What is Life: Definition and 1000 Discussions

Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased (they have died), or because they never had such functions and are classified as inanimate. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. Biology is the science that studies life.

There is currently no consensus regarding the definition of life. One popular definition is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve. Other definitions sometimes include non-cellular life forms such as viruses and viroids.
Abiogenesis is the natural process of life arising from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but a gradual process of increasing complexity. Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. The earliest known life forms are microfossils of bacteria. Life on Earth is probably descended from an RNA world, although RNA-based life may not have been the first life to have existed. The classic 1952 Miller–Urey experiment and similar research demonstrated that most amino acids, the chemical constituents of the proteins used in all living organisms, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. Complex organic molecules occur in the Solar System and in interstellar space, and these molecules may have provided starting material for the development of life on Earth.Since its primordial beginnings, life on Earth has changed its environment on a geologic time scale, but it has also adapted to survive in most ecosystems and conditions. Some microorganisms, called extremophiles, thrive in physically or geochemically extreme environments that are detrimental to most other life on Earth. The cell is considered the structural and functional unit of life. There are two kinds of cells, prokaryotic and eukaryotic, both of which consist of cytoplasm enclosed within a membrane and contain many biomolecules such as proteins and nucleic acids. Cells reproduce through a process of cell division, in which the parent cell divides into two or more daughter cells.
In the past, there have been many attempts to define what is meant by "life" through obsolete concepts such as odic force, hylomorphism, spontaneous generation and vitalism, that have now been disproved by biological discoveries. Aristotle is considered to be the first person to classify organisms. Later, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Eventually new groups and categories of life were discovered, such as cells and microorganisms, forcing dramatic revisions of the structure of relationships between living organisms. Though currently only known on Earth, life need not be restricted to it, and many scientists speculate in the existence of extraterrestrial life. Artificial life is a computer simulation or human-made reconstruction of any aspect of life, which is often used to examine systems related to natural life.
Death is the permanent termination of all biological processes which sustain an organism, and as such, is the end of its life. Extinction is the term describing the dying out of a group or taxon, usually a species. Fossils are the preserved remains or traces of organisms.

View More On Wikipedia.org
  1. DaveC426913

    Conway's Game of Life in Real Life

    Game of Life Playing out in rainwater on my door screen... Appears to be using highly permissive life/death parameters tho...
  2. R

    I Is low entropy found in something very hot?

    If we have a kg of something that is 100miljon Celsius degrees, and can controlably use this heat somehow, we can sustain life, grow crops, drive steam engines and with these we could build a whole city like New York, we can create a lot of mass with very low entropy, things that are very...
  3. Frabjous

    Detecting Martian Life: How Can We Find Evidence of Slow Life on the Red Planet?

    https://bigthink.com/hard-science/accidentally-killed-life-mars/ Interesting article about a type of life that might exist on Mars. It brings up questions on how do we test for the existence of life.
  4. O

    I Half life and radioactivity clarification

    As I understand, half life's are where unstable nuclear isotopes Undergo radioactive decay, where they emmit either aplha beta or gamma during this decay. I'm looking for some clarification on whether when an atom undergoes decay, does it then change into another element/ isotope of an...
  5. Kumail Haider

    Applications of gyroscope in daily life

    Hello! I was just started the topic gyroscopic motion These questions come to my mind. please guide me that how gyroscope is used in mobiles what is its function in mobiles and also want to know their role in aircrafts that how it helps pilot to determine the position of aircraft etc. Please...
  6. S

    Prolonging the Life of Poorly Accessible Rusted Steel

    I had a rear 3/16" OD steel brake line in my car fail due to rust. I spliced out the area with the hole with copper nickel line, but, I noticed that there's areas closer to the engine where the painted surfaces have bubbled a bit. Unfortunately, access is such that I can't splice fresh line...
  7. BillTre

    Origin of Life Chemistry interview with Bill Martin

    This video is an interview of Bill Martin (Martin wikipedia link) (one of the godfathers of modern origin of life chemistry) by Jitender Kumar about several origin of life issues. He has a lot chemical knowledge and expresses it clearly. Interesting to me, he places the formation of membranes...
  8. S

    Does Jimmy Carter's long life prove some exposure to radiation is OK?

    Former USA President Jimmy Carter seems to be near the end of his 98 years, and was one of the original US Navy nuclear engineers. Over 70 years ago, he led a team that extracted out the world's first melted down core out of a Canadian reactor, himself going 90 seconds into the "dead zone" -...
  9. N

    I What is the probability of life on exopanet LHS475b?

    Recently the James Webb Telescope discovered an exoplanet 99% the size of Earth. Its name is LHS 475 b. What is the probability that there is life on this planet?
  10. Nadia

    Calculations: Creep of Metals and the Life of a Rod

    I'm sorry I'm uploading lots of images because I don't know how to write equations here. PROBLEM DESCRIPTION I have to solve this problem: Figure P3.6: MY SOLUTION I did this: THE CORRECTION I got this as a correction: - Don't use the middle line in figure P3.6 in my calculations. -...
  11. Pipsqueakalchemist

    Engineering (material science) Fatigue life prediction using integral

    So for this question, I understand the math but just wanted to be clear on a few things. So I had this question on my midterm but instead of tensile and compressive stresses, it was tensile and tensile stress. I initially thought that the delta sigma in the integral was the maximum stress so in...
  12. S

    Can’t understand is "life" word banned in physics forum.

    Whenever I am posting anything related to "life" it got deleted! Does life not related to physics??
  13. S

    Exploring Life Perspectives: Survival, Doing Good, and Continuing the Human Race

    From my point of view: 1) survival 2) do something good to satisfy your inner soul and for others. 3) help to continue the race of human being 4) and die What others think about life?
  14. R

    Theories on how the food supply evolved along with life?

    Along with the endless complexities of life and the evolution of life, it occurs to me that at all points there had to be enough available nutrition for existent life forms - and that food supply itself had to go through a process of evolution. It seems self-evident that the environment of early...
  15. N

    B What would the planets look like in real life?

    I am of the total understanding that most astrophotography pictures are not a real representation of what objects actually look like... I guess I mean, it is not an accurate representation of what things would look like if you were actually the same distance closer as the picture's magnification...
  16. freelooooo

    How does Cmax decrease over time in human body? Use half life?

    I'm interested in chemistry but it's all new for me and I'm just starting out. I tried to do some calculations but got stuck... I was wondering, for example a supplement has the following values: Molar mass: 306.247 g mol-1 Tmax 2-4 hours Cmax 363.3 ng / ml Half life: 11.21 hours How do...
  17. C

    How might plant life look different on other theoretical planets?

    Got interested on how plants (and other things such as fungi) could evolve on other planets along with how plant life may flourish depending on the position of the planet to the sun, moon etc. I'm looking for any article talking about this or something similar.
  18. M

    Exploring the Paradox of Life in an Entropic Universe

    Not sure to ask here or in Physics/Cosmology. How could life have begun much less evolve (or even planets form) if according to the 2nd Law of Thermodynamics entropy always increases with time?
  19. ergospherical

    B Swimming at the Same Reynolds Number as Sperm: A Reflection on Purcell's Talk

    https://www2.gwu.edu/~phy21bio/Reading/Purcell_life_at_low_reynolds_number.pdf “It helps to imagine under what conditions a man would be swimming at, say, the same Reynolds number as his own sperm”
  20. Delta2

    What is the true meaning of life?

    What do you think is the meaning of life? My answer is two folded: The special meaning of life : After living almost 50 years on this planet and on the plane of the physical reality, I concluded that the meaning of life is to apply various laws in your life. The most important laws for me...
  21. BillTre

    Origin of Life Podcast with Nick Lane & Sean Carroll

    Here is a link to a recent (and good) Sean Carroll podcast with Nick Lane. I consider Nick Lane to have one of the most interesting views of Origin of Life issues. I consider his perspective to be biochemical and biochemical pathway heavy, which is very useful for these issues of...
  22. R

    Can reducing Boric acid concentrations extend the life of fuel assemblies?

    Hi, do you think that reducing Boric acid concentrations at the begin of the cycle would extend the like of the fuel assembly?
  23. T

    NASA Could Mars have supported life? NASA challenge wants your help

    Deadline April 18, 2022 Competition Eligibility at: https://www.drivendata.org/competitions/93/nasa-mars-spectrometry/rules/ HeroX Challenge page: https://www.herox.com/MarsSpectrometry Brief article: https://www.space.com/nasa-mars-habitable-herox-competition Good Luck, and have Fun! Tom
  24. A

    Essay on Life without Mobile phones today

    Could this be a good essay for school or college children to write a essay on "Life without Mobile phones today" as the essay title? The Mobile phones (Wireless technology) has impacted our lives and its hard for us where once upon a time we were using land line phones (wired technology) and...
  25. shivajikobardan

    Comp Sci 1 example of information system in real life?

    I am studying IS but I am yet to find an example of IS. Is database IS? Is expert system IS? What is example of IS? And this question came to me while studying about this issue-: is security policy same as security methods? justify your argument with appropriate example of Information system...
  26. dRic2

    Low battery life in sleep mode

    I have a 6 years old MacBook air, still running the OS of a couple of years ago. Lately, battery life is going down (around 4.5 hours of light/medium use) so I mainly use it as a desktop computer, connected to an external monitor. However, when I leave it in sleep mode (still on, but shell...
  27. shivajikobardan

    MHB My Failed University Life: Addictions, Depression, and Uncertain Future

    1) Really messed up my uni life. Indulged into various addictions like addiction of making money online. making free money. wasted almost 3 years of uni life in it. 2.5 years to be exact.. Didn't keep notes of any subject even though i passed subject with ease as I had good track record of being...
  28. W

    Is quantum entanglement life?

    hello: I don’t know where to post this and I think this is as good a place as any here. question: does quantum entanglement explain how we are? I am having trouble Even trying to express the question above. But, I just viewed PBS space-time series 6 episode eight: “how do quantum states...
  29. wrobel

    Is Smiling Allowed in Soviet Schools?

    Here are two pictures attached. The first picture is a photo from Russian secondary school 1967. The second picture is a painting by an American artist Norman Rockwell. He used the photo as a sample. There are ordinary children at the photo, the girl laughs. At the painting the children stare...
  30. shivajikobardan

    I wasted 3 years of my uni life on unproductive and useless things

    https://www.physicsforums.com/threads/regret-induced-jealousy-how-to-deal-with-this.1011135/#post-6586239 I made a post this few days ago but I believe this is different than that post. How do I get over this? I wasted time trying to make online income, creating blogs. I didn't realize full...
  31. K

    Frequently switching a lamp ON and OFF in short time reduced bulb life?

    I had a lamp that was good for 10 years but two years ago it was burnt out, I replaced it and in this two years we have a naughty kid playing with it, it is burnt out recently again. Is it likely due to his behavior (switch it ON and OFF within short time) or quality of light bulb in recent...
  32. Lren Zvsm

    Sapient Life Indigenous to a Planet Orbiting a Red Dwarf

    I am considering writing a story that features aliens indigenous to a planet orbiting a red dwarf star. Even so, because of its proximity to the red dwarf, the planet's surface receives much more radiation than Earth's surface does. What is more, the planet has no moon to stabilize its...
  33. paulrk

    Calculate complexity of the game of life (cellular automata)

    I want to calculate the kolmogorov complexity of n evolution of a game of game of life(game of life is a kind of cellular automata). I’m not searching for the complexity of a certain pattern of cells but for the total complexity of an initial set of cells over n evolutions. Does it make sense to...
  34. S

    What are the odds that other life exists?

    Summary:: Like how is it possible that Earth was just perfectly made for life? It seems impossibly unlikely that Earth would be able to harvest life. I also heard that the moon is exactly 400 times smaller than the sun and 400 times the distance from each other, which makes solar eclipses...
  35. C

    The importance of water for life

    Hi PF, I'm teaching a college level introductory course about planet Earth and we are briefly discussing the importance of water for life. This is not covered in our textbook but I thought it was important to cover. I found some good resources...
  36. J

    Can the Genesis Project really seed the galaxy with robots?

  37. Eclair_de_XII

    What's the point of life? Struggling to find purpose and joy in daily existence.

    Nothing I do seems to matter anymore and it is becoming nearly impossible for me to take interest in the world around me.
  38. S

    Question Regarding the Shelf Life of Mineral Supplements

    I'm seeing somewhat conflicting advice for storing supplements long term (longer than 5 years). First, supplements are supposed to lose their potency with age, but, minerals are supposed to be stable for a very long time- possibly even indefinitely. Looking at this list: magnesium glycinate...
  39. karush

    MHB  Half-Life of Silicon 32 - Kilani High School

    $\tiny{6.1.01}$ this was a homework problem from Kilani High School The half life of silicon 32 is $710$ years. If $10g$ are present now how much will be present in $600$ yrs? find out $k$ using \$\begin{array}{rlll} &A=A_0 e^{kt} & &(1)\\ \textsf{make }A=5 &5=10e^{k \cdot 710} & &(2)\\...
  40. A

    Do scientists have a social life?

    As an aspiring physicist , it worries me to see most of the physicists and mathematicians leading a rather reclusive lifestyle.(which they tend to enjoy and I have no problem with that). I'm very social by nature; I enjoy going to parties, playing sports, going for a vacation and sometimes...
  41. DDTG Global

    Why is life so much more resilient than machines?

    This might sound like a stupid question... Was installing something in my computer last night, gpu was stuck so I pulled with too much force, it just suffered a small chip on the PCB and is now dead. Made me think, humans/animals can lose limbs, organs, even half their brains, and still live...
  42. A

    Black Holes & Life: Myth or Reality?

    Hello everyone, im new in the forum and this is actually my first post. I am not an expert of astrophysics but for sure a very curious person that hope to can get more knowledge about astronomy and physics in the next future. Its been kinda long time I am searching an answer to some questions...
  43. L

    Engineering Where are fixed beams used in real life?

    where are fixed beams used in real life? having real trouble googling them ad finding examples apart from buildings.
  44. S

    I Exploring Life & Technology In A Red Giant Sun's Sphere

    I'm not sure this a strictly Astronomy question; perhaps it should go in Aerospace Engineering. I have always thought that Dyson's work was more of an Astronomy topic, although admittedly, from the POV of observing some other system's sphere. In any case, I was thinking about future...
  45. TimeSkip

    Would you cryogenically freeze yourself?

    There are companies that specialize in cryogenically freezing a person as to treat ailments in the future that aren't yet treatable today. I know there are some preppers here; but, no neologism for cryogenic freezing really exists, maybe cryogenics? Would you ever cryogenically freeze...
  46. B

    Life vs Entropy: Investigating an Unexpected Paradox

    I understand entropy as a movement from order to less order and that the universe's entropy is increasing. So I was wondering, life takes molecules and organizes them into organisms, so isn't life a reversal of entropy?
  47. ShayanJ

    A Life supported by radiation from the accretion disk of a black hole

    For a planet to be able to support life, it needs to have a source of energy. In our case this energy comes from the sun. But in this paper, the author argues that a rogue planet (a planet that has been ejected from its stellar system and no longer orbits any star and is wandering in...
  48. Jarvis323

    Is the world ready to know about extraterrestrial life?

    Within about a month, Perseverance and Tianwen-1 will reach Mars. There is a lot of excitement about these missions, and anticipation of a possible mid-2021 discovery of extraterrestrial life. NASA's chief scientist, Jim Green, thinks we are close, and is worried that people aren't ready for...