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Neutrinos and gravitational waves are indeed known for their ability to traverse the Earth with minimal interaction, making them extremely difficult to detect without specialized equipment.
The Ghostly Neutrinos
Neutrinos are subatomic particles produced in nuclear reactions, like those in the Sun or supernovae. Dubbed "ghost particles," they interact so weakly with matter that they can pass straight through the Earth—about 100 trillion per second through your body alone. Detection requires enormous facilities like IceCube in Antarctica, which catches rare interactions in ice.
Gravitational Waves: Ripples in Spacetime
Not particles per se, but waves from massive cosmic events like black hole mergers. They stretch and squeeze space itself, passing through Earth unimpeded. First detected in 2015 by LIGO, they offer a new way to "see" the universe without light.
Here are some other particles or phenomena that can similarly pass through the planet largely undetected, based on current physics understanding. Note that some of these are hypothetical or speculative, as direct detection remains elusive.
Particles from Dark Matter Candidates
Dark matter is estimated to make up about 85% of the universe's matter, but it interacts so weakly with ordinary matter and light that particles associated with it can stream through the Earth (and everything else) without noticeable effects. Trillions could pass through your body every second.
- Weakly Interacting Massive Particles (WIMPs): These are leading candidates for dark matter. They would pass straight through ordinary matter due to their weak interactions, similar to neutrinos but potentially more massive.
- Axions: Ultralight particles proposed as another dark matter candidate. They interact even more feebly than neutrinos, allowing them to travel through the Earth unimpeded.
Hypothetical Quantum Gravity Particles
- Gravitons: If gravity is mediated by particles (as predicted by quantum gravity theories), gravitons would be massless and interact only gravitationally, enabling them to pass through the Earth without detection. However, they remain undetected and purely theoretical.
Other Exotic or High-Energy Particles
- High-Energy Muons: These are charged particles from cosmic rays that can penetrate deep into the Earth (many kilometers) if sufficiently energetic, but they don't typically pass all the way through the planet without interacting. Detection is possible but requires underground facilities.
- Sterile Neutrinos: A hypothetical type of neutrino that doesn't participate in the weak nuclear force, making them even harder to detect than standard neutrinos while still passing through matter effortlessly.
These examples highlight the challenges in particle physics, where weak interactions allow penetration but complicate observation. Ongoing experiments like those at CERN, IceCube, or dark matter detectors (e.g., LUX-ZEPLIN) aim to catch rare interactions from such entities.
The Cosmic Microwave Background (CMB) is the remnant radiation from the Big Bang, consisting of microwave photons that permeate the universe in all directions. It's often detected on Earth using ground-based or space telescopes, but unlike neutrinos or gravitational waves—which can traverse the entire planet due to their extremely weak interactions with matter—CMB radiation does not pass through the Earth without detection or absorption.
Here's why:
- Interaction with Matter: CMB is electromagnetic radiation in the microwave spectrum (wavelengths around 1 mm to 1 m). Microwaves are readily absorbed or scattered by dense materials like rock, soil, and water in the Earth's crust and mantle. The planet is essentially opaque to these wavelengths, so CMB photons impinging on one side of the Earth cannot emerge from the opposite side undetected.
- Detection on Earth: We observe CMB from the sky because some of it penetrates the atmosphere (which is relatively transparent to microwaves in certain bands), allowing ground-based detections like the original 1965 discovery in New Jersey. However, this is surface-level observation of incoming radiation from space, not transmission through the planet itself.
- Comparison to Other Phenomena: Neutrinos barely interact via the weak force, letting trillions pass through the Earth per second. Gravitational waves ripple spacetime and aren't blocked by matter. CMB, being photonic, follows the rules of electromagnetic opacity in solid bodies.
If CMB were to "pass through" the Earth, we'd need underground detectors picking it up from below, but that's not possible due to absorption.
For ground-based observations of the Cosmic Microwave Background (CMB), there is indeed a difference between sunny (clear) and cloudy days in terms of measurement quality and interference. The CMB signal itself remains constant and isotropic regardless of Earth's weather, but the atmosphere acts as a filter that can degrade the data collected by telescopes on the surface.
Key Effects of Weather on CMB Detection
- Atmospheric Interference in General: The Earth's atmosphere, particularly water vapor, absorbs and emits radiation in the microwave frequencies where CMB is observed (typically 30–300 GHz). This creates noise and contamination that must be filtered out during data analysis. Ground-based CMB experiments are designed with this in mind, often using techniques like rapid scanning or multi-frequency observations to subtract atmospheric signals.
- Cloudy Days: Clouds introduce additional liquid water and ice particles, which enhance microwave absorption and emission. This increases opacity (making the atmosphere less transparent) and adds thermal noise, potentially reducing the signal-to-noise ratio for CMB measurements. In severe cases, like heavy cloud cover or rain, observations might be paused or heavily compromised because the extra water content scatters and attenuates the incoming CMB photons more than on clear days.
- Sunny (Clear) Days: With fewer or no clouds, there's less water-related interference, leading to clearer skies and better data quality. However, even on sunny days, residual water vapor (humidity) can still play a role, which is why many CMB telescopes are located in high-altitude, dry sites like the Atacama Desert in Chile or the South Pole to minimize overall atmospheric effects.
Comparison to Day vs. Night
There's generally little to no significant difference in CMB detection between day and night for the same reason the CMB is constant—the primary interference comes from atmospheric composition (like water vapor levels), which typically doesn't fluctuate dramatically over a 24-hour cycle unless weather changes. Daytime might introduce minor additional noise from solar radio emissions or ground heating, but modern instruments account for this with calibration. Night observations are sometimes preferred for optical astronomy due to darkness, but for microwaves, it's less critical.
Mitigations and Space-Based Alternatives
To avoid weather-related issues entirely, space-based missions like the Planck satellite or COBE observe CMB from orbit, where there's no atmospheric interference at all. Experiments like those on satellites map CMB from orbit to avoid atmospheric interference, but again, that's not about planetary penetration. Ground-based setups, while affected, provide complementary data with larger telescopes and can achieve high precision by selecting optimal weather windows and using advanced filtering.
References
- Dark matter - Wikipedia - https://en.wikipedia.org/wiki/Dark_matter
- What gravitational waves can say about dark matter - https://www.symmetrymagazine.org/article/what-gravitational-waves-can-say-about-dark-matter?language_content_entity=und
- Scientists Used Neutrinos to Map the Milky Way. It Could Help Them ... - https://spaceref.com/science-and-exploration/scientists-used-neutrinos-to-map-the-milky-way-it-could-help-them-find-dark-matter-and-gravitational-waves/
- I'm struggling with the logic behind dark matter and dark energy - https://www.reddit.com/r/astrophysics/comments/1jhx5eb/im_struggling_with_the_logic_behind_dark_matter/
- Scientists accelerate the hunt for dark matter with gravitational waves - https://www.innovationnewsnetwork.com/scientists-accelerate-hunt-for-dark-matter-with-gravitational-waves/34553/
- First 'ghost particle' image of Milky Way galaxy captured by scientists - https://www.nsf.gov/science-matters/first-ghost-particle-image-milky-way-galaxy
- Dark Matter - Institute for Gravitation and the Cosmos - https://igc.psu.edu/topics/dark_matter/
- Neutrinos have mass, reshaping our understanding of the cosmos - https://www.facebook.com/groups/775801081313358/posts/1067874385439358/
- Probing dark matter inside Earth using atmospheric neutrino ... - https://link.aps.org/doi/10.1103/PhysRevD.107.115030
- Identifying dark matter - CERN Courier - https://cerncourier.com/a/identifying-dark-matter/
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