The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time. In imperial units this speed is approximately 186,282 miles per second. According to special relativity, c is the maximum speed at which all energy, matter, and information in the universe can travel. It is the speed at which all massless particles and associated fields (including electromagnetic radiation such as light) travel in vacuum. It is also the speed of gravity (i.e. of gravitational waves) predicted by current theories. Such particles and waves travel at c regardless of the motion of the source or the inertial frame of reference of the observer. In the theory of relativity, c interrelates space and time, and also appears in the famous equation of mass–energy equivalence E = mc2.
The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s slower than c.
If c is generally not constant, then theory of relativity is ONLY theory, which specifically might be applied in vacuum space only! Still we have to assume speed of light remain contant, whether the observed object is moving or is stationary....
To compare someone on Earth (if we say stationary, still Earth is rotating!), and someone moving in aerospace (in the case of twin paradox), still there are A LOT of uncertainties.... not to mention about the speed of light is not constant in both places (Earth and Aerospace) Last edited by mnm77 on 2-4-2013 04:22 PM
Adakah halaju cahaya sama saja dalam semua medium, dalam udara, dalam air, dalam vakum? ...
my answer is yes dalam vaccum...
tapi dalam medium lain, tidak sama sekali...because the energy is conserved disebabkan cahaya ini tiada mass...oleh sebab itu, cahaya retains balik its speed selepas kuar dari medium tersebut...kat sini kita tak leh anggap cahaya sbg partikel tp lebih kpd gelombang cahaya...
dlm erti kata lain, kita boleh view cahaya not just as "particle", tetapi as "electromagnetic wave"...
ini hasil penemuan dr De Broglie yg perkenalkan teori saying that a particle can behave like a wave & a wave can behave like a wave...becoming fundamental theory of quantum mechanics...
kesimpulannya, if pemalar c itu berubah, maka E tidak sama lagi ngan mc2...dan kita tak leh lagi gunakan satu-satunya entiti dpt dilihat dengan mata sbg perbandingan jika kita beranggap c tidak malar...
it is just like we are trying to measure a car moving ngan an acceleration dan cara kita nak measure ngan guna conventional method...
same thing if and only if velocity, c changes with time...yang mana kita kena dapatkan "measurement" by experiment to futher develop theory2 lain selepas itu...
for physicist, we just okay with estimation....slightly changes dari nilai sebenar wont change so much the nature of law...
experiment baru ni pun show tht they obtain a slightly changed c , jadi perkembangan ini tidak cukup utk debunk special relativity theory...unless there is betul2 proven techniques (mencapai piawai with almost perfect estimation) to prove that nilai c berubah 1/2 from that, 1/4 from tht , then kita kena terima perubahan ini...
semuanya akan reformulate balik...
dauswq posted on 2-4-2013 04:18 PM
for physicist, we just okay with estimation....slightly changes dari nilai sebenar wont change so much the nature of law...
experiment baru ni pun show tht they obtain a slightly changed c , jadi perkembangan ini tidak cukup utk debunk special relativity theory...unless there is betul2 proven techniques (mencapai piawai with almost perfect estimation) to prove that nilai c berubah 1/2 from that, 1/4 from tht , then kita kena terima perubahan ini...
semuanya akan reformulate balik...
My original queries was not to debunk theory of relativity, masih berguna teori tu, tapi untuk menyatakan 'c' is constant relative to everything, which is then used to explain time dilation, in my opinion, has not been properly justified.
mnm77 posted on 2-4-2013 04:14 PM
If c is generally not constant, then theory of relativity is ONLY theory, which specifically might b ...
again twin paradox tu just dummy explaination...tak delah guna tuk experimental purpose
earth is not rotating in such a way that it can affect the motion of travelling particles...
dlm konteks ini, rotating earth just jadi penanda aras umur kembar tersebut...
satu putaran, satu hari elapsed dan same gak keadaannya bile seseorang itu di dalam kapal angkasa lepas...die pun anggap perkara yg sama...
saya tak nampak apa relationshipnya ngan motion of travelling object sbb as long as centre of mass is not moving, bumi boleh kita anggap sbg at rest...
lagi satu, compared the rotational speed with c, the ratio is ~10^7....so pada saya, perubahan umur yg ketara disebabkan relativiti dr frame yg sama tidak sgt berbeza jikakalau this rotational speed mainkan peranan...
mnm77 posted on 2-4-2013 04:34 PM
My original queries was not to debunk theory of relativity, masih berguna teori tu, tapi untuk men ...
yup saya faham argument saudara..
pada masa yg sama, sedara pun tambah knowledge , saya pun sama...
bagi saya perbincangan ini benefit us in learning these paradox theories...
berbalik pd soalan,
time dilation mungkin sedara tak accept dlm konteks lif & twin paradox ni sbb ia kurang masuk akal, pd saya pun ya unless teknologi kita dah sampai ke arah situ...
tp ni jugak yg digunakan theorist dan digunakan kita sekarang tuk explain tiny particles's motion...
nuclear development pun berkembang sbb theori ni gak...
dauswq posted on 2-4-2013 04:47 PM
yup saya faham argument saudara..
pada masa yg sama, sedara pun tambah knowledge , saya pun sama...
bagi saya perbincangan ini benefit us in learning these paradox theories...
Haha
berbalik pd soalan,
time dilation mungkin sedara tak accept dlm konteks lif & twin paradox ni sbb ia kurang masuk akal, pd saya pun ya unless teknologi kita dah sampai ke arah situ...
tp ni jugak yg digunakan theorist dan digunakan kita sekarang tuk explain tiny particles's motion...
nuclear development pun berkembang sbb theori ni gak...
Well... bahagian time dilation tu je yang saya agak skeptical, saya masih tidak menolak sepenuhnya teori tu, cuma belum dapat hadam sepenuhnya untuk terima, mungkin kalau ada further expalanation akan lebih faham kot, tapi, so far, macam ada faedahnya dalam melihat kembali relativity theory
Pasal tiny particle's motion, adakah motion tu pun ada directly related to time dilation? Kalau ada kaitannya dengan time dilation, menarik .... kena kaji lebih lah kot untuk dapatkan satisfactory explanation...
Researchers buat research berdasarkan apa yang hukum alam benarkan......setakat ini.
Ok, so now kenapa kita setkan the limit at the speed of light, adalah kerana banyak particles dalam dunia ini yang boleh reach close to the speed of light. Dan hanya photon (partikel cahaya) yang boleh travel at the speed of light.
So, kenapa researchers nak pecahkan pekung had alam ni? Sebab alam ini ada antropi (disorder, chaos) yang in sense means that ada banyak lagi configurations for this world. Sebab chaos ada banyak bentuk. (macam puzzle, kalau tersusun ada satu sahaja gambar, kalau bersepah?). So thats why researchers tengok kat susunan yang macam mana boleh dapat different things. Tapi, in the end, only time will tell.
Memang menarik benda ini, sebab inilah ada falsafah dalam sains. And apa kita akan faham tahun depan macam, Ya Allah, tak sabarnya!
yang paling memeningkan kepala bangkem tentang teori relativiti ialah masa silam, masa sekarang dan masa depan sebenarnya berlaku secara serentak
walupon kita sekarang hidup di dalam tahun 2015, tapi bagi observer yang berada bertahun-tahun cahaya dari bumi, bumi sekarang mungkin berada pada tahun 2100, atau 1900..
paham tak??? tahun 2100 sedang berlaku sekarang, walaupon sekarang kita masih hidup di tahun 2015..
bukan tahun 2100 je.. tahun 2200, 2111, 1999, 1900, 790 sebelum masihi, 1415 hijrah semua tahun tu sedang berlaku sekarang..
walaupon dah diset 300 juta meter sesaat adalah speed limit, tapi ada banyak benda yang perlukan speed yang lebih laju, supaya "program" yang Allah cipta ni boleh berfungsi dengan lancar...
Allah sembunyikan loophole ni ke tahap sub-atomic level, supaya sims dan karekter dalam program ni kelak tidak boleh manipulasi loophole ni
loophole ni digelar "quantum entanglement" di mana dua partikel ni boleh hantar isyarat instantly walaupon pada jarak yang sangat jauh
einstein sendiri kata fenomena ni sebagai "spooky"
Post time 2-4-2013 04:01 PM
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