The Physics That Makes Interstellar Travel IMPOSSIBLE ...

[UncleDave]

If we can find a way to turn electrical power at high efficiency into approx 1G of forward thrust then we can figure out how to travel to nearby stars.

We've got power plants with enough duration and time on ship travel is workable at 99%+ the speed of light . Time back on earth is a long time though.
It buys us a few light years in exploratory diameter.

What's the lifespan of a carrier sized shipboard nuke 20 years or a submarine 15?

Not quite the stuff of Sci fi dreams but it opens up a whole solar system of exploration and makes some deeper range stuff viable.

 

[PWMDMD]

Yet another mystery of the cosmos..... If a nutron star spins at something like 700 revolutions per second, how does it not tear itself apart from centrafugal force?

Not a mystery. Just maths...

700Hz Neutron star with a radius of 10-12km would have a mass of ~ 2.8 x 10^30 kg (2.8 with 30 zeros after it) and a period of about 1.4ms. We are comparing centrifugal force to gravitational force.

Angular velocity = w = 2(Pi)F where F is 700Hz = 4400rads/s

Centrifugal acceleration = a = w^2R where R is the radius so a = (4400)^2 x 10^4 = 1.9 × 10^11

Gravitational acceleration = g = GM/R^2 = where M is mass = (6.67x10^-11)(2.8×10^30)/(10^4)^2
g = 1.9 x 10^12 m/s^2

Gravity is roughly 10x greater than the centrifugal force. ( 1.9×10^12 vs 1.9x10^11)

Not a mystery at all...

Representative Example: A 700 Hz Neutron Star​

 

[MolaKule]

But their density is unimaginable. A teaspoon of a nutron star can weigh over 100 million tons. And then you have to factor in they spin at their equator at close to 25 percent of the speed of light.

That kind of centrifugal force is hard to comprehend.

I think you're referring to the total or overall density.

According to the hypothetical model in this diagram the densities and pressures are higher as you go down toward the core as would be expected. I would assume the inner core of neutron gasses would be spinning faster than the outer layer of ions and electrons, so there is most likely some sheer between the layers.

https://commons.wikimedia.org/wiki/...taways#/media/File:Neutron_star_structure.JPG

 

[MolaKule]

I would assume the inner core of neutron gasses would be spinning faster than the outer layer of ions and electrons, so there is most likely some sheer between the layers.

https://commons.wikimedia.org/wiki/...taways#/media/File:Neutron_star_structure.JPG

A potential PhD thesis: "Neutron-Layer Shear and its ElectroHydroDynamics Effects"

Anyone, anyone?

 

[Arc]

Person A: "What do you think about Shakespeare?"

Person B: "I don't think Shakespeare's stories are any good"

Person A: "Have you ever read Shakespeare?"

Person B: "No."

Humans are funny animals who not only love to opine about topics they have little to no knowledge about, they love to vehemently opine about these topics. It's hard to say what we do or don't know about the universe when you yourself don't know what we do or don't know about the universe.

It doesn't fall apart at all and the counter to your argument is of course unknown unknowns exist but that is a tautological argument and it doesn't address what we are talking about here. The existence of unknown unknowns does not invalidate known knowns. If hidden variables existed in Newton’s time, that did not make Newtonian mechanics false. It made it incomplete. And incompleteness is not ignorance.

Your position confuses incompleteness with ignorance. Scientific knowledge does not require omniscience. It requires: 1. Predictive accuracy, 2. Internal consistency, 3. Reproducibility, and 4. Falsifiability. By those standards, we know an extraordinary amount.
Modern physics allows us to: 1. Predict planetary motion centuries in advance using General Relativity; 2. Design GPS systems that require relativistic corrections to function; 3. Build semiconductors using quantum mechanics; 4. Detect gravitational waves exactly as predicted by Einstein; 5. Model stellar evolution and nucleosynthesis with high precision. If we “knew nothing,” these systems would not work.

The real power of what we know is that multiple independent frameworks converge on the same empirical truths: 1. Quantum Mechanics accurately describes subatomic phenomena; 2. General Relativity describes gravity at cosmic scales; 3. The Standard Model predicts particle interactions with extreme precision; 4. Cosmology predicts the Cosmic Microwave Background spectrum before it was measured. When independent models align with experimental data across scales, that is strong evidence of real knowledge. There are known open problems: 1. Quantum gravity; 2. Dark matter; 3. Dark energy; 4. Unification and surely there are unknown open questions too. But having unanswered questions does not erase experimentally validated knowledge. Medicine does not become useless because it cannot cure every disease. Physics does not become ignorance because it lacks a Theory of Everything.

Scientific knowledge is provisional, but that does not make it arbitrary. We do not need to know “everything” to know “a great deal.” Physics has produced a coherent, predictive, experimentally validated model of reality spanning 15 orders of magnitude in scale. That is not ignorance. That is extraordinary knowledge, even if incomplete.

However, if YOU don't have a general grasp on that knowledge then sure, I can see why you hold the position you do but that's your issue, not an issue with what humans know.

I always hear about science being fact so I just tell them I agree and that's why I'm sticking with a flat earth.

 

[Arc]

His arguments are quite sound actually, because the stuff we do know is 100% replicable and measurable with a very high degree of accuracy.

The fallacy of your argumentation is that, in your view the things we don’t know will somehow invalidate the things we do know, once we discover them.

The problem arises when someone says this is what we do know and present it as factual to the public when in actuality it is theory. The general public doesn't understand that science is ever changing.

 

[buster]

A lot of people write him off, but he may be on to something. Look up Navy Physicist/engineer Salvatore Pais.

 

[PWMDMD]

I always hear about science being fact so I just tell them I agree and that's why I'm sticking with a flat earth.

No one who does science or understands the process uses the term fact. It's simply the best ideas we have based on the data we have but it always provisional. The provisionality of it is what trips many people up because in their minds if it is not fact, then they somehow conclude it's just a guess. No, it is logical conclusions based on what is currently known and it works so well, you can have a super computer in your pocket that uses quantum mechanics to communicate with geosynchronous satellites that correct time for their velocity and the difference in the earth's gravitational field at their location and perfectly pin point your location. It is quite amazing what we know.

 

[KrisZ]

The problem arises when someone says this is what we do know and present it as factual to the public when in actuality it is theory. The general public doesn't understand that science is ever changing.

The exchange and this whole thread is about faster than light travel. And when it comes to this topic we have tons of facts, not theories.
We know that a photon has no mass, therefore anything with mass cannot achieve the speed of light. How do we know this? We have particle accelerators and we cannot accelerate protons, so nothing with any meaningful mass, to the speed of light, only 99.997% or thereabouts. What these experiments proved is that injecting more energy, increases the mass/energy of the particle, not its speed once it is close to the speed of light.

Therefore we have very solid, evidence based facts supporting the theory that nothing with mass can travel at the speed of light. Never mind going faster.

 

[Arc]

No one who does science or understands the process uses the term fact. It's simply the best ideas we have based on the data we have but it always provisional. The provisionality of it is what trips many people up because in their minds if it is not fact, then they somehow conclude it's just a guess. No, it is logical conclusions based on what is currently known and it works so well, you can have a super computer in your pocket that uses quantum mechanics to communicate with geosynchronous satellites that correct time for their velocity and the difference in the earth's gravitational field at their location and perfectly pin point your location. It is quite amazing what we know.

You know how the vast majority are now that they can just google something and start stating "facts". If it's on the internet it must be true. Sometimes I will take time to mess with them but usually I just move on.

 

[Arc]

The exchange and this whole thread is about faster than light travel. And when it comes to this topic we have tons of facts, not theories.
We know that a photon has no mass, therefore anything with mass cannot achieve the speed of light. How do we know this? We have particle accelerators and we cannot accelerate protons, so nothing with any meaningful mass, to the speed of light, only 99.997% or thereabouts. What these experiments proved is that injecting more energy, increases the mass/energy of the particle, not its speed once it is close to the speed of light.

Therefore we have very solid, evidence based facts supporting the theory that nothing with mass can travel at the speed of light. Never mind going faster.

What will you do years down the road and we find out that something can travel faster than light? At one time it was a "fact" that the earth was flat was it not? Maybe fact means something different to some people. For me it is never changing. What you said could indeed be true considering what we know but saying it is a fact is a stretch. I'm a retired Electrical Contractor and back when I was young and half way intelligent we discussed how electrons flow in a conductor. No matter how much theory we discussed it always came down to the fact that they travel only on the outside surface of the wire. People laughed at me and pointed to the facts constantly yet here we are today and now it's a fact that electrons flow through the conductor not just on the outer surface. Fact is an overused word. Just my opinion though, not a fact.

 

[KrisZ]

What will you do years down the road and we find out that something can travel faster than light? At one time it was a "fact" that the earth was flat was it not? Maybe fact means something different to some people. For me it is never changing. What you said could indeed be true considering what we know but saying it is a fact is a stretch. I'm a retired Electrical Contractor and back when I was young and half way intelligent we discussed how electrons flow in a conductor. No matter how much theory we discussed it always came down to the fact that they travel only on the outside surface of the wire. People laughed at me and pointed to the facts constantly yet here we are today and now it's a fact that electrons flow through the conductor not just on the outer surface. Fact is an overused word. Just my opinion though, not a fact.

If you get hung up on the word “fact” then I agree, there are very few “facts” that people can cite.

But replace the word “facts” with test, measurements, experiments and perhaps it’ll be easier to accept the reality of traveling at the speed of light as impossibility.

Yes, it used to be a theory based on math, but we have highly accurate and repeatable experiments now that prove the theory so far.

The fabric of space is theorized to travel faster than the speed of light, based on the redshift. And perhaps it is, but does it have mass? Nope, we don’t even know what that “fabric” is. So again, the theory seems to hold.

 

[Arc]

If you get hung up on the word “fact” then I agree, there are very few “facts” that people can cite.

But replace the word “facts” with test, measurements, experiments and perhaps it’ll be easier to accept the reality of traveling at the speed of light as impossibility.

Yes, it used to be a theory based on math, but we have highly accurate and repeatable experiments now that prove the theory so far.

The fabric of space is theorized to travel faster than the speed of light, based on the redshift. And perhaps it is, but does it have mass? Nope, we don’t even know what that “fabric” is. So again, the theory seems to hold.

I was just talking about those random people who show up in the forums saying "it's a fact" over and over and won't listen to anything else. They will copy and paste you to death with something they know nothing about to try and look intelligent. Myself I'm dumb as a rock compared to the really smart people so I don't try to be anything different. I'm just an old retired electrician that likes to ramble on because it's winter and it's cold outside.

 

[KrisZ]

I was just talking about those random people who show up in the forums saying "it's a fact" over and over and won't listen to anything else. They will copy and paste you to death with something they know nothing about to try and look intelligent. Myself I'm dumb as a rock compared to the really smart people so I don't try to be anything different. I'm just an old retired electrician that likes to ramble on because it's winter and it's cold outside.

These kinds of people are everywhere, including highly educated fields. Sprinkle in some arrogance and their “facts” are unbeatable, only in their mind of course.

 

[Astro14]

I was just talking about those random people who show up in the forums saying "it's a fact" over and over and won't listen to anything else. They will copy and paste you to death with something they know nothing about to try and look intelligent. Myself I'm dumb as a rock compared to the really smart people so I don't try to be anything different. I'm just an old retired electrician that likes to ramble on because it's winter and it's cold outside.

Gravitation is still a theory.

You are free to test it by walking off a tall building, perhaps.

Many of the things that you claimed were “facts”, like the flat Earth, as examples of what has changed, were simple belief. Not facts. And certainly not science.

Around 200 BC Eratosthenes not only knew the Earth was round, but he calculated the diameter to be within a few percent of what we know it to be today.

He was a scientist.

 

[Arc]

Gravitation is still a theory.

You are free to test it by walking off a tall building, perhaps.

Many of the things that you claimed were “facts”, like the flat Earth, as examples of what has changed, were simple belief. Not facts. And certainly not science.

Around 200 BC Eratosthenes not only knew the Earth was round, but he calculated the diameter to be within a few percent of what we know it to be today.

He was a scientist.

I wasn't around back then even though my grandkids think I'm that old but I would bet somebody said it was a fact.

 

[Astro14]

I wasn't around back then even though my grandkids think I'm that old but I would bet somebody said it was a fact.

There’s still people who claim the Earth is flat.

But the world is full of people who believe strange things, and claim that those things are facts.

That does not in any way reduce the validity of current scientific understanding.

Understanding evolves.

There is not always consensus.

Einstein himself rejected the notion of quantum mechanics, initially- but the very device on which you are typing your response requires that quantum mechanical principles be true for the semiconductors to work.

Einstein’s initial work on relativity was rejected by many. It was very controversial.

In fact, Einstein won the Nobel prize for the photoelectric effect, not for relativity, because of that controversy.

Decades later, Einstein was proved right. There are many great moments in astrophysics that proved relativity was true.

But proving Einstein was right did not make Sir Isaac Newton‘s work wrong or invalid. Newton‘s laws of motion are still absolutely accurate at the velocities humans normally experience.

The evolution of thought in science sometimes requires tearing down old ideas, and sometimes simply expands on the foundation.

 

[billt460]

There’s still people who claim the Earth is flat...........

And they take it all the way to full blown stupid. You're higher then he got when you put the gear down.

 

[barryh]

But proving Einstein was right did not make Sir Isaac Newton‘s work wrong or invalid. Newton‘s laws of motion are still absolutely accurate at the velocities humans normally experience.

Sir Isaac Newton himself said he "stood on the shoulders of giants" so he would understand that someone would eventually stand on his shoulders.

 

[bunnspecial]

A lot of people fall into the trap of thinking a scientific "theory" means "just a guess" since that's how it's incorrectly used in common language.

A theory is a piece of the scientific method, and actually a pretty "late" step in the scientific method.

For a refresher, as would be taught on day 1 of an intro level college science class, the scientific method looks like this

1. Observation-an event or phenomenon is observed that is contrary to current understanding, or has no explanation

2. Hypothesis-the scientist makes an educated guess as to an explanation for the phenomenon.

3. Experiment-a scientist designs an experiment to test the hypothesis

4. Analyze data which will either support or reject the hypothesis

This process can be repeated endlessly, and with sufficient data, two things can result

1. Scientific Law-describes a predictable result under specific circumstances. Laws are often mathematical relationships, and also often have defined limits.

2. Scientific Theory-essentially is a compilation of all hypotheses, proven and disproven, and experimental data to explain a big picture concept. A theory is often supported by one or more scientific law(i.e. the theory of gravity leans on Newton's laws of motion) but also often contains considerations for where the theory is not applicable. A theory may also be effectively an expansion of a previous theory.

In common usage, "theory" is often thought to be more like what the scientific method calls a "hypothesis." Even then, though, usage is often sloppy. A hypothesis can't just be a blind guess, and, more importantly, a valid hypothesis MUST be testable. A lot of what people call "theories" in colloquial use are blind guesses that can't be tested, so really they're not any part of the scientific method, they are just blind guesses.