Technical Comparision Beetween versions of USB family in transfer modes

TECHNICAL COMPARISION
	USB 2.0	USB 3.0	USB 3.1
	Control transfer	Control transfer	Control transfer
Control Transfer	Control transfers allow access to different parts of a device. Control transfers are intended to support configuration/command/status type communication flows between client software and its function. A control transfer is composed of a Setup bus transaction moving request information from host to function, zero or more Data transactions sending data in the direction indicated by the Setup transaction, and a Status transaction returning status information from function to host. The Status transaction returns “success” when the endpoint has successfully completed processing the requested operation.	The purpose and characteristics of Control Transfers are identical to those defined in the Universal Serial Bus Specification, Revision 2.0.	The purpose and characteristics of Control Transfers are identical to those defined in the Universal Serial Bus Specification, Revision 2.0.
Setup Stage	SETUP transactions are similar in format to an OUT but use a SETUP rather than an OUT PID.A SETUP always uses a DATA0 PID for the data field of the SETUP transaction. The function receiving a SETUP must accept the SETUP data and respond with ACK; if the data is corrupted, discard the data and return no handshake.	During the Setup stage, a SETUP transaction is used to transmit information to a control endpoint of the device. SETUP transactions are similar in format to a Bulk OUT transaction but have the Setup field set to one in the DPH along with the Data Length field set to eight. In addition, the Setup packet always uses a Data sequence number of zero. A device receiving a Setup packet shall respond as defined in Section 8.11.4(USB 3.0). The Direction field shall be set to zero in TPs or DPs exchanged between the host and any control endpoint on the device regardless of the stage or direction of the control transfer. Note that if the endpoint successfully received the SETUP packet, it may return an ACK TP with the NumP field set to zero if it wants to flow control the control transfer. A device shall send an ERDY when it is ready to resume the control transfer (either the Data or Status stage). Note that an endpoint may return an ACK TP with the NumP field set to zero in response to a SETUP packet if it wants to flow control the control transfer. A device must send an ERDY to start the Data or Status stage. Note that the host may resume transactions to any endpoint – even if the endpoint had not returned an ERDY TP after returning a flow control response.	No change
Data Stage	The Data stage, if present, of a control transfer consists of one or more IN or OUT transactions and follows the same protocol rules as bulk transfers. All the transactions in the Data stage must be in the same direction (i.e., all INs or all OUTs). The amount of data to be sent during the data stage and its direction are specified during the Setup stage. If the amount of data exceeds the prenegotiated data packet size, the data is sent in multiple transactions (INs or OUTs) that carry the maximum packet size. Any remaining data is sent as a residual in the last transaction.	The Data stage, if present, of a control transfer consists of one or more IN or OUT transactions and follows the same protocol rules as bulk transfers except that the Direction field shall always be set to zero. The Data stage always starts with the sequence number set to zero. All the transactions in the Data stage shall be in the same direction (i.e., all INs or all OUTs). The maximum amount of data to be sent during the data stage and its direction are specified during the Setup stage. If the amount of data exceeds the data packet size, the data is sent in multiple data packets that carry the maximum packet size. Any remaining data is sent as a residual in the last data packet. Note that all control endpoints only support a burst of one and hence the host can only send or receive one packet at a time to or from a control endpoint.	No change
Status Stage	The Status stage of a control transfer is the last transaction in the sequence. The status stage transactions follow the same protocol sequence as bulk transactions. Status stage for devices operating at high-speed also includes the PING protocol. A Status stage is delineated by a change in direction of data flow from the previous stage and always uses a DATA1 PID. If, for example, the Data stage consists of OUTs, the status is a single IN transaction. If the control sequence has no Data stage, then it consists of a Setup stage followed by a Status stage consisting of an IN transaction.	The Status stage of a control transfer is the last transaction in the sequence. The status stage transaction is identified by a TP with the SubType set to STATUS. In response to a STATUS TP with zero in the Deferred bit, a device shall send an NRDY, STALL, or ACK TP. If a device sends an NRDY TP, the host shall wait for it to send an ERDY TP for that control endpoint before sending another STATUS TP to the device. However the host may resume transactions to any endpoint – even if the endpoint had not returned an ERDY TP after returning a flow control response. If the Deferred bit is set in the STATUS TP, then the device shall send an ERDY TP to indicate to the host that is ready to complete the status stage of the control transfer.	No change
ACK	Function completes	Request completes:ACK TP	ACK TP
NAK/NRDY	Function is busy:NAK	Device is busy :NRDY TP	NRDY TP
STALL	Function has Error	Request has an error : STALL TP	STALL TP
Control Transfer packet size constraints	* An endpoint for control transfers specifies the maximum data payload size that the endpoint can accept from or transmit to the bus. The allowable maximum control transfer data payload sizes for full-speed devices is 8, 16, 32, or 64 bytes; for high-speed devices, it is 64 bytes and for low-speed devices, it is 8 bytes. This maximum applies to the data payloads of the Data packets following a Setup; i.e., the size specified is for the data field of the packet as defined in Chapter 8(USB spec 2.0), not including other information that is required by the protocol. A Setup packet is always eight bytes. A control pipe (including the Default Control Pipe) always uses its wMaxPacketSize value for data payloads. * All Host Controllers are required to have support for 8-, 16-, 32-, and 64-byte maximum data payload sizes for full-speed control endpoints, only 8-byte maximum data payload sizes for low-speed control endpoints, and only 64-byte maximum data payload size for high-speed control endpoints. No Host Controller is required to support larger or smaller maximum data payload sizes.	Control endpoints have a fixed maximum control transfer data payload size of 512 bytes and have a maximum burst size of one. These maximums apply to all data transactions during the data stage of the control transfer.	No change
Control Transfer Direction	Control transfers are supported via bi-directional communication flow over message pipes. As a consequence, when a control pipe is configured, it uses both the input and output endpoint with the specified endpoint number.	The direction of the Data stage is indicated by the bmRequestType field which is present in the first byte of the data payload of the Setup packet.	No change
Variable length data stage	A control pipe may have a variable-length data phase in which the host requests more data than is contained in the specified data structure. When all of the data structure is returned to the host, the function should indicate that the Data stage is ended by returning a packet that is shorter than the MaxPacketSize for the pipe. If the data structure is an exact multiple of wMaxPacketSize for the pipe, the function will return a zero-length packet to indicate the end of the Data stage.	A control pipe may have a variable-length data phase in which the host requests more data than is contained in the specified data structure. When all of the data structure is returned to the host, a device indicates that the Data stage is ended by returning a DP that has a payload less than the maximum packet size for that endpoint. Note that if the amount of data in the data structure that is returned to the host is less than the amount requested by the host and is an exact multiple of maximum packet size then a control endpoint shall send a zero length DP to terminate the data stage.	No change
control Transfer Bus Access constraints	* If the control transfers that are attempted (in an implementation-dependent fashion) consume less than 10% of the frame time for full-/low-speed endpoints or less than 20% of a microframe for high-speed endpoints, the remaining time can be used to support bulk transfers. * A control transfer that has been attempted and needs to be retried can be retried in the current or a future (micro)frame; i.e., it is not required to be retried in the same (micro)frame. * If there are more control transfers than reserved time, but there is additional (micro)frame time that is not being used for isochronous or interrupt transfers, a Host Controller may move additional control transfers as they are available. * If there are too many pending control transfers for the available (micro)frame time, control transfers are selected to be moved over the bus as appropriate. *If there are control transfers pending for multiple endpoints, control transfers for the different endpoints are selected according to a fair access policy that is Host Controller implementation-dependent. * A transaction of a control transfer that is frequently being retried should not be expected to consume an unfair share of the bus time.	*The transactions of a control transfer may be scheduled coincident with transactions for other function endpoints of any defined transfer type. * Retries of control transfers are not given priority over other best effort transactions. *If there are control and bulk transfers pending for multiple endpoints, control transfers for different endpoints are selected for service according to a fair access policy that is host controller implementation-dependent. *SuperSpeed Data Flow Model When a control endpoint delivers a flow control event the host will remove the endpoint from the actively scheduled endpoints. The host will resume the transfer to the endpoint upon receipt of a ready notification from the device.	No change
Control Transfer Data Sequence	The USB provides robust error detection and recovery/retransmission for errors that occur during control transfers. Transmitters and receivers can remain synchronized with regard to where they are in a control transfer and recover with minimum effort. Retransmission of Data and Status packets can be detected by a receiver via data retry indicators in the packet. A transmitter can reliably determine that its corresponding receiver has successfully accepted a transmitted packet by information returned in a handshake to the packet. The protocol allows for distinguishing a retransmitted packet from its original packet except for a control Setup packet. Setup packets may be retransmitted due to a transmission error; however, Setup packets cannot indicate that a packet is an original or a retried transmission.	No change	No change
	Interrupt Transaction	Interrupt Transaction	Interrupt Transaction
Interrupt Transaction	* Guaranteed maximum service period for the pipe * Retry of transfer attempts at the next period, in the case of occasional delivery failure due to error on the bus	* Guaranteed maximum service interval * Guaranteed retry of transfer attempts in the next service interval	No change
Interrupt Transaction data format	The USB imposes no data content structure on communication flows for interrupt pipes.	The USB imposes no data content structure on communication flows for interrupt pipes.	No change
Interrupt Transaction direction	An interrupt pipe is a stream pipe and is therefore always uni-directional. An endpoint description identifies whether a given interrupt pipe’s communication flow is into or out of the host.	An interrupt pipe is a stream pipe and, therefore, is always unidirectional	No change
interrupt Transaction packet size constraints	An endpoint for an interrupt pipe specifies the maximum size data payload that it will transmit or receive. The maximum allowable interrupt data payload size is 64 bytes or less for full-speed. High-speed endpoints are allowed maximum data payload sizes up to 1024 bytes. A high speed, high bandwidth endpoint specifies whether it requires two or three transactions per microframe. Low-speed devices are limited to eight bytes or less maximum data payload size. This maximum applies to the data payloads of the data packets; i.e., the size specified is for the data field of the packet as defined in Chapter 8, not including other protocol-required information. The USB does not require that data packets be exactly the maximum size; i.e., if a data packet is less than the maximum, it does not need to be padded to the maximum size. All Host Controllers are required to support maximum data payload sizes from 0 to 64 bytes for full-speed interrupt endpoints, from 0 to 8 bytes for low-speed interrupt endpoints, and from 0 to 1024 bytes for high- speed interrupt endpoints. See Section 5.9(usb 2.0) for more information about the details of multiple transactions per microframe for high bandwidth high-speed endpoints. No Host Controller is required to support larger maximum data payload sizes.	An endpoint for interrupt transfers specifies the maximum data packet payload size that it can accept from or transmit on the SuperSpeed bus. The only allowable maximum data payload size for interrupt endpoints is 1024 bytes for interrupt endpoints that support a burst size greater than one and can be any size from 1 to 1024 for an interrupt endpoint with a burst size equal to one. The maximum allowable burst size for interrupt endpoints is three. All SuperSpeed interrupt endpoints shall support sequence values in the range [0-31].	No change
Interrupt Transaction Bus Access constraints	Interrupt transfers can be used by low-speed, full-speed, and high-speed devices. High-speed endpoints can be allocated at most 80% of a microframe for periodic transfers. The USB requires that no more than 90% of any frame be allocated for periodic (isochronous and interrupt) full-/low-speed transfers. The bus frequency and (micro)frame timing limit the maximum number of successful interrupt transactions within a (micro)frame for any USB system to less than 108 full-speed one-byte data payloads, or less than 10 low-speed one-byte data payloads, or to less than 134 high-speed one-byte data payloads. A Host Controller, for various implementation reasons, may not be able to provide the above maximum number of interrupt transactions per (micro)frame.	Periodic endpoints may be allocated up to 90% of the total available bandwidth on SuperSpeed. An endpoint for an interrupt pipe specifies its desired service interval bound via its endpoint descriptor. An interrupt endpoint can specify a desired period 2 (bInterval-1) x 125 μs, where bInterval is in the range 1 up to (and including) 16. The USB System Software will use this information during configuration to determine a period that can be sustained. The period provided by the system may be shorter than that desired by the device up to the shortest period defined by the SuperSpeed (125 μs which is also referred to as a bus interval). Note that errors on the bus can prevent an interrupt transaction from being successfully delivered over the bus and consequently exceed the desired period.	No change
Interrupt Transaction data sequence	Interrupt transactions may use either alternating data toggle bits, such that the bits are toggled only upon successful transfer completion or a continuously toggling of data toggle bits. The host in any case must assume that the device is obeying full handshake/retry rules as defined in Chapter 8(usb 2.0). A device may choose to always toggle DATA0/DATA1 PIDs so that it can ignore handshakes from the host. However, in this case, the client software can miss some data packets when an error occurs, because the Host Controller interprets the next packet as a retry of a missed packet.	No change	No change
ACK	Host handshake	Host handshake	No change
NAK/NRDY	function handshake:NAK	Host handshake	No change
STALL	function handshake	Device Error	No change
	Isochronous Transaction	Isochronous Transaction	Isochronous Transaction
Isochronous Transaction	* Guaranteed access to USB bandwidth with bounded latency * Guaranteed constant data rate through the pipe as long as data is provided to the pipe * In the case of a delivery failure due to error, no retrying of the attempt to deliver the data	* Guaranteed bandwidth for transaction attempts on the SuperSpeed bus with bounded latency * Guaranteed data rate through the pipe as long as data is provided to the pipe * No retry	No change
Isochronous Transaction data format	The USB imposes no data content structure on communication flows for isochronous pipes.	The USB imposes no data content structure on communication flows for isochronous pipes.	No change
Isochronous Transaction direction	An isochronous pipe is a stream pipe and is, therefore, always uni-directional. An endpoint description identifies whether a given isochronous pipe’s communication flow is into or out of the host. If a device requires bi-directional isochronous communication flow, two isochronous pipes must be used, one in eachdirection.	No change	No change
Isochronous Transaction packet size constraints	The USB limits the maximum data payload size to 1,023 bytes for each full-speed isochronous endpoint. High-speed endpoints are allowed up to 1024-byte data payloads. A high speed, high bandwidth endpoint specifies whether it requires two or three transactions per microframe	An endpoint for isochronous transfers specifies the maximum data packet payload size that the endpoint can accept from or transmit on SuperSpeed. The only allowable maximum data payload size for isochronous endpoints is 1024 bytes for isochronous endpoints that support a burst size greater than one and can be any size from 0 to 1024 for an isochronous endpoint with a burst size equal to one. The maximum allowable burst size for isochronous endpoints is 16. However an isochronous endpoint can request up to three burst transactions in the same service interval.	No change
Isochronous Transaction Bus Access constraints	The USB requires that no more than 90% of any frame be allocated for periodic (isochronous and interrupt) transfers for full-speed endpoints. High-speed endpoints can allocate at most 80% of a microframe for periodic transfers. The bus frequency and (micro)frame timing limit the maximum number of successful isochronous transactions within a (micro)frame for any USB system to less than 151 full-speed one-byte data payloads and less than 193 high-speed one-byte data payloads. A Host Controller, for various implementation reasons, may not be able to provide the theoretical maximum number of isochronous transactions per (micro)frame.	Periodic endpoints can be allocated up to 90% of the total available bandwidth on SuperSpeed. An endpoint for an isochronous pipe specifies its desired service interval bound via its endpoint descriptor. An isochronous endpoint can specify a desired period 2 (bInterval-1) x 125 μs, where bInterval is in the range 1 to 16. The system software will use this information during configuration to determine whether the endpoint can be added to the host schedule. Note that errors on the bus can prevent an isochronous transaction from being successfully delivered over the bus.	No change
Isochronous Transaction data sequence	Isochronous transfers do not support data retransmission in response to errors on the bus. A receiver can determine that a transmission error occurred. The low-level USB protocol does not allow handshakes to be returned to the transmitter of an isochronous pipe. Normally, handshakes would be returned to tell the transmitter whether a packet was successfully received or not. An endpoint for isochronous transfers never halts because there is no handshake to report a halt condition. Errors are reported as status associated with the IRP for an isochronous transfer, but the isochronous pipe is not halted in an error case. If an error is detected, the host continues to process the data associated with the next (micro)frame of the transfer. Only limited error detection is possible because the protocol for isochronous transactions does not allow per-transaction handshakes.	Isochronous endpoints always transmit data packets starting with sequence number zero in each service interval. Each successive data packet transmitted in the same service interval is sent with the next higher sequence number. The sequence number shall roll over from thirty one to zero when transmitting the thirty second packet. Isochronous endpoints do not support retries and cannot respond with flow control responses.The first data packet sent in any service interval always uses sequence number zero. The host shall be able to accept and send up to 48 data packets (DP) per service interval. The first DP in each service interval shall start with the sequence number set to 0.	Isochronous endpoints always transmit data packets starting with sequence number zero in each service interval. Each successive data packet transmitted in the same service interval is sent with the next higher sequence number. The sequence number shall roll over from thirty one to zero when transmitting the thirty second packet. Isochronous endpoints do not support retries and cannot respond with flow control responses. * The host shall be able to accept and send up to 48 DPs per service interval for devices operating at Gen 1 speed and up to 96 DPs for devices operating at Gen 2 speed.
	Bulk Transaction	Bulk Transaction	Bulk Transaction
Bulk Transaction	* Access to the USB on a bandwidth-available basis * Retry of transfers, in the case of occasional delivery failure due to errors on the bus * Guaranteed delivery of data but no guarantee of bandwidth or latency	* Access to the SuperSpeed bus on a bandwidth available basis * Guaranteed delivery of data, but no guarantee of bandwidth or latency SuperSpeed retains the following characteristics of bulk pipes: * No data content structure is imposed on the communication flow for bulk pipes. * A bulk pipe is a stream pipe and, therefore, always has communication flow either into or out of the host for any pipe instance. If an application requires a bi-directional bulk communication flow, two bulk pipes must be used (one IN and one OUT).	* Access to the Enhanced SuperSpeed bus on a bandwidth available basis * Guaranteed delivery of data, but no guarantee of bandwidth or latency The Enhanced SuperSpeed bus retains the following characteristics of bulk pipes: * No data content structure is imposed on the communication flow for bulk pipes. * A bulk pipe is a stream pipe and, therefore, always has communication flow either into or out of the host for any pipe instance. If an application requires a bi-directional bulk communication flow, two bulk pipes must be used (one IN and one OUT).
Bulk Transaction data format	The USB imposes no data content structure on communication flows for bulk pipes.	No change	No change
Bulk Transaction direction	A bulk pipe is a stream pipe and, therefore, always has communication flowing either into or out of the host for a given pipe. If a device requires bi-directional bulk communication flow, two bulk pipes must be used, one in each direction.	No change	No change
Bulk Transaction packet size constraints	An endpoint for bulk transfers specifies the maximum data payload size that the endpoint can accept from or transmit to the bus. The USB defines the allowable maximum bulk data payload sizes to be only 8, 16, 32, or 64 bytes for full-speed endpoints and 512 bytes for high-speed endpoints. A low-speed device must not have bulk endpoints. This maximum applies to the data payloads of the data packets; i.e., the size specified is for the data field of the packet as defined in Chapter 8(usb 2.0), not including other protocol-required information.	An endpoint for bulk transfers shall set the maximum data packet payload size in its endpoint descriptor to 1024 bytes. It also specifies the burst size that the endpoint can accept from or transmit on the SuperSpeed bus. The allowable burst size for a bulk endpoint shall be in the range of 1 to 16. All SuperSpeed bulk endpoints shall support sequence values in the range [0-31].	No change
Bulk Transaction Bus Access constraints	Only full-speed and high-speed devices can use bulk transfers. The bus frequency and (micro)frame timing limit the maximum number of successful bulk transactions within a (micro)frame for any USB system to less than 72 full-speed eight-byte data payloads or less than 14 high-speed 512-byte data payloads.
Bulk Transaction data sequence	Bulk transactions use data toggle bits that are toggled only upon successful transaction completion to preserve synchronization between transmitter and receiver when transactions are retried due to errors. Bulk transactions are initialized to DATA0 when the endpoint is configured by an appropriate control transfer. The host will also start the first bulk transaction with DATA0. If a halt condition is detected on a bulk pipe due to transmission errors or a STALL handshake being returned from the endpoint, all pending IRPs are retired. Removal of the halt condition is achieved via software intervention through a separate control pipe. This recovery will reset the data toggle bit to DATA0 for the endpoint on both the host and the device. Bulk transactions are retried due to errors detected on the bus that affect a given transaction.	No change	No change
ACK	ACK indicates that the data packet was received without errors and informs the host that it may send the next packet in the sequence.	ACK TP : Host handshake	ACK TP : Host Handshake
NAK/NRDY	NAK indicates that the data was received without error but that the host should resend the data because the function was in a temporary condition preventing it from accepting the data (e.g., buffer full).	No	No
STALL	If the endpoint was halted, STALL is returned to indicate that the host should not retry the transmission because there is an error condition on the function.	No	No

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Cosmic illusion revealed: Gravitational lens magnifies supernova

A team of researchers has announced the discovery of a galaxy that magnified a background type Ia supernova thirtyfold through gravitational lensing.

  Published: Friday, April 25, 2014

Schematic illustration of the magnification by a galaxy. A massive object between us and the supernova bends light rays much as a glass lens can focus light. As more light rays are directed toward the observer than would be without the lens, the supernova appears magnified.

Kavli IPMU

A team of researchers led by Robert Quimby at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan has announced the discovery of a galaxy that magnified a background type Ia supernova thirtyfold through gravitational lensing. This is the first example of strong gravitational lensing of a supernova and confirms the team’s previous explanation for the unusual properties of this supernova.

The team has further shown how such discoveries of supernovae of type Ia (SNIa) can be made far more common than previously thought possible. SNIa seen through gravitational lenses can be used to make a direct measurement of the universe’s expansion rate — the Hubble parameter — so this discovery may have a significant impact on how cosmic expansion is studied in the future.

SNIa are tremendously useful to understand the mysterious components of the universe such as dark energy and dark matter. SNIa have strikingly similar peak luminosities, regardless of where they happen in the universe. This property allows astronomers to use SNIa as standard candles to measure cosmological distance independent of the universe’s expansion. Distance measurement with SNIa was key to the discovery of the accelerating expansion of the universe.

In 2010, scientists found a supernova named PS1-10afx that demonstrated the same color and light curve — the change in brightness over time — as a type Ia supernova, but its peak brightness was 30 times greater than expected. This discovery was made using the Panoramic Survey Telescope & Rapid Response System 1 (Pan-STARRS1), a telescope located in Hawaii that can image the entire visible sky several times each month. This anomaly led some to conclude that it was a completely new type of superluminous supernova. “PS1-10afx looked a lot like a type Ia supernova, “ said Quimby, “but it was just too bright.”

The physics of SNIa have been studied in detail over the past three decades, and there is no known way to produce a SNIa with normal colors and a normal light curve but a substantially higher luminosity.

“Generally, the rare supernovae that have been found to shine brighter than type Ia usually have higher temperatures (bluer colors) and larger physical sizes, and thus slower light curves,” Quimby said. “New physics would thus be required to explain PS1-10afx as an intrinsically luminous supernova.”

“We found a second explanation, and it required only well-demonstrated physics — gravitational lensing,” said Marcus Werner from the Kavli IPMU. “If there was a massive galaxy in front of PS1-10afx, it could warp space-time to form magnified images of the supernova.”

“Although the available observations were consistent with the hypothesis of our team, we needed to answer the question: Where was the lens galaxy?” said Anupreeta More from the Kavli IPMU, “The existing data clearly showed the presence of the supernova’s host galaxy, but there was no evidence for the necessary foreground galaxy. We then tried to find the evidence.”

In September 2013, Quimby’s team set out to find the hidden lens. Using the Low-Resolution Imaging Spectrograph on the 10-meter Keck-I Telescope located in Hawaii, they spent seven hours collecting light at the location of PS1-10afx, which had by then faded away itself.

“After carefully extracting the signal from the data, we had confirmation,” More said. “Buried in the glare of the relatively bright host galaxy, we found a second foreground galaxy. This second galaxy was faint enough to have previously gone unnoticed. But our analysis showed that it was still the right size to explain the gravitational lensing of PS1-10afx.”

“We had existing predictions of what a gravitationally lensed type Ia supernova would look like,” said Masamune Oguri from the Department of Physics at the University of Tokyo. “But the small size of this lens galaxy and the large magnification it produced was not exactly what we were expecting for the first discovery. However, this system may very well prove typical of discoveries to come. Because more distant supernovae are more likely to be gravitationally lensed, lensed supernovae are typically highly magnified and located in the distant universe.”

A consequence of this is that most of the gravitationally lensed SNIa that will be found with future surveys using instruments such as the coming Large Synoptic Survey Telescope can be identified by their colors — the higher redshift, gravitationally lensed supernovae being redder than the more nearby unlensed objects. “Our new approach allows us to find unresolved strong lensing events produced by such low-mass galaxies,” said Oguri. “Thus, the expected number of gravitationally lensed type Ia supernovae to be found in future surveys increases by an order of magnitude.”

“In the future, when a target is identified as a possible lensed type Ia supernova,” said Quimby, “high-resolution follow-up observations can be taken to resolve the individual image components.” Each image comes from the same source but travels a different path length on its way to the observer, so there is an arrival time difference between these multiple supernova images. If this “time delay” can be measured, a direct test of cosmic expansion is possible, faster expansion leads to shorter time delays. By timing the delays precisely and comparing these to the delay expected from the geometry of the lens, the expansion history of the universe can be directly inferred. “The discovery and selection method we have crafted may thus soon improve our understanding of our expanding universe,” Quimby said.

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mY liFe mY waY :Stephen Hawking

Stephen Hawking: God was not needed to create the Universe

The Big Bang was the result of the inevitable laws of physics and did not need God to spark the creation of the Universe, Stephen Hawking has concluded

The scientist has claimed that no divine force was needed to explain why the Universe was formed.

In his latest book, The Grand Design, an extract of which is published in Eureka magazine in The Times, Hawking said: “Because there is a law such as gravity, the Universe can and will create itself from nothing. Spontaneous creation is the reason there is something rather than nothing, why the Universe exists, why we exist.”

He added: “It is not necessary to invoke God to light the blue touch paper and set the Universe going.”

In A Brief History of Time, Prof Hawking's most famous work, he did not dismiss the possibility that God had a hand in the creation of the world.

He wrote in the 1988 book: "If we discover a complete theory, it would be the ultimate triumph of human reason — for then we should know the mind of God.”

Has Stephen Hawking ended the God debate?

Stephen Hawking has declared that his latest work shows there was no creator of the universe. But we shouldn't imagine that will settle the God vs science debate, says Graham Farmelo.

Stephen Hawking: God was not needed to create the Universe

A useful characteristic of a scientific theory is that it must be possible, at least in principle, for experimenters to prove it wrong. Newton and Darwin, two of the greatest theoreticians, both set out ideas in this way, putting their heads on Nature's chopping block. In Newton's case, at least, his ideas have been superseded after proving inadequate in some circumstances. Unlike many religions, science has no final authority; the Royal Society, the UK academy of sciences, expresses this neatly in its motto "Take nobody's word for it".

No religion has ever been set out in terms of scientific statements. This is why scientists are able to mock the claims of religions but have never been able to deal a knock-out blow: in the end, a religious believer can always fall back on a faith that does not depend on verification.

The most famous atheist scientist of our times is the fearless Richard Dawkins, whose God Delusion set out to discredit religion once and for all. For him, it was Darwin's theory of evolution that dealt the fatal blow to religious belief. Powerful and eloquent though it was, religion continues to flourish, and scientists (albeit a minority) continue to go to church, just as Galileo, Newton, Faraday and others have done in the past. I suspect that none of them would have abandoned their respective faiths after reading Dawkins (admittedly, not a scientific statement). Religions will survive so long as they steer clear of making statements that can be shown to be factually wrong.

The kind of science done by Stephen Hawking, one of the leading theoretical physicists of modern times, has an almost religious ring to it. He and his colleagues are trying to find the patterns in the basic fabric of reality – the mathematical laws that govern the workings of nature at its finest level. There is plenty of evidence that these laws hold good all the way back to the beginning of time, which is how scientists have put together an extremely detailed and well-tested theory of the Big Bang, the first few minutes of the universe. The Large Hadron Collider will soon be reproducing, at will, the conditions in the universe within a billionth of a second of the beginning of time.

This has led writers to invest these experiments with a theological significance. The distinguished experimenter Leon Lederman labelled the Higgs particle, being sought at the Collider, as the God Particle, with no good reason except as a hook to promote his book, which he named after it. Yet these experiments will tell us nothing about God. They will simply steer us towards an improved theoretical understanding of our material universe, ultimately in terms of principles set out in mathematics.

Yet this is where religion can sneak back into the picture. Einstein, to the frustration of many of his colleagues, was fond of referring to God when he was talking about the laws expressing the fundamental harmonies of the universe. As Dawkins rightly stresses, it is quite clear that Einstein did not think of God as a white-bearded benefactor capable of interfering with the functioning of the universe. Rather, Einstein followed closely the views of the philosopher Spinoza, for whom the concept of God is an expression of the underlying unity of the universe, something so wondrous that it can command a spiritual awe.

Einstein's views were largely shared by his acquaintance Paul Dirac, the greatest English theoretician since Newton. Dirac, like Newton and Hawking, held the Lucasian Chair of Mathematics at Cambridge University. For Dirac, the greatest mystery of the universe was that its most fundamental laws can be expressed in terms of beautiful mathematical equations. Towards the end of his life, in the 1970s and early 1980s, Dirac often said that mathematical beauty "is almost a religion to me".

As a young man, he was an outspoken atheist, drawing his colleague Wolfgang Pauli to comment, "There is no God and Dirac is his prophet." Decades later, in 1963, Dirac was happy to use theological imagery: "God is a mathematician of a very high order." He was speaking metaphorically, but we know what he meant. Yet I think it is misleading, especially when talking about science to non-specialists, to play fast and loose with the idea of God.

Hawking's view appears to be that the belief in a God-created universe can be supplanted by a belief in M-theory, a good candidate for a fundamental theory of nature at its finest level. Experts assure us of the potential of this theory and I for one am quite prepared to believe them.

One problem with the theory is that it looks as though it will be extremely difficult to test, unless physicists can build a particle accelerator the size of a galaxy. Even if the experimenters find a way round this and M-theory passes all their tests, the reasons for the mathematical order at the heart of the universe's order would remain an unsolvable mystery.

Even religious scientists – and there are still a few – never use the God concept in their scientific work. Perhaps it is time for a moratorium on the use of the concept in popularisations, too? This would avoid mixing up scientific and non-scientific statements and put an end to the consequent confusions. I think it wise for scientists and religious believers to keep out of each other's territory – no good has come out of their engagement and I suspect it never will.

But this is naive. The science-religion relationship, in so far as there is one, continues to be a crowd-pleaser. It seems to be a fundamental law of PR that the God-science debate is a sure-fire source of publicity. Always welcome when one has a book to sell.

Graham Farmelo's biography of theoretical physicist Paul Dirac, 'The Strangest Man', won the Costa Biography Prize and the Los Angeles Times Book Prize

mY liFe mY waY: univers news

Hubble Studies Dark Matter Filament in 3-D

by sandeep janjirala on OCTOBER 16, 2012

Hubble’s view of massive galaxy cluster MACS J0717.5+3745. The large field of view is a combination of 18 separate Hubble images. Credit:
NASA, ESA, Harald Ebeling (University of Hawaii at Manoa) & Jean-Paul Kneib (LAM)

Earlier this year, astronomers using the Hubble Space Telescope were able to identify a slim filament of dark matter that appeared to be binding a pair of distant galaxies together. Now, another filament has been found, and scientists a have been able to produce a 3-D view of the filament, the first time ever that the difficult-to-detect dark matter has been able to be measured in such detail. Their results suggest the filament has a high mass and, the researchers say, that if these measurements are representative of the rest of the Universe, then these structures may contain more than half of all the mass in the Universe.

Dark matter is thought to have been part of the Universe from the very beginning, a leftover from the Big Bang that created the backbone for the large-scale structure of the Universe.

“Filaments of the cosmic web are hugely extended and very diffuse, which makes them extremely difficult to detect, let alone study in 3D,” said Mathilde Jauzac, from Laboratoire d’Astrophysique de Marseille in France and University of KwaZulu-Natal, in South Africa, lead author of the study.

The team combined high resolution images of the region around the massive galaxy cluster MACS J0717.5+3745 (or MACS J0717 for short) – one of the most massive galaxy clusters known — and found the filament extends about 60 million light-years out from the cluster.

The team said their observations provide the first direct glimpse of the shape of the scaffolding that gives the Universe its structure. They used Hubble, NAOJ’s Subaru Telescope and the Canada-France-Hawaii Telescope, with spectroscopic data on the galaxies within it from the WM Keck Observatory and the Gemini Observatory. Analyzing these observations together gives a complete view of the shape of the filament as it extends out from the galaxy cluster almost along our line of sight.

The team detailed their “recipe” for studying the vast but diffuse filament. .

First ingredient: A promising target. Theories of cosmic evolution suggest that galaxy clusters form where filaments of the cosmic web meet, with the filaments slowly funnelling matter into the clusters. “From our earlier work on MACS J0717, we knew that this cluster is actively growing, and thus a prime target for a detailed study of the cosmic web,” explains co-author Harald Ebeling (University of Hawaii at Manoa, USA), who led the team that discovered MACS J0717 almost a decade ago.

Second ingredient: Advanced gravitational lensing techniques. Albert Einstein’s famous theory of general relativity says that the path of light is bent when it passes through or near objects with a large mass. Filaments of the cosmic web are largely made up of dark matter [2] which cannot be seen directly, but their mass is enough to bend the light and distort the images of galaxies in the background, in a process called gravitational lensing. The team has developed new tools to convert the image distortions into a mass map.

Third ingredient: High resolution images. Gravitational lensing is a subtle phenomenon, and studying it needs detailed images. Hubble observations let the team study the precise deformation in the shapes of numerous lensed galaxies. This in turn reveals where the hidden dark matter filament is located. “The challenge,” explains co-author Jean-Paul Kneib (LAM, France), “was to find a model of the cluster’s shape which fitted all the lensing features that we observed.”

Finally: Measurements of distances and motions. Hubble’s observations of the cluster give the best two-dimensional map yet of a filament, but to see its shape in 3D required additional observations. Colour images [3], as well as galaxy velocities measured with spectrometers [4], using data from the Subaru, CFHT, WM Keck, and Gemini North telescopes (all on Mauna Kea, Hawaii), allowed the team to locate thousands of galaxies within the filament and to detect the motions of many of them.

A model that combined positional and velocity information for all these galaxies was constructed and this then revealed the 3D shape and orientation of the filamentary structure. As a result, the team was able to measure the true properties of this elusive filamentary structure without the uncertainties and biases that come from projecting the structure onto two dimensions, as is common in such analyses.

The results obtained push the limits of predictions made by theoretical work and numerical simulations of the cosmic web. With a length of at least 60 million light-years, the MACS J0717 filament is extreme even on astronomical scales. And if its mass content as measured by the team can be taken to be representative of filaments near giant clusters, then these diffuse links between the nodes of the cosmic web may contain even more mass (in the form of dark matter) than theorists predicted.

Timeline: 15 Years of Cassini

by NANCY ATKINSON on OCTOBER 16, 2012

The Cassini spacecraft takes an angled view toward Saturn, showing the southern reaches of the planet with the rings on a dramatic diagonal. Credit: NASA/JPL-Caltech/Space Science Institute

The Cassini mission has been a source of awe-inspiring images, surprising science and incredible longevity. Since launching on Oct. 15, 1997, the Cassini spacecraft has logged more than 6.1 billion kilometers (3.8 billion miles)of exploration – enough to circle Earth more than 152,000 times. After flying by Venus twice, Earth, and then Jupiter on its way to Saturn, Cassini pulled into orbit around the ringed planet in 2004 and has been spending its last eight years weaving around Saturn, its glittering rings and intriguing moons.

The spacecraft has sent back some 444 gigabytes of scientific data so far, including more than 300,000 images. More than 2,500 reports have been published in scientific journals based on Cassini data, describing the discovery of the plume of water ice and organic particles spewing from the moon Enceladus; the first views of the hydrocarbon-filled lakes of Saturn’s largest moon Titan; the atmospheric upheaval from a rare, monstrous storm on Saturn and many other curious phenomena.

The folks from the Cassini mission have put together a great infographic that provides a timeline of Cassini’s mission and some of its “greatest hits” — major events and discoveries. See below:

Extreme Solar Systems: Why Aren’t We Finding Other Planetary Systems Like Our Own?

by sandeep janjirala on OCTOBER 16, 2012

Artist concept of a previous multi-planet solar system found by the Kepler spacecraft. Credit: NASA/Tim Pyle

Most planetary systems found by astronomers so far are quite different than our own. Many have giant planets whizzing around in a compact configuration, very close to their star. An extreme case in point is a newly found solar system that was announced on October 15, 2012 which packs five — count ‘em — five planets into a region less than one-twelve the size of Earth’s orbit!

“This is an extreme example of a compact solar system,” said researcher Darin Ragozzine from the University of Florida, speaking at a press conference at the American Astronomical Society’s Division for Planetary Sciences meeting. “If we can understand this one, hopefully we can understand how these types of systems form and why most known planetary systems appear different from our own solar system.”

This new system, currently named KOI-500, was found with data from the Kepler planet-finding spacecraft, and Ragozzine said astronomers have now uncovered a new realm of exo-planetary systems.

“The real exciting thing is that Kepler has found hundreds of stars with multiple transiting planets,” he said. “These are the most information-rich systems, as they can tell you not only about the planets, but also the architecture of how solar systems are put together.”

The fact that almost all solar systems found so far are vastly different than our own has astronomers wondering if we are, in fact, the oddballs. A study from 2010 concluded that only about 10 – 15 percent of stars in the Universe host systems of planets like our own, with terrestrial planets nearer the star and several gas giant planets in the outer part of the solar system.

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Part of the reason our dataset of exoplanets is skewed with planets that are close to the star is because currently, that is all we are capable of detecting.

But the surprising new population of planetary systems discovered in the Kepler data that contain several planets packed in a tiny space around their host stars does give credence to the thinking that our solar system may be somewhat unique.

However, perhaps KOI-500 used to be more like our solar system.

“From the architecture of this planetary system, we infer that these planets did not form at their current locations,” Ragozzine said. “The planets were originally more spread out and have ‘migrated’ into the ultra-compact configuration we see today.”

There are several theories about the formation of the large planets in our outer solar system which involves the planets moving and migrating inward and outward during the formation process. But why didn’t the inner planets, including Earth, move in closer, too?

“We don’t know why this didn’t happen in our solar system,” Ragozzine said, but added that KOI-500 will “become a touchstone for future theories that will attempt to describe how compact planetary systems form. Learning about these systems will inspire a new generation of theories to explain why our solar system turned out so differently.”

A few notes of interest about KOI-500:

The five planets have “years” that are only 1.0, 3.1, 4.6, 7.1, and 9.5 days.

“All five planets zip around their star within a region 150 times smaller in area than the Earth’s orbit, despite containing more material than several Earths (the planets range from 1.3 to 2.6 times the size of the Earth). At this rate, you could easily pack in 10 more planets, and they would still all fit comfortably inside the Earth’s orbit,” Ragozzine noted. KOI-500 is approximately 1,100 light-years away in the constellation Lyra, the harp.

Four of the planets orbiting KOI-500 follow synchronized orbits around their host star in a completely unique way — no other known system contains a similar configuration. Work by Ragozzine and his colleagues suggests that planetary migration helped to synchronize the planets.

“KOI” stands for Kepler Object of Interest, and Ragozzine’s findings on this system have not yet been published, and so the system has yet to officially be considered a confirmed planetary system. “Every time we find something like this we give it a license-plate-like number starting with KOI,” Ragozzine said.

When does a KOI become an official planet? Ragozzine said the process is by confirming and validating the data. “Basically you need to prove statistically or by getting a specific measurement that it is not some other astronomical signal,” he said.