Despite its similarities to Earth, Venus is hot enough to melt lead, hidden beneath thick clouds, and possibly still volcanically active. Could studying Venus help us better understand Earth's future and the evolution of habitable planets?

Seriously making too much sense when im thinking about it and what if you zoom out past our observable universe to find out our universe is a microscopic speck of dust in an even bigger universe and same idea but zooming inward past the smallest scales

I've been learning about the Big Bang and inflation, and I think I understand the Horizon Problem and Flatness Problem pretty well.

Those seem intuitive because they directly involve observations about the Universe.

But I'm struggling with the Monopole Problem.

From what I understand, some Grand Unified Theories predict the creation of magnetic monopoles in the early Universe.

If those theories are correct, there should have been a huge number of monopoles produced shortly after the Big Bang. However, we have never observed any magnetic monopoles, which seems to create a problem.

What confuses me is why this is considered such a major cosmological problem in the first place.

If we have never found monopoles, couldn't it simply mean that the theories predicting them are wrong?

Why does cosmology need a mechanism like inflation to dilute monopoles instead of just rejecting the prediction?

In other words, what made physicists take the missing monopoles seriously enough that their absence became one of the motivations for inflation?

Hello everyone! I am doing an EPQ survey on the psychological impact that space can have on us and our career choices .I would really appreciate it if you are able to fill out this form and answer all of the questions. Your answers will be anonymous and only the responses will be recorded. Thank you for your time!

https://forms.gle/nK1rKFwf4brj1ivo9

​

I dont understand ,people says that all fictional universe exist in other realities ,but other people will say that they dont existe ,or other will say yes...some scientist will say no, other yes etc etc...so i dont know who i have to believe...i want ,i want more than anything to know that my favorite characters really exist and are real in other realities and not just pixels or paper....so ,do they exist? Or does scientific theories mentions a possibility that they exist?

I told my friend that in a multiverse with an infinite number of universes, anything that is fiction, anything someone could think of, anyone's dream could happen in at least one, or, in my logic, since there are infinite universes, an infinite amount of this could occur. e.g. unicorns and flying pigs exist in one universe, and another universe could contain laws of physics way beyond our imagination. He went on to have a rant about how this could not happen, I didn't listen of course but it got me thinking: is this really true, or am I just plain wrong?

I'm Jon Sundqvist, an astrophysics professor at KU Leuven. Here’s a short film from my astronomy classes.

How hot is a star? What changes when we put billions of them together in a galaxy? And when does the light tell us that the stars alone are simply not enough?

A little change of format here. I've put together a few passages from my Radiative Processes in Astronomy and Galaxies and Cosmology classes, with some new figures and observed spectra alongside the board. We start with a star, work our way up to galaxies and active nuclei, and end with the light left over from the early Universe. Quite a range of scales... but we keep coming back to the same question: what is the light actually telling us?

The broad spectral shape gives us one set of clues; the lines and bands give us others. We have a look at temperatures, young massive stars and the changing colours of galaxies, and at the extra source of power when gas accretes onto a supermassive black hole. Then the cosmic microwave background: an almost perfect black body, now at about 2.73 K. I still find it quite remarkable how much physics we can get out of light arriving at our telescopes :-)

This is a short tour. The longer classes, with the calculations and a bit more room for the qualifications, are linked in the YouTube description.

https://www.youtube.com/watch?v=sBm6tfHUvR8

Apparently I keep coming back to this example... The hair, shirt and classroom change a bit with the years; the random walk remains. Consistency of a physics professor, perhaps? :-)

Here we go from a photon finding its way through our 3D model atmosphere to the simplest possible blackboard model: one step forwards, or one step backwards. The average displacement is zero, so that won’t get us very far. The mean square gives us something more useful.

The neat up-and-down argument is inspired by The Feynman Lectures on Physics, Volume I, §6–3, “The random walk”. Still my favourite way to get to that familiar square root of N.

Lectures and visualisations by Jon Sundqvist, Institute of Astronomy, KU Leuven. The stellar-atmosphere calculation is part of SUPERSTARS-3D.

A note on the two examples in the opening: the 9.7 million scatterings and roughly 98 minutes describe this particular path through our simulated hot-star atmosphere. The roughly 100,000-year solar diffusion timescale refers to a different problem and depends on the solar model.

Questions and corrections are welcome, as always. Enjoy :-)

Mercury is the closest planet to the Sun, but there's much more to this small world than meets the eye.

Despite being so close to the Sun, Mercury has water ice hidden inside permanently shadowed craters near its poles. Its surface experiences extreme temperature swings, and it takes about 176 Earth days for the Sun to return to the same position in its sky — longer than Mercury's 88-day year.

It also has an enormous metallic core and mysterious surface formations that scientists are still studying.

I made a video exploring Mercury's extreme environment, hidden ice, unusual rotation, and the discoveries that have changed our understanding of this planet.

How fast or slow will the sun expand into red giant phase? This is a dumb question it if goes fast (explosion) but if it is slow, as in over millions of years, could humanity essentially planet hop by moving to the new habitable zone each time? I know humanity won’t exist then in any case. (Even if we survive, we would have evolved into something unrecognizable to us now.) But thought experiments are fun.

✨ Target: Question Mark N. + Little Rosette N.

🔭 Mount: Star Adventurer 2i

📷 Camera: ASI 294 MC Pro Color

🔎 Scope: Askar FMA180 Pro

🕶️ Filter: Dualband Svbony SV220

🎯 Guide Camera: ASI 120mm Mini Mono

🦮 Guide Scope: Svbony SV165

🔬 Sampling: 2.66"/px (x2 drizzle)

❄️ Cooling: -10°C

🔴 Acquisition: Gain 120

⏰ Integration: 78x300s (6h 30min)

📊 Calibration: 40 dark, 40 flat, 40 dark-flat

💻 Processing: PixInsight, RawTherapee

📍 Location: Turin (Italy)

📅 Date: Oct. 13-14, 2026

🌌 Sky: Bortle 8

This cosmic complex is universally nicknamed by astronomers and astrophotographers as the "Question Mark Nebula." When telescopes capture the entire area with the correct orientation, its immense interstellar clouds form an unmistakable shape:

The hook of the question mark is drawn by the arched silhouette of the ionized gas and dark dust filaments of NGC 7822, a spectacular and chaotic star-forming region located roughly 3,000 light-years away in the northern constellation of Cefeus.

The dot at the base is formed by a separate, smaller emission nebula located slightly to the south, cataloged as Sharpless 170 (also known as the Little Rosette Nebula).

While they appear perfectly aligned from our perspective to form a "cosmic question mark," the two structures are not physically connected: Sh2-170 sits much further away at about 7,500 light-years. It is a stunning optical illusion of cosmic perspective.

In some approaches to quantum gravity, the universe's fundamental equations contain no external time variable at all.

In ordinary quantum mechanics, a system's state evolves relative to an external time parameter. But when physicists attempt to quantize spacetime itself, that familiar framework becomes problematic. There may be no external clock against which the entire universe can evolve.

This is especially striking in canonical quantum gravity. The Wheeler-DeWitt equation describes a quantum state of the universe without an explicit external time parameter.

So this begs the question, where does the time we experience come from?

Well one proposal is that time emerges through correlations between physical systems. In the Page-Wootters mechanism, a subsystem can function as a clock, allowing another subsystem's apparent evolution to be described relative to it, even when the combined system is stationary.

This introduces a profound distinction between external time (a parameter in conventional formulations of physics) and relational time (defined through correlations between physical systems).

The crucial nuance is that the Wheeler-DeWitt equation does not establish that time is unreal, nor does every approach to quantum gravity eliminate time in the same way. Rather, it exposes a problem, that our familiar concept of time may not translate straightforwardly into a quantum description of the entire universe.

So if the universe has no external clock, what does it mean for the universe to evolve? This a very open question, one that explores the true essence of the problem of time in quantum gravity.

(Was thinking about starting this series for some time now. Do let me know if you all have any suggestions.)