the law of conservation of energy?
- Does the theory of Cosmological Inflation violate the law of speed of light being the maximum possible? (since it resolves the horizon problem)

 

[Mauro]

Resurrecting an old thread ....

The critical aspects of energy requirements to accelerate a body (even relatively small) are definitely massive ...
Yet, the statements made that "physics thousands of years from now would still have to conform to known laws and limitations such as the first and second laws of thermodynamics" is surely fallacious

Consider that in the last 124 years or so, we have discovered ...

- Quantum nature of reality (how nature behaves at very small scales and high energies)
- Special and General Relativity - nature of gravity
- Understood how to create nuclear fission and fusion

You argument periodically resurfaces, ie.: see post #28 in this thread.

In a nutshell, the main problem with your reasoning is that you seem to think that advancements in science make more things possible, while the exact opposite is true!

If one looks at the green line (what we can actually do) it's pretty clear many more things are possible now, and the merit goes to science (and the technologies which follow). But if you look at the red line (what is theoretically possible to do) it has always gone down and down for the entire history of science.

- At the beginning (say, before 1600) people could do very little in practice, but they could think very high. There were no known barriers to
achieve any desired speed, or perpetual motion, or a perfect knowledge.
- By Newton's time things had already started to go bleak: now you have to contend with masses and accelerations and forces, thus 'laws'. You could not do everything any more, only that part of 'everything' which conformed to the laws.
- By mid-1800 thermodynamics struck a devastating blow: no free energy, no perpetual motion, no getting something out of nothing. On the up side (with the help of Newton) we got the Industrial Revolution.
- By early 1900 disaster struck. Quantum theory (one of the examples you proposed), with its fundamental randomness, put a nail in the coffin to the idea one could acquire perfect knowledge (Gödel, and then the discovery of chaos put in more nails). Special relativity (another of your examples) added an universal speed limit to the already intractable problem of interstellar travel. General relativity (another of you examples) put a fundamental limit on the energy we can ever hope to harvest from a piece of matter (the famous E=mc2). Before these discoveries we could dream of extracting any amount of energy from matter to power our spaceship, while in practice we were limited to what combustion and chemistry could achieve. After this discoveries we can extract much much more energy from matter (with fission and fusion) than we could before, but we can dream no more: at most we're limited by the tyranny of E=mc2 (which, unfortunately, is not enough anymore for our spaceship).

So, if anything, it's more probable that future advancements will find new limits (as it always happened) rather than remove old ones (as never happened).

 

[Kacmarek]

You argument periodically resurfaces, ie.: see post #28 in this thread.

In a nutshell, the main problem with your reasoning is that you seem to think that advancements in science make more things possible, while the exact opposite is true!

View attachment 68666
If one looks at the green line (what we can actually do) it's pretty clear many more things are possible now, and the merit goes to science (and the technologies which follow). But if you look at the red line (what is theoretically possible to do) it has always gone down and down for the entire history of science.

- At the beginning (say, before 1600) people could do very little in practice, but they could think very high. There were no known barriers to
achieve any desired speed, or perpetual motion, or a perfect knowledge.
- By Newton's time things had already started to go bleak: now you have to contend with masses and accelerations and forces, thus 'laws'. You could not do everything any more, only that part of 'everything' which conformed to the laws.
- By mid-1800 thermodynamics struck a devastating blow: no free energy, no perpetual motion, no getting something out of nothing. On the up side (with the help of Newton) we got the Industrial Revolution.
- By early 1900 disaster struck. Quantum theory (one of the examples you proposed), with its fundamental randomness, put a nail in the coffin to the idea one could acquire perfect knowledge (Gödel, and then the discovery of chaos put in more nails). Special relativity (another of your examples) added an universal speed limit to the already intractable problem of interstellar travel. General relativity (another of you examples) put a fundamental limit on the energy we can ever hope to harvest from a piece of matter (the famous E=mc2). Before these discoveries we could dream of extracting any amount of energy from matter to power our spaceship, while in practice we were limited to what combustion and chemistry could achieve. After this discoveries we can extract much much more energy from matter (with fission and fusion) than we could before, but we can dream no more: at most we're limited by the tyranny of E=mc2 (which, unfortunately, is not enough anymore for our spaceship).

So, if anything, it's more probable that future advancements will find new limits (as it always happened) rather than remove old ones (as never happened).

Fair points, but I would state that :

- Inflation has posited (there is some experimental evidence) that "something" (not particles) can move faster than light - space itself in the initial 10^(-33) secs after the big bang

- The discovery/invention of fission proves that one can generate energy far beyond what one would have thought even in 1900, just by splitting an atom (due to E = mc^2 principle)


Nature keeps coming up with suprises and (our understanding of) physics evolves ...

The view that the "iron law" of enormous energy required for interstellar travel is dedinitely unsolvable as of now

May not be so intractable 100 tears from now as we find new energy sources

 

[Ann K]

May not be so intractable 100 tears from now as we find new energy sources

But "new sources", of course, do not mean that energy can be used to overcome the energy requirements for interstellar travel.

 

[Kacmarek]

But "new sources", of course, do not mean that energy can be used to overcome the energy requirements for interstellar travel.

Not to be argumentative, but is it fwasible that a physical process is found that can extract energy in a new and different way from nature - the way nuclear fission/fusion did?
Engineering challenges may be huge, but solvable over time

Similarly, human evolution is say 60,000 years old, but we have discovered E = mc^2 only in the last 110-115 years
Is it not possible that a similar "reorientation" of energy laws is discovered in the next 100 or 200 years as we understand more about nature?

 

[Mauro]

Fair points, but I would state that :

- Inflation has posited (there is some experimental evidence) that "something" (not particles) can move faster than light - space itself in the initial 10^(-33) secs after the big bang

There are lots of things which move faster than light. Space can expand faster than lightspeed even now, not only at the time of inflation. Quantum-entanglement interactions (Einstein's 'spooky action at distance') even propagate at infinite speed. More down-to-earth, already in the late 1800 physics knew the 'phase speed' of an electromagnetic wave in a cavity (a metal tube) exceeds the speed of light.

The problem is that special relativity does not forbid a speed to always be lower than light's, rather it forbids information to be moved at a speed higher than c (and 'information' includes human beings and spaceships). Space expanding faster than c cannot transmit information faster than c. Quantum-entanglement collapse travels at infinite speed but cannot transmit information at all. The same goes for the phase speed in a radio-frequency cavity: it cannot transmit any information at all (one needs to use the 'group speed', which is always lower than c).

- The discovery/invention of fission proves that one can generate energy far beyond what one would have thought even in 1900, just by splitting an atom (due to E = mc^2 principle)

Not at all. It proves one can generate energy far beyond what people in 1900 could actually do. At the time physics knew of no obstacles in extracting, say, E=mc cubed or E = mc at the 8th-power or even E= m*infinite. One could dream of fully converting a piece of mass into energy and get so much to be able to accelerate a spaceship to relativistic speed. Today we know we're limited to E=mc2, and as enormous this energy is, it's not enough for a self-powered spaceship.

Nature keeps coming up with suprises and (our understanding of) physics evolves ...

Indeed, but unfortunately all those surprises have turned up bad for dreaming (the red curve), but luckily also very good for actually doing (the green curve). Don't look only at the green curve, look at the red one too!

The view that the "iron law" of enormous energy required for interstellar travel is dedinitely unsolvable as of now

May not be so intractable 100 tears from now as we find new energy sources

'May', yes: everything which is not logically forbidden is possible. But this does not mean it's probable, with all the history of science pointing firmly towards 'not probable at all' (rather, the contrary).

I know this is hard to accept, it was difficult for me too, very difficult, but that's what reality is. It was like throwing the One Ring in the Cracks of Doom, renouncing a limitless but unattainable power to accept the reality of human life, and its limits, and its actual possibilities. Not easy at all, but it made me grow.

 

[Kacmarek]

There are lots of things which move faster than light. Space can expand faster than lightspeed even now, not only at the time of inflation. Quantum-entanglement interactions (Einstein's 'spooky action at distance') even propagate at infinite speed. More down-to-earth, already in the late 1800 physics knew the 'phase speed' of an electromagnetic wave in a cavity (a metal tube) exceeds the speed of light.

The problem is that special relativity does not forbid a speed to always be lower than light's, rather it forbids information to be moved at a speed higher than c (and 'information' includes human beings and spaceships). Space expanding faster than c cannot transmit information faster than c. Quantum-entanglement collapse travels at infinite speed but cannot transmit information at all. The same goes for the phase speed in a radio-frequency cavity: it cannot transmit any information at all (one needs to use the 'group speed', which is always lower than c).


Not at all. It proves one can generate energy far beyond what people in 1900 could actually do. At the time physics knew of no obstacles in extracting, say, E=mc cubed or E = mc at the 8th-power or even E= m*infinite. One could dream of fully converting a piece of mass into energy and get so much to be able to accelerate a spaceship to relativistic speed. Today we know we're limited to E=mc2, and as enormous this energy is, it's not enough for a self-powered spaceship.


Indeed, but unfortunately all those surprises have turned up bad for dreaming (the red curve), but luckily also very good for actually doing (the green curve). Don't look only at the green curve, look at the red one too!


'May', yes: everything which is not logically forbidden is possible. But this does not mean it's probable, with all the history of science pointing firmly towards 'not probable at all' (rather, the contrary).

I know this is hard to accept, it was difficult for me too, very difficult, but that's what reality is. It was like throwing the One Ring in the Cracks of Doom, renouncing an unattainable limitless power to accept the reality of human life and its limits. Not easy at all, but it made me grow.

Is it not possible that (like Newton's laws are special cases for SR and GR), similarly E = mc^2 is a special case for (undiscovered) laws?

Any particular reason for the limitation imposed by E = mc^2 not be superseded in the next 100 or 200 years?
(agree that no evidence so far of any violation of it )

 

[Mauro]

Is it not possible that (like Newton's laws are special cases for SR and GR), similarly E = mc^2 is a special case for (undiscovered) laws?

This is surely possible (even probable I'd say), but this has no bearing on my argument. Indeed, both SR and GR, in 'correcting' Newton, added more limits to what is possible which were previously unknown. A new theory which 'corrects' Einstein will probably do the same, as always has happened.

Any particular reason for the limitation imposed by E = mc^2 not be superseded in the next 100 or 200 years?
(agree that no evidence so far of any violation of it )

See above. General relativity is a very, very strong theory, but of course it might be superseded. And we might gain the ability to actually do something new (as always happened) but, probably, we will also discover the ceiling of what can possibly be done got even lower (as always happened).

 

[SuppaCoup]

I've followed early stage research into things like sheared-flow stabilized z-pinch fusion space propulsion with a lot of interest, especially since high-power experiments in the last few years seem to show it as a very promising approach to controlled fusion.

There's a good article about sfs z-pinch as a form of nuclear propulsion from plasma physics professor Dr. Uri Shumlak and a few of his colleagues at Researchgate that I will link here. Since this article was written there's been quite a bit of progress in terms of the performance metrics of sfs z-pinch experiments, which, although primarily in research to try to create an economical fusion power plant, are nevertheless directly in line with questions about the feasibility of such systems in a fusion rocket given their very similar core designs.

But even a fusion propulsion system like this version conceptualized by Robert Freeland that's heavily optimized for efficiency is going to top out at maybe 10-15% of c, and it would take a looooooong time to accelerate to that speed-this nearly kilometer long conceptual probe would take about a century to reach alpha centauri, and all it can do is blast through the system and beam back pictures to earth since it has no fuel left over to slow down. And this is just the propulsion problem! Interstellar travel is probably not absolutely impossible, but it's really REALLY hard.

 

[John J.]

- Did nuclear fission violate the law of conservation of energy?

No.
And fission not violating conservation of energy would have been known to a few in 1905.

 

[Kacmarek]

No.
And fission not violating conservation of energy would have been known to a few in 1905.

Wasn't nuclear fission and the strong and weak nuclear forces (binding protons and neutrons in the nucleus) discovered in the 1930s ?

Much of what we know about the universe has been discovered in the 20th and 21st centuries

If a force binding constituents of quarks inside protons is discovered tomorrow and it can be harnessed to deploy much large amounts of energy - it would be new physics which we do not know now

Why should we assume that physics and properties of matter/energy will hit a wall and new solutions wont be found

Newton didnt know about protons or neutrons or GR

Einstein didnt know about the black holes existing in space as physical manifestations of solutions to his equations though it had been predicted theoretically

 

[MyMatesBrainwashed]

Why should we assume that physics and properties of matter/energy will hit a wall and new solutions wont be found

I think you meant has, not will, cos the concept of there not being a wall AT ALL is pretty mind blowing.

 

[FatPhil]

Mmm, I sort of disagree.
The laws of thermodynamics, and the theories of relativity, are based on observed properties of the universe.
As far as we currently know, they apply everywhere.

I'd like to think that with sufficiently advanced technology humans will achieve extraordinary things, but there's no reason to believe that, say, we'll ever get more usable energy out of a system than exists in that system.

I don't remember who said it, but someone once came up with a pretty good rule of thumb with "if if violates the laws of thermodynamics, it's probably wrong". Whoever it was, he's been right every time so far.

Source: https://www.youtube.com/watch?v=5PYDVftZBo4


This related one, however, I can attribute:
"Science is at no moment quite right, but it is seldom quite wrong, and has, as a rule, a better chance of being right than the theories of the unscientific" - Bertrand Russell (1959)

 

[Eburacum]

I don't know....the internet and the various means of accessing it? As a teenage "someone" in 1970, I would have found it "astounding" to know there would be technology in my life time that allowed me to do what I'm doing right now.

Ha! I was already writing science fiction in 1970 (at the age of 14) and one of the things I imagined was an Internet-like electronic media channel. However my foresight was limited by lack of imagination, and I thought it would be just a way to access news from round the world. Never imagined that everyone would be texting constantly, even when cycling in traffic.