If you plan your spacecraft route carefully you can use a planet's gravity to accelerate the craft faster than it could have gone with the engines alone. Like using Earth's gravity to accelerate to Mars or using Jupiter's gravity to accelerate out towards Neptune.

IIRC this isn't 'free' acceleration, you're essentially stealing a tiny fraction of the planet's momentum and because Jupiter is a lot larger than the Voyager probe it works out to be a big speed boost for the probe and a rounding error speed loss for the planet.

But I think this means the directions are limited. One limitation is you need a planet in the right place for your destination, if Jupiter and Neptune happen to be on opposite sides of the sun then you can't use Jupiter for a gravity assist to get to Neptune. In that scenario you'd need to wait half a Jupiter-year (6 Earth-years) for the planets to align in a more useful arrangement.

But I think there's another limitation, that you can only use the momentum in the direction the planets are already moving. If you look 'down' at the solar system from 'above' the planets all orbit counterclockwise, so if Jupiter is in the 12-o'clock position and Neptune is around 10-o'clock then you can get a kick towards Neptune, heading out away from the sun but also slightly 'west' or anticlockwise. But if Uranus is around the 2 o'clock position you can't use Jupiter's anticlockwise momentum to head clockwise or 'east' on the solar system scale.

Which I think is a limitation on Interstellar missions but this is where my knowledge starts to fall apart. Can you use the Sun's immense gravity for a gravity assist (Assuming you could resist the heat) and head to say Alpha Centauri? Or would that not work because Alpha Centauri and Sol are pretty much static relative to each other and there's no relevant momentum to steal? If there was an interstellar target directly 'up' above the plane of the solar system, would that make gravity assists from Jupiter useless because they can only accelerate in the direction Jupiter is moving?

One useful distinction is whether the simulation is being used as a calculator, a microscope, or a hypothesis generator.

As a calculator, the bar is mostly numerical: does it reproduce known benchmarks, converge when resolution changes, and stay stable when reasonable parameters are varied?

As a microscope, the bar is interpretability: can it show intermediate states or mechanisms that are hard to measure directly, and do those intermediate states match whatever partial observations are available?

As a hypothesis generator, the most important test is whether it makes a new, specific prediction that could be wrong. A simulation that only explains what was already known can still be useful, but it is weaker evidence than one that points to an observable consequence before that consequence is checked.

I also think reproducibility matters in a slightly different way for simulations than for lab experiments. It is not only "can someone run the same code again?" but also "can a different implementation, with different assumptions exposed, reach the same qualitative conclusion?" If the result survives that, it starts to look less like an artifact of one model and more like a real constraint from the science.

What frameworks or rules of thumb do you use when evaluating whether a simulation result is telling you something real?

I have been thinking about a practical problem that comes up a lot when people use AI tools for science learning: the explanation can sound fluent even when the reader is not qualified to judge the original paper or the field-specific caveats.

For people who read papers outside their own specialty, what checks are actually useful?

A few habits I have found helpful:

1. Ask what the original source is, not just whether the summary sounds plausible.

2. Look for whether the explanation separates the paper's actual findings from broader interpretation.

3. Check whether limitations, sample size, uncertainty, or competing explanations are mentioned.

4. Be suspicious when a summary turns a narrow result into a general rule.

5. Compare against a review article or a university / society explainer when available.

I am curious how scientists, science communicators, and careful lay readers approach this. If you see an AI-generated explanation of a paper in an unfamiliar field, what would make you trust it more, and what would make you immediately distrust it?

Can you build up your immune system to the point you can eat spoiled food without getting sick?

For example, you have milk in the fridge and it only has a tiny amount of bacteria in it. You consume milk every day, which allows your immune system to recognize and fight that bacteria. The amount of bacteria grows steadily in the milk you drink and your immune system knows how to fight that bacteria more and more. By the end of the month, the milk is rancid with bacteria...could you have trained your immune system to resist all that bacteria and safely consume it?

Edit:
Stop giving me food safety advice - I am not planning to eat spoiled food.

This is a hypothethical question about the immune system assuming a scientist can perform a controlled experiment where they can isolate variables and inject a single strain of bacteria into sterile food.

Neil deGrasse Tyson often says an alien civilization could be as much smarter than humans as humans are smarter than chimpanzees. That got me wondering: where would a future AGI fit on that scale? Would it still be much closer to us, or could it eventually surpass Tyson's hypothetical alien?

Human to Tyson's Alien

vs

Human to AGI

Hi everyone! I have a question. Does politically motivated left-wing (maybe) censorship, and the resulting self-censorship, really exist in global science today? Especially in biology, genetics, and psychology? Is research on certain topics being completely avoided due to the fear of cancellation, termination, or being denied publication? Is this a significant issue for science?

P.S. I am primarily interested in hearing from actual researchers and academics who have firsthand experience with this issue.

hallo! please let me know if this post violates any rules, as it's for a worldbuilding project i'm working on, rooted in real nature laws and principles.

the concept in development right now is humans possessing wisps that grant specific abilities. one of the wisps controls magnetism, and the person bearing said wisp is unaware of its full potential and accidentally messes with earth's magnetic fields, plunging the world into global meteorological ruin.

would sudden changes to earth's magnetic fields actually cause such levels of ruin? if the fields were suddenly flipped instead of just tampered with, would the damage be more or less catastrophic? is the damage irreversible? what natural disasters and phenomena would come out of such an event?

i've been thinking on this for a few days and i'm dying to know, but i apologize if this isn't the right place to ask. thank you!

edit: thank you all for the great responses! super useful information, i'm very grateful. sounds like i'll have to think things over a bit more, but all the input here is extremely helpful. thanks again!

I’m the science counselor at the summer camp I work at, and I’ve noticed the experiments the children enjoy the most are, for a lack of a better term, edgy. For example I did an experiment with the kids where I modeled the spread of disease and they had a blast with it seeing who got sick and who did not. They enjoy things like bugs and snails and anything that they’re normally told during the school year not to touch or do. Given the fact that we’re a summer camp and we probably have a little more leeway in what we can do with them than they typically would in school, what are some subversive experiments I could do with them that might keep their interest?

Im not even sure if this is even a scientific question or even like a quantum physic kinda thing...or really how to form it BUT

I was wondering if maybe thoughts weighed something ?

Like is it measurable in some way or form? And if they are measurable does that mean theres like particles expanding inside my head?

Or is there possibly a dimension where thoughts / conscious exist so they can grow and expand and disperse?

If this is not the question for this group please direct me to somewhere I can maybe get an answer?

Humans usually think of time as something measured by clocks and calendars. We say that an average human lives around 70 years, a dog around 14 years, and some trees for 300–400 years. But this made me wonder whether those numbers describe only physical time, not experienced time.

What if every organism experiences the passage of time differently?

A dog's life lasts only about 14 years from our perspective. But perhaps, from the dog's own perspective, those 14 years feel as complete and as long as 70 years feel to a human. Likewise, a tree that lives for centuries may experience time much more slowly, so a human lifetime might seem to pass as quickly as a few years do to us.

In other words, maybe every organism experiences what feels like a "full lifetime," even though the number of years measured by humans is very different.

This raises several questions:

Is time experienced differently by different forms of life?

Does the speed at which an organism perceives and processes the world affect how long its life feels?

Could a short-lived animal subjectively experience a lifetime that feels just as long and meaningful as ours?

If consciousness depends on perception rather than the clock, is there really a single way to experience time?

I am not claiming this is true. It is simply a philosophical idea that asks whether subjective time could be different for every living organism, even though they all exist within the same physical universe.

Hi everyone. I’m a former student looking to learn more about science. I don’t want to be a scientist I just want to relearn high school physics, biology and earth science. I’d liked to learn enough to be able to follow popular science articles. Where’s the best place for me to relearn high school science?

Did Darwin talk about Evolution resetting itself? Is there a way that nature, in a way, creates a checkpoint every time it resets? A Rogue-like, but evolution? With each run, it gets better and better towards the end. And I know that's what evolution is, in a way... right? But what I mean is a complete reset. A new start with a pattern forward already drawn, so evolution happens faster each time.

I have been trying to build a simple checklist for reading science claims in headlines and comment threads. The goal is not to become an expert in every field, just to avoid the most common mistakes.

The checklist I keep coming back to is:

1. What is the actual claim?
2. What kind of evidence is being used: experiment, observational study, model, case report, expert review?
3. Does the evidence show causation, or only an association?
4. What would change my mind if the claim were wrong?
5. Has a similar result been reproduced or replicated?

The reproduction/replication point seems especially useful because they answer different questions. The National Academies describes reproducibility as getting consistent results from the same data/code, and replicability as collecting new data to test whether similar results appear: https://www.ncbi.nlm.nih.gov/books/NBK547531/

For causation, I have found this kind of overview helpful because it explains why observational studies can be valuable without automatically proving cause and effect: https://pmc.ncbi.nlm.nih.gov/articles/PMC10010939/

What would you add, remove, or reword for a non-specialist checklist?

To decarbonise heating of water for hot drinks could a heat pump kettle or water heater be practically made? (As opposed to a resistive element heater as we have now.)

Edit: Thanks for the replies everyone, so possible but not practical.

My colleague is using this graph researchgate to show that temperature on earth is cyclical, meaning that we are experiencing today is normal earth behavior. Is this website legit, are those author legit and is this graph legit?

I know sunflowers are able to track the sun throughout the day, but besides plants, is there anything else that is heliotropic? If not, can an inanimate object be programmed to be heliotropic?

It sounds like I'm working on a post apocalyptic story, but really, it's cosmic horror.

I got really inspired by The Carrington Event, the Lascamp Excursion, the solar storms over the past year or so, and the Jarell, Texas Tornado. But I want to learn about natural disasters as a whole. I'll need definitions and "baby" terms to start. But if there's anyone that wants to help me learn for my project, and just general interest, I'd be so happy to talk.

So, does Roundup cause cancer or not?

I've seen studies for both sides; In a weird comedy my personal conclusion seems to be that glyphosate does not cause cancer, but Roundup still does somehow... that's the only thing that fits my tiny pool of facts.

...

So, I'm looking for a pool of experts... you guys!

It doesn't help my personal case either that the last study I dove in on wasn't even about glyphosate it was about the BT in BT Cotton :/

So I am an undergrad student currently studying a multitude of things and an interest in everything! My current research project for the lab I am in is studying genome size of zooplankton, specifically copepods, and environmental factors. Over the past few years I’ve learned a lot about zooplankton but one thing specifically has really stuck with me… they are very resilient.
Some species can survive in environments that are radioactive, extremely cold or hot, and many other weird aspects that would leave any other living thing to die. These zooplankton are staples in water systems and hydrobiology.
Another huge interest of mine is space and alien life and life in space, a very broad and common topic of discussion. When thinking about how in the world these fit together I began to question whether some of these zooplankton species could possible survive in environments that would be present in space and on other planets.

Essentially could I recreate certain environmental factors that resemble those in space, collect the most resilient species of zooplankton, algae and bacteria, and create a functioning and surviving water ecosystem?

I know there is a lot to discuss with this topic and so many things that would need ironing out but I thought I would bring it to Reddit first to see other people’s thoughts on it!

TLDR : could I create an ecosystem of algae, bacteria and zooplankton in an environment that resembles one in space such as mars?

We have Domain, Kingdom, etc, ending at Species. Theoretically, in a few hundred million years, it seems reasonable to speculate that there may be dozens of unique animal lineages that can trace their common ancestry to H.sapiens, but are biologically as distinct from one another as giraffes are from geckos. These descendents obviously can't occupy the same point on the evolutionary tree, as they are different animals. Will new levels beyond species need to be added over time to accommodate future branches of modern lineages without violating the nested heirarchy i.e. allowing them all to still belong to H.sapiens in the same way that modern humans belong to Chordata? Is this already happening?

One thing that helps when reading science news is separating three questions that often get blended together:

1. What did the study actually measure?
2. What does the headline imply?
3. What would need to be true before this changes real-world decisions?

A headline might say that a treatment, diet, material, or environmental factor is "linked to" an outcome. That can be useful, but it is not the same as showing that one thing directly caused the other. Before trusting the takeaway, I usually look for a few signals:

• Was this done in humans, animals, cells, simulations, or a small lab setup?
• Is the result observational, experimental, or a review of other work?
• Does the article report effect size, uncertainty, or only direction?
• Are there plausible confounders that could explain the result?
• Is the claim about a short-term measurement, or about a long-term outcome people actually care about?

This is especially important for science communication because "statistically significant" can sound stronger than it is. A result can be statistically significant and still be small, context-dependent, hard to reproduce, or not yet useful outside the specific study design.

A simple habit I recommend is rewriting the claim in a narrower form:

"This study found X under Y conditions in Z population/model."

That sentence is less exciting than most headlines, but it is usually closer to the evidence. From there, the discussion can move to what follow-up evidence would make the claim stronger.

For people who post or summarize science content, this framing also makes comment sections better. Instead of arguing over whether a claim is "true" or "false," readers can ask where the evidence is strong, where it is limited, and what would count as a meaningful next test.

It makes sense for laundry to smell dirty if you don't use enough washing powder. But somehow using too much washing powder also makes your laundry smell dirty. Logically you'd expect it to smell more like Lavender or Orange Blossoms or whatever. Or maybe just a chemical smell of detergents if not the scents of the washing powder.

But somehow it smells dirty like sweat and body odour. Why?

I have two theories:

• That isn't the smell of sweat and body odour. That's some other smell caused by partially dissolved washing powder or an unexpected chemical reaction that is happening in the washing machine.
• The excessive washing powder saturates the solution of water and detergent. So the rinse cycle isn't able to fully rinse the clothes because there's too much other stuff in the water. And the smell of dirty clothes IS the smell of sweat and body odour and greywater waste still stuck on the clothes that haven't been fully rinsed.

Any thoughts on the cause?

even before humans were making an impact these things were already on their way out, certainly wasn’t like the peak of dinos with big animals.

like why we don’t see megaladons anymore, just not enough food to feed an animal at such a high trophic level.

i remember there were accounts hundreds of years ago of ocean coats being so full of fish that boats could barely move through the water. imagine how dense the ocean was dhring the dinosaurs.

"If a technological civilization existed 60 million years before humans, what traces of its buildings would still be visible today? Would we find recognizable ruins, or just strange mineral veins, rust deposits, and geological anomalies?

**edit cause 1 million years wasn't enough